Searching for Scalar Ultralight Dark Matter with Optical Fibers [CL]

http://arxiv.org/abs/2305.11205


We consider optical fibers as detectors for scalar ultralight dark matter (UDM) and propose using a fiber-based interferometer to search for scalar UDM with particle mass in the range $10^{-17} – 10^{-13}$ eV/$c^2$ $\left(10^{-3}- 10 \text{ Hz}\right)$. Composed of a solid core and a hollow core fiber, the proposed detector would be sensitive to relative oscillations in the fibers’ refractive indices due to scalar UDM-induced modulations in the fine-structure constant $\alpha$. We predict that, implementing detector arrays or cryogenic cooling, the proposed optical fiber-based scalar UDM search has the potential to reach new regions of the parameter space. Such a search would be particularly well-suited to probe for a Solar halo of dark matter with a sensitivity exceeding that of previous DM searches over the particle mass range $7\times 10^{-17} – 2\times 10^{-14}$ eV/$c^2$.

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J. Manley, R. Stump, R. Petery, et. al.
Mon, 22 May 23
43/60

Comments: N/A

Mitigating the Non-Linearities in a Pyramid Wavefront Sensor [IMA]

http://arxiv.org/abs/2305.09805


For natural guide start adaptive optics (AO) systems, pyramid wavefront sensors (PWFSs) can provide significant increase in sensitivity over the traditional Shack-Hartmann, but at the cost of a reduced linear range. When using a linear reconstructor, non-linearities result in wavefront estimation errors, which can have a significant impact on the image quality delivered by the AO system. Here we simulate a wavefront passing through a PWFS under varying observing conditions to explore the possibility of using a non-linear machine learning model to estimate wavefront errors better than a linear reconstruction. We find significant improvement even with light-weight models, underscoring the need for further investigation of this approach.

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F. Archinuk, R. Hafeez, S. Fabbro, et. al.
Thu, 18 May 23
14/67

Comments: N/A

Visible to Ultraviolet Frequency Comb Generation in Lithium Niobate Nanophotonic Waveguides [CL]

http://arxiv.org/abs/2305.08006


The introduction of nonlinear nanophotonic devices to the field of optical frequency comb metrology has enabled new opportunities for low-power and chip-integrated clocks, high-precision frequency synthesis, and broad bandwidth spectroscopy. However, most of these advances remain constrained to the near-infrared region of the spectrum, which has restricted the integration of frequency combs with numerous quantum and atomic systems in the ultraviolet and visible. Here, we overcome this shortcoming with the introduction of multi-segment nanophotonic thin-film lithium niobate (LN) waveguides that combine engineered dispersion and chirped quasi-phase matching for efficient supercontinuum generation via the combination of $\chi^{(2)}$ and $\chi^{(3)}$ nonlinearities. With only 90 pJ of pulse energy at 1550 nm, we achieve gap-free frequency comb coverage spanning 330 to 2400 nm. The conversion efficiency from the near-infrared pump to the UV-Visible region of 350-550 nm is nearly 20%. Harmonic generation via the $\chi^{(2)}$ nonlinearity in the same waveguide directly yields the carrier-envelope offset frequency and a means to verify the comb coherence at wavelengths as short as 350 nm. Our results provide an integrated photonics approach to create visible and UV frequency combs that will impact precision spectroscopy, quantum information processing, and optical clock applications in this important spectral window.

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T. Wu, L. Ledezma, C. Fredrick, et. al.
Tue, 16 May 23
38/83

Comments: N/A

Misalignment and mode mismatch error signals for higher-order Hermite-Gauss modes from two sensing schemes [IMA]

http://arxiv.org/abs/2305.03658


The locking of lasers to optical cavities is ubiquitously required in the field of precision interferometry such as Advanced LIGO to yield optimal sensitivity. Using higher-order Hermite-Gauss (HG) modes for the main interferometer beam has been a topic of recent study, due to their potential for reducing thermal noise of the test masses. It has been shown however that higher-order HG modes are more susceptible to coupling losses into optical cavities: the misalignment and mode mismatch induced power losses scale as $2n+1$ and $n^{2}+n+1$ respectively with $n$ being the mode index. In this paper we calculate analytically for the first time the alignment and mode mismatch sensing signals for arbitrary higher-order HG modes with both the traditional sensing schemes (using Gouy phase telescopes and quadrant photodetectors) and the more recently proposed radio-frequency jitter-based sensing schemes (using only single element photodiodes). We show that the sensing signals and also the signal-to-shot noise ratios for higher-order HG modes are larger than for the fundamental mode. In particular, the alignment and mode mismatch sensing signals in the traditional sensing schemes scale approximately as $\sqrt{n}$ and $n$ respectively, whereas in the jitter-based sensing schemes they scale exactly as $2n+1$ and $n^{2}+n+1$, respectively, which exactly matches the decrease in their respective tolerances. This potentially mitigates the downside of higher-order HG modes for their suffering from excessive misalignment and mode-mismatch induced power losses.

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L. Tao, A. Green and P. Fulda
Mon, 8 May 23
34/63

Comments: 11 pages 6 figures

Beam displacement tolerances on a segmented mirror for higher-order Hermite-Gauss modes [IMA]

http://arxiv.org/abs/2305.03681


Odd-indexed higher-order Hermite-Gauss (HG) modes are compatible with 4-quadrant segmented mirrors due to their intensity nulls along the principal axes, which guarantees minimum beam intensity illuminating the bond lines between the segments thus leading to low power loss. However, a misplaced HG beam can cause extra power loss due to the bright intensity spots probing the bond lines. This paper analytically and numerically studies the beam displacement tolerances on a segmented mirror for the $\mathrm{HG_{3,3}}$ mode. We conclude that for “effective” bond lines with 6 $\mu$m width, and the $\mathrm{HG_{3,3}}$ beam size chosen to guarantee 1 ppm clipping loss when centered, the beam can be rotated by roughly 1 degree or laterally displaced by 4% of its beam size while keeping the total power on the bond lines under 1 ppm. We also demonstrate that the constrained beam displacement parameter region that guarantees a given power loss limit, or the beam displacement tolerance, is inversely proportional to the bond line thickness.

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L. Tao, N. Brown and P. Fulda
Mon, 8 May 23
45/63

Comments: 4 pages, 6 pages

Substrate-transferred GaAs/AlGaAs crystalline coatings for gravitational-wave detectors: A review of the state of the art [CL]

http://arxiv.org/abs/2301.02687


In this Perspective we summarize the status of technological development for large-area and low-noise substrate-transferred GaAs/AlGaAs (AlGaAs) crystalline coatings for interferometric gravitational-wave (GW) detectors. These topics were originally presented in a workshop{\dag} bringing together members of the GW community from the laser interferometer gravitational-wave observatory (LIGO), Virgo, and KAGRA collaborations, along with scientists from the precision optical metrology community, and industry partners with extensive expertise in the manufacturing of said coatings. AlGaAs-based crystalline coatings present the possibility of GW observatories having significantly greater range than current systems employing ion-beam sputtered mirrors. Given the low thermal noise of AlGaAs at room temperature, GW detectors could realize these significant sensitivity gains, while potentially avoiding cryogenic operation. However, the development of large-area AlGaAs coatings presents unique challenges. Herein, we describe recent research and development efforts relevant to crystalline coatings, covering characterization efforts on novel noise processes, as well as optical metrology on large-area (~10 cm diameter) mirrors. We further explore options to expand the maximum coating diameter to 20 cm and beyond, forging a path to produce low-noise AlGaAs mirrors amenable to future GW detector upgrades, while noting the unique requirements and prospective experimental testbeds for these novel materials.

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G. Cole, S. Ballmer, G. Billingsley, et. al.
Tue, 10 Jan 23
36/93

Comments: 13pages, 3 figures

Interferometric imaging using shared quantum entanglement [CL]

http://arxiv.org/abs/2212.07395


Entanglement-based imaging promises significantly increased imaging resolution by extending the spatial separation of collection apertures used in very-long-baseline interferometry for astronomy and geodesy. We report a table-top quantum-entanglement-based interferometric imaging technique that utilizes two entangled field modes serving as a phase reference between two apertures. The spatial distribution of the source is determined by interfering light collected at each aperture with one of the entangled fields and making joint measurements. This approach provides a route to increase angular resolution while maximizing the information gained per received photon.

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M. Brown, M. Allgaier, V. Thiel, et. al.
Thu, 15 Dec 22
53/75

Comments: N/A

A superconducting nanowire photon number resolving four-quadrant detector-based Gigabit deep-space laser communication receiver prototype [CL]

http://arxiv.org/abs/2212.04927


Deep space explorations require transferring huge amounts of data quickly from very distant targets. Laser communication is a promising technology that can offer a data rate of magnitude faster than conventional microwave communication due to the fundamentally narrow divergence of light. This study demonstrated a photon-sensitive receiver prototype with over Gigabit data rate, immunity to strong background photon noise, and simultaneous tracking ability. The advantages are inherited from a joint-optimized superconducting nanowire single-photon detector (SNSPD) array, designed into a four-quadrant structure with each quadrant capable of resolving six photons. Installed in a free-space coupled and low-vibration cryostat, the system detection efficiency reached 72.7%, the detector efficiency was 97.5%, and the total photon counting rate was 1.6 Gcps. Additionally, communication performance was tested for pulse position modulation (PPM) format. A series of signal processing methods were introduced to maximize the performance of the forward error correction (FEC) code. Consequently, the receiver exhibits a faster data rate and better sensitivity by about twofold (1.76 photons/bit at 800 Mbps and 3.40 photons/bit at 1.2 Gbps) compared to previously reported results (3.18 photon/bit at 622 Mbps for the Lunar Laser Communication Demonstration). Furthermore, communications in strong background noise and with simultaneous tracking ability were demonstrated aimed at the challenges of daylight operation and accurate tracking of dim beacon light in deep space scenarios.

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H. Hao, Q. Zhao, Y. Huang, et. al.
Mon, 12 Dec 22
2/52

Comments: N/A

Bound state properties and positron annihilation in the negatively charged Ps$^{-}$ ion. On thermal sources of annihilation $γ$-quanta in our Galaxy [CL]

http://arxiv.org/abs/2212.03723


The total energy and other bound state properties of the ground (bound) $1^{1}S$-state in the Ps$^{-}$ ion are determined to very high accuracy. Our best variational energy for the ground state in this ion equals $E$ = -0.262005070232980107770402018838 $a.u.$ For this three-body ion we have evaluated (to very high accuracy) the rates of two-, three-, four- and five-photon annihilation. We also discuss some problems which currently exist in accurate computations of the rate of one-photon annihilation $\Gamma_{1 \gamma}$. Highly accurate computations of a number of singular and quasi-singular bound state properties in the Ps$^{-}$ ion are also performed and discussed. By investigating the sources of annihilation $\gamma-$quanta in the universe we have arrived to the conclusion about the high-temperature limit in optics. This can be formulated by the following statement: due to the electromagnetic instability of the vacuum, it is impossible to see (directly) any object heated to temperatures above 350 – 400 $keV$. In reality, instead of such an object an observer will see only an intense flow of annihilation $\gamma-$quanta, electrons and positrons. This phenomenon can be called the annihilation shielding of overheated matter and it is of great interest in Galactic astrophysics.

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A. Frolov
Thu, 8 Dec 22
29/63

Comments: N/A

Wide-spectrum optical synthetic aperture imaging via spatial intensity interferometry [CL]

http://arxiv.org/abs/2212.01036


High resolution imaging is achieved using increasingly larger apertures and successively shorter wavelengths. Optical aperture synthesis is an important high-resolution imaging technology used in astronomy. Conventional long baseline amplitude interferometry is susceptible to uncontrollable phase fluctuations, and the technical difficulty increases rapidly as the wavelength decreases. The intensity interferometry inspired by HBT experiment is essentially insensitive to phase fluctuations, but suffers from a narrow spectral bandwidth which results in a lack of detection sensitivity. In this study, we propose optical synthetic aperture imaging based on spatial intensity interferometry. This not only realizes diffraction-limited optical aperture synthesis in a single shot, but also enables imaging with a wide spectral bandwidth. And this method is insensitive to the optical path difference between the sub-apertures. Simulations and experiments present optical aperture synthesis diffraction-limited imaging through spatial intensity interferometry in a 100 $nm$ spectral width of visible light, whose maximum optical path difference between the sub-apertures reach $69.36\lambda$. This technique is expected to provide a solution for optical aperture synthesis over kilometer-long baselines at optical wavelengths.

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C. Chu, Z. Liu, M. Chen, et. al.
Mon, 5 Dec 22
37/63

Comments: N/A

Space-Time Projection Optical Tomography: Search Space and Orbit Determination [CL]

http://arxiv.org/abs/2211.13040


In a companion article, we discussed the radiometric sensitivity and resolution of a new passive optical sensing technique, Space-Time Projection Optical Tomography (SPOT), to detect and track sub-cm and larger space debris for Space Situational Awareness. SPOT is based on the principle that long synthetic exposure can be achieved if the phase-space trajectory of a hypothetical point-source is precisely predictable within a very wide telescope field-of-view, which is the case for orbiting debris. This article discusses the computational search space for debris mining as well as a recursive measure-and-fit algorithm based on a generalized Hough transform for orbit determination.

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H. Bahcivan and D. Brady
Thu, 24 Nov 22
56/71

Comments: N/A

Space-Time Projection Optical Tomography: Search Space and Orbit Determination [CL]

http://arxiv.org/abs/2211.13040


In a companion article, we discussed the radiometric sensitivity and resolution of a new passive optical sensing technique, Space-Time Projection Optical Tomography (SPOT), to detect and track sub-cm and larger space debris for Space Situational Awareness. SPOT is based on the principle that long synthetic exposure can be achieved if the phase-space trajectory of a hypothetical point-source is precisely predictable within a very wide telescope field-of-view, which is the case for orbiting debris. This article discusses the computational search space for debris mining as well as a recursive measure-and-fit algorithm based on a generalized Hough transform for orbit determination.

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H. Bahcivan and D. Brady
Thu, 24 Nov 22
69/71

Comments: N/A

Radiometric sensitivity and resolution of synthetic tracking imaging for orbital debris monitoring [EPA]

http://arxiv.org/abs/2211.09789


We consider sampling and detection strategies for solar illuminated space debris. We argue that the lowest detectable debris cross section may be reduced by 10-100x by analysis of phase-space-pixels rather than single frame data. The phase-space-pixel is a weighted stacking of pixels corresponding to a test debris trajectory within the very wide camera field-of-view (FOV). To isolate debris signals from background, exposure time is set to match the time it takes a debris to transit through the instantaneous field of view. Debris signatures are detected though a generalized Hough transform of the data cube. Radiometric analysis of line integrals shows that that sub-cm objects in Low Earth Orbit can be detected and assigned full orbital parameters by this approach

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H. Bahcivan, D. Brady and G. Hageman
Fri, 18 Nov 22
52/70

Comments: N/A

Advanced LIGO, LISA, and Cosmic Explorer as dark matter transducers [CL]

http://arxiv.org/abs/2210.17487


We present a method to search for scalar field ultralight dark matter directly interacting with gravitational-wave interferometers via a modulation of the fine structure constant and the electron mass. This modulation induces an effective strain in solid materials at a frequency determined by the mass of the dark matter particle. We study the prospects for looking for such an effect in the LIGO detectors by using the solid cavity which is nominally used for pre-stabilizing the laser frequency and we project upper limits. We contextualize them with previous limits from GEO600, possible limits from a similar strain in the LIGO beamsplitter, and with potential limits from upcoming experiments like LISA, Cosmic Explorer and from an upgraded solid cavity. We find that with the sensitivity of Advanced LIGO, competitive upper limits on DM coupling can be placed at the level of $\left\vert d_{m_e}+d_e\right\vert \sim 0.2$ for $m_\text{DM} \sim 10^{-13}\,\mathrm{eV}/\mathrm{c}^2$ with a combination of two searches using the solid cavity and the beamsplitter in LIGO; future experiments could reduce this upper limit to $\sim10^{-3}$.

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E. Hall and N. Aggarwal
Tue, 1 Nov 22
36/100

Comments: 9 pages, 5 figures

Image-Plane Self-Calibration in Interferometry [IMA]

http://arxiv.org/abs/2210.17290


We develop a new process of image plane self-calibration for interferometric imaging data. The process is based on Shape-Orientation-Size (SOS) conservation for the principal triangle in an image generated from the three fringes made from a triad of receiving elements, in situations where interferometric phase errors can be factorized into element-based terms. The basis of the SOS conservation principle is that, for a 3-element array, the only possible image corruption due to an element-based phase screen is a tilt of the aperture plane, leading to a shift in the image plane. Thus, an image made from any 3-element interferometer represents a true image of the source brightness, modulo an unknown translation. Image plane self-calibration entails deriving the unknown translations for each triad image via cross-correlation of the observed triad image with a model image of the source brightness. After correcting for these independent shifts, and summing the aligned triad images, a good image of the source brightness is generated from the full array, recovering source structure at diffraction-limited resolution. The process is iterative, using improved source models based on previous iterations. We demonstrate the technique in the high signal-to-noise context, and include a configuration based on radio astronomical facilities, and simple models of double sources. We show that the process converges for the simple models considered, although convergence is slower than for aperture-plane self-calibration for large-$N$ arrays. As currently implemented, the process is most relevant for arrays with a small number of elements. More generally, the technique provides geometric insight into closure phase and the self-calibration process. The technique is generalizable to non-astronomical interferometric imaging applications across the electromagnetic spectrum.

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C. Carilli, B. Nikolic and N. Thyagarajan
Tue, 1 Nov 22
43/100

Comments: 17 pages 4 figures. To appear in Journal Optical Society America – A

The estimation of far-field wavefront error of tilt-to-length distortion coupling in space-based gravitational wave detection [IMA]

http://arxiv.org/abs/2210.16317


In space-based gravitational wave detection, the estimation of far-field wavefront error of the distorted beam is the precondition for the noise reduction. Zernike polynomials is used to describe the wavefront error of the transmitted distorted beam. The propagation of a laser beam between two telescope apertures is calculated numerically. Far-field wavefront error is estimated with the absolute height of the peak-to-valley phase deviation between distorted Gaussian beam and a reference distortion-free Gaussian beam. The results show the pointing jitter is strongly related to the wavefront error. Furthermore, when jitter decreases 10 times from 100 to 10 nrad, wavefront error reduces for more than an order of magnitude. In the analysis of multi-parameter minimization, the minimum of wavefront error tends to Z[5,3] Zernike in some parameter ranges. Some Zernikes have a strong correlation with wavefront error of the received beam. When the aperture diameter increases at Z[5,3] Zernike, wavefront error is not monotonic and has oscillation. Nevertheless, wavefront error almost remains constant with the arm length increasing from 10$^{-1}$ Mkm to 10$^3$ Mkm. When the arm length decreases for three orders of magnitude from 10$^{-1}$ Mkm to 10$^{-4}$ Mkm, wavefront error has only an order of magnitude increasing. In the range of 10$^{-4}$ Mkm to 10$^3$ Mkm, the lowest limit of the wavefront error is from 0.5 fm to 0.015 fm, at Z[5,3] Zernike and 10 nrad jitter.

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Y. Tao, H. Jin and Y. Wu
Tue, 1 Nov 22
94/100

Comments: 13 pages, 7 figures

Excess noise in highly reflective crystalline mirror coatings [CL]

http://arxiv.org/abs/2210.15671


Thermodynamically induced length fluctuations of high-reflectivity mirror coatings put a fundamental limit on sensitivity and stability of precision optical interferometers like gravitational wave detectors and ultra-stable lasers. The main contribution – Brownian thermal noise – is related to the mechanical loss of the coating material. Owing to their low mechanical losses, Al\textsubscript{0.92}Ga\textsubscript{0.08}As/GaAs crystalline mirror coatings are expected to reduce this limit. At room temperature they have demonstrated lower Brownian thermal noise than with conventional amorphous coatings. %However, no detailed study on the noise constituents from these coatings in optical interferometers has been conducted. We present a detailed study on the spatial and temporal noise properties of such coatings by using them in two independent cryogenic silicon optical Fabry-Perot resonators operated at 4 K, 16 K and 124 K. We confirm the expected low Brownian thermal noise, but also discover two new noise sources that exceed the Brownian noise: birefringent noise that can be canceled via polarization averaging and global excess noise (10 dB above Brownian noise). These new noise contributions are a barrier to improving ultra-stable lasers and the related performance of atomic clocks, and potentially limit the sensitivity of third-generation gravitational wave detectors. Hence, they must be considered carefully in precision interferometry experiments using similar coatings based on semiconductor materials.

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J. Yu, D. Kedar, S. Häfner, et. al.
Mon, 31 Oct 22
3/60

Comments: N/A

Density and infrared band strength of interstellar carbon monoxide (CO) ice analogues [IMA]

http://arxiv.org/abs/2210.15768


The motivation to study experimentally CO ice under mimicked interstellar conditions is supported by the large CO gas abundances and ubiquitous presence of CO in icy grain mantles. Upon irradiation in its pure ice form, this highly stable species presents a limited ion and photon-induced chemistry, and an efficient non-thermal desorption. Using infrared spectroscopy, single laser interference, and quadrupole mass spectrometry during CO ice deposition, the CO ice density was estimated as a function of deposition temperature. Only minor variations in the density were found. The proposed methodology can be used to obtain the density of other ice components at various deposition temperatures provided that this value of the density is known for one of these temperatures, which is typically the temperature corresponding to the crystalline form. The apparent tendency of the CO ice density to decrease at deposition temperatures below 14 K is in line with recently published colorimetric measurements. This work allowed to revisit the value of the infrared band strength needed for calculation of the CO ice column density in infrared observations, $8.7 \times 10^{-18} ~ {\rm cm ~ molecule}^{-1}$ at 20 K deposition temperature.

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C. Díaz, H. Carrascosa, G. Caro, et. al.
Mon, 31 Oct 22
34/60

Comments: 21 pages, 9 figures

Light pollution and the concentration of anthropogenic photons in the terrestrial atmosphere [IMA]

http://arxiv.org/abs/2210.14131


Light pollution can be rigorously described in terms of the volume concentration of anthropogenic photons (light quanta) in the terrestrial atmosphere. This formulation, consistent with the basic physics of the emission, scattering and absorption of light, allows one to express light pollution levels in terms of particle volume concentrations, in a completely analogous way as it is currently done with other classical pollutants, like particulate matter or molecular contaminants. In this work we provide the explicit conversion equations between the photon volume concentration and the traditional light photometry quantities. This equivalent description of the light pollution levels provides some relevant insights that help to identify artificial light at night as a standard pollutant. It also enables a complementary way of expressing artificial light exposures for environmental and public health research and regulatory purposes.

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S. Bará, C. Bao-Varela and F. Falchi
Wed, 26 Oct 22
35/73

Comments: 15 pages, 2 figures. This is an author-formatted version of the accepted manuscript whose version of record has been published in Atmospheric Pollution Research, 2022, 13(9):101541, this https URL

Active focal-plane coronagraphy with liquid-crystal spatial-light modulators: Broadband contrast performance in the visible [IMA]

http://arxiv.org/abs/2210.14000


The technological progress in spatial-light modulators (SLM) technology has made it possible to use those devices as programmable active focal-plane phase coronagraphic masks, opening the door to novel versatile and adaptive high-contrast imaging observation strategies. However, the scalar nature of the SLM-induced phase response is a potential hurdle when applying the approach to wideband light, as is typical in astronomical imaging. For the first time, we present laboratory results with broadband light (up to ~12pc bandwidth) for two commercially-available SLM devices used as active focal-plane phase masks in the visible regime (640 nm). It is shown that under ideal or realistic telescope aperture conditions, the contrast performance is negligibly affected in this bandwidth regime, reaching sufficient level for ground-based high-contrast imaging, which is typically dominated by atmospheric residuals.

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J. Kuhn and P. Patapis
Wed, 26 Oct 22
70/73

Comments: 15 pages, 5 figures

A resolution to the mystery of an etalon that is optically expanding and contracting at the same time [CL]

http://arxiv.org/abs/2210.10988


A white light illuminated etalon is a valuable resource for spectrograph calibration in radial velocity exoplanet detection, and other astronomical applications. These etalons benefit from low drift (${\sim} 10^{-11}$/day) and well-characterized stability of their mode structure. However, measurements of several etalon systems across bandwidths greater than $500$ nm indicate that the modes exhibit complex, wavelength-dependent drift. Surprisingly, modes in different regions of the spectrum were found to drift in different directions, implying that the optical length of the etalon is getting both longer and shorter at the same time. In this paper, we provide a solution to this puzzling observation. With Fresnel analysis and the transfer matrix method, we model the reflective phase of the multi-layer dielectric mirrors in the etalon used as a calibrator for the Habitable Zone Planet Finder (HPF). We use this phase to calculate the etalon mode positions and are able to reproduce the observed oscillatory chromatic drift of the etalon’s mode spectrum across 800-1300 nm. Despite the complexity of the mirror structure, our modeling indicates that the gradual relaxation of the outermost layers of the etalon mirrors is the dominant source of the observed behavior. We also model the effect of temperature, incident angle alignment variations, and manufacturing tolerances, and show that they are likely not causes of the chromatic mode frequency shifts. Our work highlights techniques that can be employed in the design of broad bandwidth mirrors for future etalons to make them more useful for the highest precision astronomical spectroscopy.

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M. Kreider, C. Fredrick, R. Terrien, et. al.
Fri, 21 Oct 22
4/76

Comments: 13 pages, 8 figures

Three-sided pyramid wavefront sensor. II. Preliminary demonstration on the new CACTI testbed [IMA]

http://arxiv.org/abs/2210.03823


The next generation of giant ground and space telescopes will have the light-collecting power to detect and characterize potentially habitable terrestrial exoplanets using high-contrast imaging for the first time. This will only be achievable if the performance of Giant Segmented Mirror Telescopes (GSMTs) extreme adaptive optics (ExAO) systems are optimized to their full potential. A key component of an ExAO system is the wavefront sensor (WFS), which measures aberrations from atmospheric turbulence. A common choice in current and next-generation instruments is the pyramid wavefront sensor (PWFS). ExAO systems require high spatial and temporal sampling of wavefronts to optimize performance, and as a result, require large detectors for the WFS. We present a closed-loop testbed demonstration of a three-sided pyramid wavefront sensor (3PWFS) as an alternative to the conventional four-sided pyramid wavefront (4PWFS) sensor for GSMT-ExAO applications on the new Comprehensive Adaptive Optics and Coronagraph Test Instrument (CACTI). The 3PWFS is less sensitive to read noise than the 4PWFS because it uses fewer detector pixels. The 3PWFS has further benefits: a high-quality three-sided pyramid optic is easier to manufacture than a four-sided pyramid. We detail the design of the two components of the CACTI system, the adaptive optics simulator and the PWFS testbed that includes both a 3PWFS and 4PWFS. A preliminary experiment was performed on CACTI to study the performance of the 3PWFS to the 4PWFS in varying strengths of turbulence using both the Raw Intensity and Slopes Map signal processing methods. This experiment was repeated for a modulation radius of 1.6 lambda/D and 3.25 lambda/D. We found that the performance of the two wavefront sensors is comparable if modal loop gains are tuned.

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L. Schatz, J. Codona, J. Long, et. al.
Tue, 11 Oct 22
72/92

Comments: 28 Pages, 15 Figures, and 4 Tables

Flattening laser frequency comb spectra with a high dynamic range, broadband spectral shaper on-a-chip [CL]

http://arxiv.org/abs/2210.01264


Spectral shaping is critical to many fields of science. In astronomy for example, the detection of exoplanets via the Doppler effect hinges on the ability to calibrate a high resolution spectrograph. Laser frequency combs can be used for this, but the wildly varying intensity across the spectrum can make it impossible to optimally utilize the entire comb, leading to a reduced overall precision of calibration. To circumvent this, astronomical applications of laser frequency combs rely on a bulk optic setup which can flatten the output spectrum before sending it to the spectrograph. Such flatteners require complex and expensive optical elements like spatial light modulators and have non-negligible bench top footprints. Here we present an alternative in the form of an all-photonic spectral shaper that can be used to flatten the spectrum of a laser frequency comb. The device consists of a circuit etched into a silicon nitride wafer that supports an arrayed-waveguide grating to disperse the light over hundreds of nanometers in wavelength, followed by Mach-Zehnder interferometers to control the amplitude of each channel, thermo-optic phase modulators to phase the channels and a second arrayed-waveguide grating to recombine the spectrum. The demonstrator device operates from 1400 to 1800 nm (covering the astronomical H band), with twenty 20 nm wide channels. The device allows for nearly 40 dBs of dynamic modulation of the spectrum via the Mach-Zehnders , which is greater than that offered by most spatial light modulators. With a superluminescent diode, we reduced the static spectral variation to ~3 dB, limited by the properties of the components used in the circuit and on a laser frequency comb we managed to reduce the modulation to 5 dBs, sufficient for astronomical applications.

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N. Jovanovic, P. Gatkine, B. Shen, et. al.
Wed, 5 Oct 22
43/73

Comments: 15 pages, 10 figures. arXiv admin note: substantial text overlap with arXiv:2209.09455

Investigation of dust grains by optical tweezers for space applications [IMA]

http://arxiv.org/abs/2210.01312


Cosmic dust plays a dominant role in the universe, especially in the formation of stars and planetary systems. Furthermore, the surface of cosmic dust grains is the bench-work where molecular hydrogen and simple organic compounds are formed. We manipulate individual dust particles in water solution by contactless and non-invasive techniques such as standard and Raman tweezers, to characterize their response to mechanical effects of light (optical forces and torques) and to determine their mineral compositions. Moreover, we show accurate optical force calculations in the T-matrix formalism highlighting the key role of composition and complex morphology in optical trapping of cosmic dust particles.This opens perspectives for future applications of optical tweezers in curation facilities for sample return missions or in extraterrestrial environments.

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A. Magazzù, D. Ciriza, A. Musolino, et. al.
Wed, 5 Oct 22
66/73

Comments: N/A

Achromatic design of a photonic tricoupler and phase shifter for broadband nulling interferometry [IMA]

http://arxiv.org/abs/2210.01040


Nulling interferometry is one of the most promising technologies for imaging exoplanets within stellar habitable zones. The use of photonics for carrying out nulling interferometry enables the contrast and separation required for exoplanet detection. So far, two key issues limiting current-generation photonic nullers have been identified: phase variations and chromaticity within the beam combiner. The use of tricouplers addresses both limitations, delivering a broadband, achromatic null together with phase measurements for fringe tracking. Here, we present a derivation of the transfer matrix of the tricoupler, including its chromatic behaviour, and our 3D design of a fully symmetric tricoupler, built upon a previous design proposed for the GLINT instrument. It enables a broadband null with symmetric, baseline-phase-dependent splitting into a pair of bright channels when inputs are in anti-phase. Within some design trade space, either the science signal or the fringe tracking ability can be prioritised. We also present a tapered-waveguide $180^\circ$-phase shifter with a phase variation of $0.6^\circ$ in the $1.4-1.7~\mu$m band, producing a near-achromatic differential phase between beams{ for optimal operation of the tricoupler nulling stage}. Both devices can be integrated to deliver a deep, broadband null together with a real-time fringe phase metrology signal.

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T. Klinner-Teo, M. Martinod, P. Tuthill, et. al.
Tue, 4 Oct 22
22/71

Comments: 20 pages, 17 figures, submitted to Journal of Astronomical Telescopes, Instruments, and Systems

Estimate of spot size of a flat top beam in detection of gravitational waves in space [IMA]

http://arxiv.org/abs/2210.00509


Motivated by the necessity of a high-quality stray light control in the detection of the gravitational waves in space, the spot size of a flat top beam generated by the clipping of the Gaussian beam(GB) is studied. By adopting the mode expansion method (MEM) approach to simulating the beam, a slight variant of the definition of the mean square deviation (MSD) spot size for the MEM beam is proposed and this enables us to quickly estimate the spot size for arbitrary propagation distance. Given that the degree of clipping is dependent on the power ratio within the surface of an optical element, the power ratio within the MSD spot range is used as a measure of spot size. The definition is then validated in the cases of simple astigmatic Gaussian beam and nearly-Gaussian beam profiles. As a representative example, the MSD spot size for a top-hat beam in a science interferometer in the detection of gravitational waves in space is then simulated. As in traditional MSD spot size analysis, the spot size is divergent when diffraction is taken into account. A careful error analysis is carried out on the divergence and in the present context, it is argued that this error will have little effect on our estimation. Using the results of our study allows an optimal design of optical systems with top-hat or other types of non-Gaussian beams. Furthermore, it allows testing the interferometry of space-based gravitational wave detectors for beam clipping in optical simulations. The present work will serve as a useful guide in the future system design of the optical bench and the sizes of the optical components.

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Z. Hao, T. Haase, H. Jin, et. al.
Tue, 4 Oct 22
61/71

Comments: 28 pages, 12 figures

An all-photonic, dynamic device for flattening the spectrum of a laser frequency comb for precise calibration of radial velocity measurements [IMA]

http://arxiv.org/abs/2209.09455


Laser frequency combs are fast becoming critical to reaching the highest radial velocity precisions. One shortcoming is the highly variable brightness of the comb lines across the spectrum (up to 4-5 orders of magnitude). This can result in some lines saturating while others are at low signal and lost in the noise. Losing lines to either of these effects reduces the precision and hence effectiveness of the comb. In addition, the brightness of the comb lines can vary with time which could drive comb lines with initially reasonable SNR’s into the two regimes described above. To mitigate these two effects, laser frequency combs use optical flattener’s.
Flattener’s are typically bulk optic setups that disperse the comb light with a grating, and then use a spatial light modulator to control the amplitude across the spectrum before recombining the light into another single mode fiber and sending it to the spectrograph. These setups can be large (small bench top), expensive (several hundred thousand dollars) and have limited stability. To address these issues, we have developed an all-photonic spectrum flattener on a chip. The device is constructed from optical waveguides on a SiN chip. The light from the laser frequency comb’s output optical fiber can be directly connected to the chip, where the light is first dispersed using an arrayed waveguide grating. To control the brightness of each channel, the light is passed through a Mach-Zehnder interferometer before being recombined with a second arrayed waveguide grating. Thermo-optic phase modulators are used in each channel before recombination to path length match the channels as needed.
Here we present the results from our first generation prototype. The device operates from 1400-1800 nm (covering the H band), with 20, 20 nm wide channels.

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N. Jovanovic, P. Gatkine, B. Shen, et. al.
Wed, 21 Sep 22
23/68

Comments: 7 pages, 5 figures, conference

BER Performance of Photon Counting PPM vs. DPSK for Satellite Communications [CL]

http://arxiv.org/abs/2209.06161


Expressions for the BER of M-ary PPM & biphase DPSK modulations in the presence of noise are derived using analytical, statistical methods. The PPM expression is verified via Poisson statistics based simulation. BER expressions are then applied to a representative set of receiving telescope & sky spectral radiance parameters in order to assess performance of PPM & DPSK relative to one another. Finally, efficiency & additional considerations are discussed.

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D. Paulson
Wed, 14 Sep 22
83/90

Comments: Final report for PhD student independent study. Contains novel derivations on uncoded bit error rate for pulse position modulation (PPM) on optical links

Joint optimization of wavefront sensing and reconstruction with automatic differentiation [IMA]

http://arxiv.org/abs/2209.05904


High-contrast imaging instruments need extreme wavefront control to directly image exoplanets. This requires highly sensitive wavefront sensors which optimally make use of the available photons to sense the wavefront. Here, we propose to numerically optimize Fourier-filtering wavefront sensors using automatic differentiation. First, we optimize the sensitivity of the wavefront sensor for different apertures and wavefront distributions. We find sensors that are more sensitive than currently used sensors and close to the theoretical limit, under the assumption of monochromatic light. Subsequently, we directly minimize the residual wavefront error by jointly optimizing the sensing and reconstruction. This is done by connecting differentiable models of the wavefront sensor and reconstructor and alternatingly improving them using a gradient-based optimizer. We also allow for nonlinearities in the wavefront reconstruction using Convolutional Neural Networks, which extends the design space of the wavefront sensor. Our results show that optimization can lead to wavefront sensors that have improved performance over currently used wavefront sensors. The proposed approach is flexible, and can in principle be used for any wavefront sensor architecture with free design parameters.

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R. Landman, C. Keller, E. Por, et. al.
Wed, 14 Sep 22
87/90

Comments: SPIE Astronomical Telescopes and Instrumentation 2022

The crossed-sine wavefront sensor: first tests and results [CL]

http://arxiv.org/abs/2209.00829


The crossed-sine wavefront sensor (WFS) is a pupil plane wavefront sensor that measures the first derivatives of the wavefront. It is made by three main components: a gradient transmission filter (GTF) built from a product of sine functions rotated by 45 degrees around the optical axis, a 2×2 mini-lens array (MLA) at the focus of the tested optical system and a detector array located on a plane conjugated to the pupil. The basic principle consists in acquiring four pupil images simultaneously, each image being observed from different points located behind the GTF. After the simulation work which demonstrated the wavefront reconstruction capability, we are now in the phase of implementation of the prototype in the lab. The crossed-sine WFS could achieve a simultaneous high spatial resolution at the pupil of the tested optics and absolute measurement accuracy comparable to that attained by laser-interferometers. In this paper we introduce seven customized phase masks and make measurements of them.First tests and resultsare demonstrated, based on which we explore the performance of our crossed-sine WFS and make comparisons with that of the laser-interferomete

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L. Schreiber, Y. Feng, A. Spang, et. al.
Mon, 5 Sep 22
16/53

Comments: N/A

The crossed-sine wavefront sensor: first tests and results [CL]

http://arxiv.org/abs/2209.00829


The crossed-sine wavefront sensor (WFS) is a pupil plane wavefront sensor that measures the first derivatives of the wavefront. It is made by three main components: a gradient transmission filter (GTF) built from a product of sine functions rotated by 45 degrees around the optical axis, a 2×2 mini-lens array (MLA) at the focus of the tested optical system and a detector array located on a plane conjugated to the pupil. The basic principle consists in acquiring four pupil images simultaneously, each image being observed from different points located behind the GTF. After the simulation work which demonstrated the wavefront reconstruction capability, we are now in the phase of implementation of the prototype in the lab. The crossed-sine WFS could achieve a simultaneous high spatial resolution at the pupil of the tested optics and absolute measurement accuracy comparable to that attained by laser-interferometers. In this paper we introduce seven customized phase masks and make measurements of them.First tests and resultsare demonstrated, based on which we explore the performance of our crossed-sine WFS and make comparisons with that of the laser-interferomete

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L. Schreiber, Y. Feng, A. Spang, et. al.
Mon, 5 Sep 22
13/53

Comments: N/A

Laue and Fresnel lenses [IMA]

http://arxiv.org/abs/2208.12362


The low-energy gamma-ray domain is an important window for the study of the high energy Universe. Here matter can be observed in extreme physical conditions and during powerful explosive events. However, observing gamma-rays from faint sources is extremely challenging with current instrumentation. With techniques used at present collecting more signal requires larger detectors, leading to an increase in instrumental background. For the leap in sensitivity that is required for future gamma-ray missions use must be made of flux concentrating telescopes. Fortunately, gamma-ray optics such as Laue or Fresnel lenses, based on diffraction, make this possible. Laue lenses work with moderate focal lengths (tens to a few hundreds of metres), but provide only rudimentary imaging capabilities. On the other hand, Fresnel lenses offer extremely good imaging, but with a very small field of view and a requirement for focal lengths $\sim$10$^8$ m. This chapter presents the basic concepts of these optics and describes their working principles, their main properties and some feasibility studies already conducted.

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E. Virgilli, H. Halloin and G. Skinner
Mon, 29 Aug 22
31/49

Comments: 43 pages, 17 Figures – accepted Chapter for publication in the Section “Optics and Detectors for Gamma-ray Astrophysics” of the “Handbook of X-ray and Gamma-ray Astrophysics” by Springer – Editors in chief: C. Bambi and A. Santangelo

Super-resolution wavefront reconstruction [IMA]

http://arxiv.org/abs/2208.12052


Super-Resolution (SR) is a technique that seeks to upscale the resolution of a set of measured signals. SR retrieves higher-frequency signal content by combining multiple lower resolution sampled data sets. SR is well known both in the temporal and spatial domains. It is widely used in imaging to reduce aliasing and enhance the resolution of coarsely sampled images.This paper applies the SR technique to the bi-dimensional wavefront reconstruction. In particular, we show how SR is intrinsically suited for tomographic multi WaveFront Sensor (WFS) AO systems revealing many of its advantages with minimal design effort. This paper provides a direct space and Fourier-optics description of the wavefront sensing operation and demonstrate how SR can be exploited through signal reconstruction, especially in the framework of Periodic Nonuniform Sampling. Both meta uniform and nonuniform sampling schemes are investigated. Then, the SR bi-dimensional model for a Shack Hartmann (SH) WFS is provided and the characteristics of the sensitivity function are analyzed. The SR concept is finally validated with numerical simulations of representative multi WFS SH AO systems. Our results show that combining several WFS samples in a SR framework grants access to a larger number of modes than the native one offered by a single WFS and that despite the fixed sub-aperture size across samples. Furthermore, we show that the associated noise propagation is not degraded under SR. Finally, the concept is extended to the signal produced by single Pyramid WFS. In conclusion, SR applied to wavefront reconstruction offers a new parameter space to explore as it decouples the size of the subaperture from the desired wavefront sampling resolution. By cutting short with old assumptions, new, more flexible and better performing AO designs become now possible.

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S. Oberti, C. Correia, T. Fusco, et. al.
Fri, 26 Aug 22
43/49

Comments: Astronomy & Astrophysics Section: 13. Astronomical instrumentation AA/2022/43954

Focal-plane wavefront sensing with photonic lanterns I: theoretical framework [IMA]

http://arxiv.org/abs/2208.10563


The photonic lantern (PL) is a tapered waveguide that can efficiently couple light into multiple single-mode optical fibers. Such devices are currently being considered for a number of tasks, including the coupling of telescopes and high-resolution, fiber-fed spectrometers, coherent detection, nulling interferometry, and vortex-fiber nulling (VFN). In conjunction with these use cases, PLs can simultaneously perform low-order focal-plane wavefront sensing. In this work, we provide a mathematical framework for the analysis of the photonic lantern wavefront sensor (PLWFS), deriving linear and higher-order reconstruction models as well as metrics through which sensing performance — both in the linear and nonlinear regimes — can be quantified. This framework can be extended to account for additional optics such as beam-shaping optics and vortex masks, and is generalizable to other wavefront sensing architectures. Lastly, we provide initial numerical verification of our mathematical models, by simulating a 6-port PLWFS. In a companion paper, we provide a more comprehensive numerical characterization of few-port PLWFSs, and consider how the sensing properties of these devices can be controlled and optimized.

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J. Lin, M. Fitzgerald, Y. Xin, et. al.
Wed, 24 Aug 22
10/67

Comments: Accepted to JOSA B

Swarm of lightsail nanosatellites for Solar System exploration [CL]

http://arxiv.org/abs/2208.10980


This paper presents a study for the realization of a space mission which employs nanosatellites driven by an external laser source impinging on an optimized lightsail, as a valuable technology to launch swarms of spacecrafts into the Solar System. Nanosatellites propelled by laser can be useful for the heliosphere exploration and for planetary observation, if suitably equipped with sensors, or be adopted for the establishment of network systems when placed into specific orbits. By varying the area-to-mass ratio (i.e., the ratio between the sail area and the payload weight) and the laser power, it is possible to insert the spacecraft into different hyperbolic orbits with respect to Earth, thus reaching the target by means of controlled trajectories in a relatively short amount of time. A mission involving nanosatellites of the order of 1 kg of mass is envisioned, by describing all the on-board subsystems and satisfying all the requirements in term of power and mass budget. Particular attention is paid to the telecommunication subsystem, which must offer all the necessary functionalities. To fabricate the lightsail, the thin films technology has been considered, by verifying the sail thermal stability during the thrust phase. Moreover, the problem of mechanical stability of the lightsail has been tackled, showing that the distance between the ligthsail structure and the payload plays a pivotal role. Some potential applications of the proposed technology are discussed, such as the mapping of the heliospheric environment.

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G. Santi, A. Corso, D. Garoli, et. al.
Wed, 24 Aug 22
62/67

Comments: N/A

Experimental Trials With The Optical Differentiation Wavefront Sensor For Extended Objects [IMA]

http://arxiv.org/abs/2208.08520


Commonly used wavefront sensors, the Shack Hartmann wavefront sensor and the pyramid wavefront sensor, for example, have large dynamic range or high sensitivity, trading one regime for the other. A new type of wavefront sensor is being developed and is currently undergoing testing at the University of Arizona’s Center for Astronomical Adaptive Optics. This sensor builds on linear optical differentiation theory by using linear, spatially varying halfwave plates in an intermediate focal plane. These filters, along with the polarizing beam splitters, divide the beam into four pupil images, similar to those produced by the pyramid wavefront sensor. The wavefront is then reconstructed from the local wavefront slope information contained in these images. The ODWFS is ideally suited for wavefront sensing on extended objects because of its large dynamic range and because it operates in a pupil plane which allows for on chip resampling even for arbitrarily shaped sources. We have assembled the ODWFS on a testbed using 32 by 32 square 1000 actuator deformable mirror to introduce aberration into a simulated telescope beam. We are currently testing the system’s spatial frequency response and are comparing the resulting data to numerical simulations. This paper presents the results of these initial experiments.

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M. O’Brien, S. Haffert, J. Long, et. al.
Fri, 19 Aug 22
28/55

Comments: SPIE Astronomical Telescopes and Instrumentation, 2022 Proceeding 12185-55

Experimental observation of violent relaxation and the formation of out-of-equilibrium quasi-stationary states [CL]

http://arxiv.org/abs/2205.10948


Large scale structures in the Universe, ranging from globular clusters to entire galaxies, are the manifestation of relaxation to out-of-equilibrium states that are not described by standard statistical mechanics at equilibrium. Instead, they are formed through a process of a very different nature, i.e. violent relaxation. However, astrophysical time-scales are so large that it is not possible to directly observe these relaxation dynamics and therefore verify the details of the violent relaxation process. We develop a table-top experiment and model that allows us to directly observe effects such as mixing of phase space, and violent relaxation, leading to the formation of a table-top analogue of a galaxy. The experiment allows us to control a range of parameters, including the nonlocal (gravitational) interaction strength and quantum effects, thus providing an effective test-bed for gravitational models that cannot otherwise be directly studied in experimental settings.

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M. Lovisetto, M. Braidotti, R. Prizia, et. al.
Tue, 24 May 22
44/92

Comments: 7 pages, 5 figures; Supplementary Information 9 pages and 7 figures

A Novel Solution for Resonant Scattering Using Self-Consistent Boundary Conditions [IMA]

http://arxiv.org/abs/2205.05082


We present two novel additions to the semi-analytic solution of Lyman $\alpha$ (Ly$\alpha$) radiative transfer in spherical geometry: (1) implementation of the correct boundary condition for a steady source, and (2) solution of the time-dependent problem for an impulsive source. For the steady-state problem, the solution can be represented as a sum of two terms: a previously-known analytic solution of the equation with mean intensity $J=0$ at the surface, and a novel, semi-analytic solution which enforces the correct boundary condition of zero-ingoing intensity at the surface. This solution is compared to that of the Monte Carlo method, which is valid at arbitrary optical depth. It is shown that the size of the correction is of order unity when the spectral peaks approach the Doppler core and decreases slowly with line center optical depth, specifically as $(a \tau_0)^{-1/3}$, which may explain discrepancies seen in previous studies. For the impulsive problem, the time, spatial, and frequency dependence of the solution are expressed using an eigenfunction expansion in order to characterize the escape time distribution and emergent spectra of photons. It is shown that the lowest-order eigenfrequency agrees well with the decay rate found in the Monte Carlo escape time distribution at sufficiently large line-center optical depths. The characterization of the escape-time distribution highlights the potential for a Monte Carlo acceleration method, which would sample photon escape properties from distributions rather than calculating every photon scattering, thereby reducing computational demand.

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B. McClellan, S. Davis and P. Arras
Thu, 12 May 22
60/63

Comments: 23 pages, 10 figures, 2 appendices, resubmitted to ApJ after review

Regimes in astrophysical lensing: refractive optics, diffractive optics, and the Fresnel scale [HEAP]

http://arxiv.org/abs/2204.12004


Astrophysical lensing has typically been studied in two regimes: diffractive optics and refractive optics. Diffractive optics is characterized by a perturbative expansion of the Kirchhoff-Fresnel diffraction integral, while refractive optics is characterized by the stationary phase approximation. Previously, it has been assumed that the Fresnel scale, $R_F$ , is the relevant physical scale that separates these two regimes. With the recent introduction of Picard-Lefschetz theory to the field of lensing, it has become possible to generalize the refractive description of discrete images to all wave parameters, and, in particular, exactly evaluate the diffraction integral at all frequencies. In this work, we assess the regimes of validity of refractive and diffractive approximations for a simple one-dimensional lens model through comparison with this exact evaluation. We find that, contrary to previous assumptions, the true separation scale between these regimes is given by $R_F / \sqrt{\kappa}$, where $\kappa$ is the convergence of the lens. Thus, when the lens is strong, refractive optics can hold for arbitrarily small scales. We also argue that intensity variations in diffractive optics are generically small, which has implications for the study of strong diffractive scintillation (DISS).

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D. Jow, U. Pen and J. Feldbrugge
Wed, 27 Apr 22
60/68

Comments: 15 pages, 8 figures

Adaptive hyperspectral imaging using structured illumination in a spatial light modulator-based interferometer [CL]

http://arxiv.org/abs/2204.10587


We develop a novel hyperspectral imaging system using structured illumination in an SLM-based Michelson interferometer. In our design, we use a reflective SLM as a mirror in one of the arms of a Michelson interferometer, and scan the interferometer by varying the phase across the SLM display. For achieving the latter, we apply a checkerboard phase mask on the SLM display where the gray value varies between 0-255, thereby imparting a dynamic phase of up to 262{\deg} to the incident light beam. We couple a supercontinuum source into the interferometer in order to mimic an astronomical object such as the Sun, and choose a central wavelength of 637.4 nm akin to the strong emission line of Fe X present in the solar spectrum. We use a bandwidth of 30 nm, and extract fringes corresponding to a spectral resolution of 3.8 nm which is limited by the reflectivity of the SLM. We also demonstrate a maximum wavelength tunability of ~8 nm by varying the phase over the phase mask with a spectral sampling of around 0.03 nm between intermediate fringes. The checkerboard phase mask can be adapted close to real time on time-scales of a few tens of milliseconds to obtain spectral information for other near-contiguous wavelengths. The compactness, potential low cost, low power requirements, real-time tunability and lack of moving mechanical parts in the setup implies that it can have very useful applications in settings which require near real-time, multi-wavelength spectroscopic applications, and is especially relevant in space astronomy.

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A. Chandra, M. Karmakar, D. Nandy, et. al.
Mon, 25 Apr 22
9/36

Comments: 14 pages, 8 figures, accepted for publication in Optics Express

Dynamics of Optically-Trapped High-Aspect-Ratio $β$-NaYF Hexagonal Prisms — Towards kHz-MHz Gravitational Wave Searches [CL]

http://arxiv.org/abs/2204.10843


We present experimental results on optical trapping of Yb-doped $\beta-$NaYF sub-wavelength-thickness high-aspect-ratio hexagonal prisms with a micron-scale radius. The prisms are trapped in vacuum using an optical standing wave, oriented with the normal vector to their face along the beam propagation direction, and exhibit characteristic modes of three translational and two torsional degrees of freedom. The measured motional spectra are compared with numerical simulations. This plate-like geometry simultaneously enables trapping with low photon-recoil-heating, high mass, and high trap frequency, potentially leading to advances in high frequency gravitational wave searches in the Levitated Sensor Detector (LSD), currently under construction. The material used here has previously been shown to exhibit internal cooling via laser refrigeration when optically trapped and illuminated with light of suitable wavelength. Employing such laser refrigeration methods in the context of our work may enable higher trapping intensity thus and higher trap frequencies for gravitational wave searches approaching the several hundred kHz range.

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G. Winstone, Z. Wang, S. Klomp, et. al.
Mon, 25 Apr 22
29/36

Comments: N/A

Imaging stars with quantum error correction [CL]

http://arxiv.org/abs/2204.06044


The development of high-resolution, large-baseline optical interferometers would revolutionize astronomical imaging. However, classical techniques are hindered by physical limitations including loss, noise, and the fact that the received light is generally quantum in nature. We show how to overcome these issues using quantum communication techniques. We present a general framework for using quantum error correction codes for protecting and imaging starlight received at distant telescope sites. In our scheme, the quantum state of light is coherently captured into a non-radiative atomic state via Stimulated Raman Adiabatic Passage, which is then imprinted into a quantum error correction code. The code protects the signal during subsequent potentially noisy operations necessary to extract the image parameters. We show that even a small quantum error correction code can offer significant protection against noise. For large codes, we find noise thresholds below which the information can be preserved. Our scheme represents an application for near-term quantum devices that can increase imaging resolution beyond what is feasible using classical techniques.

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Z. Huang, G. Brennen and Y. Ouyang
Thu, 14 Apr 22
56/62

Comments: 8 pages, 5 figures, comments are welcome

Short review on the refractive index of air as a function of temperature, pressure, humidity and ionization [CL]

http://arxiv.org/abs/2204.02603


The empirical law of Gladstone-Dale is insufficient for high-precision studies using the refractivity of a gas: this is not exactly proportional to its density, and the gas may not be properly described as perfect. An optical Mariotte temperature allows making a comparative analysis of the results given by various authors. The effect of hygrometry on the refractivity at visible wavelengths is historically traced and its small effect on the astronomical refraction angle numerically shown. Finally at infrared and radio wavelengths, the effects of the humidity in the lower atmosphere can be strong; as for the ionosphere, its curvature plays an essential role for the astronomical refraction angle unlike in the visible.

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L. Dettwiller
Thu, 7 Apr 22
28/45

Comments: in French

Properties of optical ducts, their chromatism and its effects on astronomical refraction [CL]

http://arxiv.org/abs/2204.02605


The fundamental quadrature governing light rays in a spherically symmetrical medium is first recalled. A rigorous discussion of some qualitative properties of its solutions follows, using the Young-Kattawar diagram which leads to a geometric formulation of the ray curvature. The case of an optical duct is deepened, analyzing transfer curves for different positions of the observer with respect to the duct. New analytical expressions for their wavelength dependence are derived, and their numerical consequences are coherent with computer simulations.

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L. Dettwiller
Thu, 7 Apr 22
32/45

Comments: in French

Computation of Optical Refractive Index Structure Parameter from its Statistical Definition Using Radiosonde Data [CL]

http://arxiv.org/abs/2204.00349


Knowledge of the optical refractive index structure parameter $C_n^2$ is of interest for Free Space Optics (FSO) and ground-based optical astronomy, as it depicts the strength of the expected scintillation on the received optical waves. Focus is given here to models using meteorological quantities coming from radiosonde measurements as inputs to estimate the $C_n^2$ profile in the atmosphere. A model relying on the $C_n^2$ statistical definition is presented and applied to recent high-density radiosonde profiles at Trappes (France) and Hilo, HI (USA). It is also compared to thermosonde measurements coming from the T-REX campaign. This model enables to obtain site-specific average profiles and to identify isolated turbulent layers using only pressure and temperature measurements, paving the way for optical site selection.

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F. Quatresooz, D. Vanhoenacker-Janvier and C. Oestges
Mon, 4 Apr 22
36/50

Comments: N/A

Simulating the Study of Exoplanets Using Photonic Spectrographs [IMA]

http://arxiv.org/abs/2203.10153


Photonic spectrographs offer a highly miniaturized, flexible, and stable on-chip solution for astronomical spectroscopy and can be used for various science cases such as determining the atmospheric composition of exoplanets to understand their habitability, formation, and evolution. Arrayed Waveguide Gratings (AWGs) have shown the best promise to be used as an astrophotonic spectrograph. We developed a publically-available tool to conduct a preliminary examination of the capability of the AWGs in spectrally resolving exoplanet atmospheres. We derived the Line-Spread-Function (LSF) as a function of wavelength and the Full-Width-at-Half-Maximum (FWHM) of the LSF as a function of spectral line width to evaluate the response of a discretely- and continuously-sampled low-resolution AWG (R $\sim$ 1000). We observed that the LSF has minimal wavelength dependence ($\sim$5\%), irrespective of the offset with respect to the center-wavelengths of the AWG channels, contrary to the previous assumptions. We further confirmed that the observed FWHM scales linearly with the emission line width. Finally, we present simulated extraction of a sample molecular absorption spectrum with the discretely- and continuously-sampled low-resolution AWGs. From this, we show that while the discrete AWG matches its expected resolving power, the continuous AWG spectrograph can, in principle, achieve an effective resolution significantly greater ($\sim$ 2x) than the discrete AWG. This detailed examination of the AWGs will be foundational for future deployment of AWG spectrographs for astronomical science cases such as exoplanet atmospheres.

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M. Perez, P. Gatkine, N. Jovanovic, et. al.
Tue, 22 Mar 22
46/82

Comments: 13 pages, 6 figures, Presented at and published in the proceedings of SPIE Photonics West 2022

Thermal-light heterodyne spectroscopy with frequency comb calibration [CL]

http://arxiv.org/abs/2108.05991


Precision laser spectroscopy is key to many developments in atomic and molecular physics and the advancement of related technologies such as atomic clocks and sensors. However, in important spectroscopic scenarios, such as astronomy and remote sensing, the light is of thermal origin and interferometric or diffractive spectrometers typically replace laser spectroscopy. In this work, we employ laser-based heterodyne radiometry to measure incoherent light sources in the near-infrared and introduce techniques for absolute frequency calibration with a laser frequency comb. Measuring the solar continuum, we obtain a signal-to-noise ratio that matches the fundamental quantum-limited prediction given by the thermal photon distribution and our system’s efficiency, bandwidth, and averaging time. With resolving power R~1,000,000 we determine the center frequency of an iron line in the solar spectrum to sub-MHz absolute frequency uncertainty in under 10 minutes, a fractional precision 1/4000 the linewidth. Additionally, we propose concepts that take advantage of refractive beam shaping to decrease the effects of pointing instabilities by 100x, and of frequency comb multiplexing to increase data acquisition rates and spectral bandwidths by comparable factors. Taken together, our work brings the power of telecommunications photonics and the precision of frequency comb metrology to laser heterodyne radiometry, with implications for solar and astronomical spectroscopy, remote sensing, and precise Doppler velocimetry.

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C. Fredrick, F. Olsen, R. Terrien, et. al.
Tue, 8 Mar 22
6/100

Comments: 16 pages, 9 figures. Revised

Computation of the lateral shift due to atmospheric refraction [IMA]

http://arxiv.org/abs/2203.03459


Atmospheric refraction modifies the apparent position of objects in the sky. We computed the lateral translation that is to be considered for short-range applications, such as wavefront sensing and meteor trajectories. We aim to calculate the lateral shift at each altitude and study its variation according to meteorological conditions and the location of the observation site. We also pay special attention to the chromatism of this lateral shift. We extracted the variation equations of refraction from the geometric tracing of a light ray path. A numerical method and a dry atmosphere model allowed us to numerically integrate the system of coupled equations. In addition to this, based on Taylor expansions, we established three analytic approximations of the lateral shift, one of which is the one already known in the literature. We compared the three approximations to the numerical solution. All these estimators are included in a Python 3.2 package, which is available online. Using the numerical integration estimator, we calculated the lateral shift values for any zenith angle including low elevations. The shift is typically around 3 m at a zenith angle of 45{\deg}, 10 m at 65{\deg}, and even 300 m{\deg} at 85{\deg}. Next, the study of the variability of the lateral shift as a function of wavelength shows differences of up to 2% between the visible and near infrared. The analysis of the errors of each approximation shows the ranges of validity of the three estimators as a function of the zenith angle. The flat Earth estimator achieves a relative error of less than 1% up to 55{\deg} while the new extended second-order estimators improves this result up to 75{\deg}. The flat Earth estimator is sufficient for applications where the zenith angle is below 55{\deg} but a refined estimator is necessary to estimate meteor trajectories at low elevations.

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H. Labriji, O. Herscovici-Schiller and F. Cassaing
Tue, 8 Mar 22
52/100

Comments: Reproduced with permission from Astronomy & Astrophysics, Copyright ESO

Recommended high performance telescope system design for the TianQin project [CL]

http://arxiv.org/abs/2202.11378


China is planning to construct a new space-borne gravitational-wave (GW) observatory, the TianQin project, in which the spaceborne telescope is an important component in laser interferometry. The telescope is aimed to transmit laser beams between the spacecrafts for the measurement of the displacements between proof-masses in long arms. The telescope should have ultra-small wavefront deviation to minimize noise caused by pointing error, ultra-stable structure to minimize optical path noise caused by temperature jitter, ultra-high stray light suppression ability to eliminate background noise. In this paper, we realize a telescope system design with ultra-stable structure as well as ultra-low wavefront distortion for the space-based GW detection mission. The design requirements demand extreme control of high image quality and extraordinary stray light suppression ability. Based on the primary aberration theory, the initial structure design of the mentioned four-mirror optical system is explored. After optimization, the maximum RMS wavefront error is less than lamda/300 over the full field of view (FOV), which meets the noise budget on the telescope design. The stray light noise caused by the back reflection of the telescope is also analyzed. The noise at the position of optical bench is less than 10-10 of the transmitted power, satisfying the requirements of space gravitational-wave detection. We believe that our design can be a good candidate for TianQin project, and can also be a good guide for the space telescope design in any other similar science project.

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Z. Fan, L. Zhao, J. Peng, et. al.
Thu, 24 Feb 22
44/52

Comments: N/A

Crosstalk in image plane beam combination for optical interferometers [IMA]

http://arxiv.org/abs/2202.00692


Image plane beam combination in optical interferometers multiplexes the interference fringes from multiple baselines onto a single detector. The beams of starlight are arranged in a non-redundant pattern at the entrance of the combiner so that the signal from each baseline can be separated from one another in the frequency domain. If the signals from different baselines overlap in the frequency domain, this can give rise to a systematic error in the fringe measurements known as baseline crosstalk. In this paper we quantify crosstalk arising from the combination of atmospheric seeing and beam propagation over distances of order hundreds of metres. We find that in idealised conditions atmospheric wavefront errors and beam propagation do not contribute to crosstalk. However, when aperture stops are included in the optical beam train we observe that wavefront errors can result in squared visibility errors arising from crosstalk as high as $\Delta V^{2} = 6.6\times10^{-3}$ under realistic observing conditions.

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D. Mortimer and D. Buscher
Thu, 3 Feb 22
4/56

Comments: 15 pages, 23 figures, accepted for publication in MNRAS

Analysis of performance and robustness against jitter of various search methods for acquiring optical links in space [CL]

http://arxiv.org/abs/2202.00784


We discuss various methods for acquiring optical links in space using a dedicated acquisition sensor. Statistical models are developed and simple analytical equations derived that compare the performance between a single and dual spiral scan approach as well as between sequential and parallel acquisition of link chains. Simple derived analytical equations allow relating essential search parameters such as track width, variance of the uncertainty distribution, capture radius and scan speed to the probabilities of acquiring the links within a specific time. We also assess the probability of failing to acquire a link due to beam jitter and derive a simple analytical model that allows determining the maximum tolerable jitter for a given beam overlap and required probability of success. All results are validated by Monte Carlo simulations and applied to the concrete example of the GRACE FO mission.

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G. Hechenblaikner
Thu, 3 Feb 22
16/56

Comments: 11 pages, two column format, 9pt font

Non-linear interaction of laser light with vacuum: contributions to the energy density and pressure in presence of an intense magnetic field [CL]

http://arxiv.org/abs/2201.11098


Recent simulations show that very large electric and magnetic fields near the kilo Tesla strength will likely be generated by ultra-intense lasers at existing facilities over distances of hundreds of microns in underdense plasmas. Stronger ones are even expected in the future although some technical dificulties must be overcome. In addition, it has been shown that vacuum exhibits a peculiar non-linear behaviour in presence of high magnetic and electric field strengths. In this work we are interested in the analysis of thermodynamical contributions of vacuum to the energy density and pressure when radiation interacts with it in the presence of an external magnetic field. Using the Euler-Heisenberg formalism in the regime of weak fields i.e. smaller than critical Quantum Electrodynamics field strength values, we evaluate these magnitudes and analyze the highly anisotropic behaviour we find. Our work has implications for photon-photon scattering with lasers and astrophysically magnetized underdense systems far outside their surface where matter effects are increasingly negligible.

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M. Pérez-García, A. Martínez and E. Querts
Thu, 27 Jan 22
19/44

Comments: 7 pages, 3 figures. Invited contribution article. Accepted in Plasma Physics and Controlled Fusion

High speed, high power 2D beam steering for mitigation of optomechanical parametric instability in gravitational wave detectors [CL]

http://arxiv.org/abs/2201.08272


In this paper we propose a novel strategy to control optomechanical parametric instability (PI) in gravitational wave (GW) detectors, based on radiation pressure. The fast deflection of a high power beam is the key element of our approach. We built a 2D deflection system based on a pair of acousto-optic modulators (AOMs) that combines high rapidity and large scan range. As fast frequency switching configurable AOM driver we used an Universal Software Radio Peripheral (USRP) combined with a high performance personal computer (PC). In this way we demonstrate a 2D beam steering system with flat efficiency over the whole scan range and with a transition time of 50 ns between two arbitrary consecutive deflection positions for a beam power of 3.6 W.

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T. Harder, M. Turconi, R. Soulard, et. al.
Fri, 21 Jan 22
25/60

Comments: N/A

Geometric tilt-to-length coupling in precision interferometry: mechanisms and analytical descriptions [CL]

http://arxiv.org/abs/2201.06943


Tilt-to-length coupling is a technical term for the cross-coupling of angular or lateral jitter into an interferometric phase signal. It is an important noise source in precision interferometers and originates either from changes in the optical path lengths or from wavefront and clipping effects. Within this paper, we focus on geometric TTL coupling and categorize it into a number of different mechanisms for which we give analytic expressions. We then show that this geometric description is not always sufficient to predict the TTL coupling noise within an interferometer. We, therefore, discuss how understanding the geometric effects allows TTL noise reduction already by smart design choices. Additionally, they can be used to counteract the total measured TTL noise in a system. The presented content applies to a large variety of precision interferometers, including space gravitational wave detectors like LISA.

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M. Hartig, S. Schuster and G. Wanner
Wed, 19 Jan 22
48/121

Comments: N/A

Observing the optical modes of parametric instability [CL]

http://arxiv.org/abs/2201.05276


Parametric Instability (PI) is a phenomenon that results from resonant interactions between optical and acoustic modes of a laser cavity. This is problematic in gravitational wave interferometers where the high intra-cavity power and low mechanical loss mirror suspension systems create an environment where three mode PI will occur without intervention. We demonstrate a technique for real time imaging of the amplitude and phase of the optical modes of PI yielding the first ever images of this phenomenon which could form part of active control strategies for future detectors.

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M. Schiworski, V. Bossilkov, C. Blair, et. al.
Mon, 17 Jan 22
12/59

Comments: 4 pages, 4 figures. Pre-submission version

Observing the optical modes of parametric instability [CL]

http://arxiv.org/abs/2201.05276


Parametric Instability (PI) is a phenomenon that results from resonant interactions between optical and acoustic modes of a laser cavity. This is problematic in gravitational wave interferometers where the high intra-cavity power and low mechanical loss mirror suspension systems create an environment where three mode PI will occur without intervention. We demonstrate a technique for real time imaging of the amplitude and phase of the optical modes of PI yielding the first ever images of this phenomenon which could form part of active control strategies for future detectors.

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M. Schiworski, V. Bossilkov, C. Blair, et. al.
Mon, 17 Jan 22
3/59

Comments: 4 pages, 4 figures. Pre-submission version

Demonstration of magnetic and light-controlled actuation of a photomagnetically actuated deformable mirror for wavefront control [IMA]

http://arxiv.org/abs/2112.12813


Deformable Mirrors (DMs) have wide applications ranging from astronomical imaging to laser communications and vision science. However, they often require bulky multi-channel cables for delivering high power to their drive actuators. A low powered DM which is driven in a contactless fashion could provide a possible alternative to this problem.Here, we present a photo-magnetically actuated deformable mirror (PMADM) concept which is actuated in a contactless fashion by a permanent magnet and low power laser heating source. This paper presents the laboratory demonstration of prototype optical surface quality, magnetic control of focus, and COMSOL simulations of its precise photo-control. The PMADM prototype is made of a magnetic composite (polydimethylsiloxane [PDMS] + ferromagnetic $\text{CrO}_\text{2}$) and an optical-quality substrate layer and is 30.48 mm $\times$ 30.48 mm $\times$ 175 $\mu$ m in dimension with an optical pupil diameter of 8 mm. It deforms to 5.76 $\mu$ m when subjected to a 0.12 T magnetic flux density and relaxes to 3.76 $\mu$ m when illuminated by a 50 mW laser. A maximum stroke of 8.78 $\mu$ m before failure is also estimated considering a 3x safety factor. This works also includes simulation of astigmatism generation with the PMADM, a first step in demonstrating control of higher order modes. A fully developed PMADM can have potential application for wavefront corrections in vacuum and space environments.

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A. Jha, E. Douglas, M. Li, et. al.
Tue, 28 Dec 21
19/55

Comments: 19 pages, 18 figures

Demonstration of magnetic and light-controlled actuation of a photomagnetically actuated deformable mirror for wavefront control [IMA]

http://arxiv.org/abs/2112.12813


Deformable Mirrors (DMs) have wide applications ranging from astronomical imaging to laser communications and vision science. However, they often require bulky multi-channel cables for delivering high power to their drive actuators. A low powered DM which is driven in a contactless fashion could provide a possible alternative to this problem.Here, we present a photo-magnetically actuated deformable mirror (PMADM) concept which is actuated in a contactless fashion by a permanent magnet and low power laser heating source. This paper presents the laboratory demonstration of prototype optical surface quality, magnetic control of focus, and COMSOL simulations of its precise photo-control. The PMADM prototype is made of a magnetic composite (polydimethylsiloxane [PDMS] + ferromagnetic $\text{CrO}_\text{2}$) and an optical-quality substrate layer and is 30.48 mm $\times$ 30.48 mm $\times$ 175 $\mu$ m in dimension with an optical pupil diameter of 8 mm. It deforms to 5.76 $\mu$ m when subjected to a 0.12 T magnetic flux density and relaxes to 3.76 $\mu$ m when illuminated by a 50 mW laser. A maximum stroke of 8.78 $\mu$ m before failure is also estimated considering a 3x safety factor. This works also includes simulation of astigmatism generation with the PMADM, a first step in demonstrating control of higher order modes. A fully developed PMADM can have potential application for wavefront corrections in vacuum and space environments.

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A. Jha, E. Douglas, M. Li, et. al.
Tue, 28 Dec 21
46/55

Comments: 19 pages, 18 figures

Experimental verification of inter-satellite clock synchronization at LISA performance levels [IMA]

http://arxiv.org/abs/2112.12586


The Laser Interferometer Space Antenna (LISA) aims to observe gravitational waves in the mHz regime over its 10-year mission time. LISA will operate laser interferometers between three spacecrafts. Each spacecraft will utilize independent clocks which determine the sampling times of onboard phasemeters to extract the interferometric phases and, ultimately, gravitational wave signals. To suppress limiting laser frequency noise, signals sampled by each phasemeter need to be combined in post-processing to synthesize virtual equal-arm interferometers. The synthesis in turn requires a synchronization of the independent clocks. This article reports on the experimental verification of a clock synchronization scheme down to LISA performance levels using a hexagonal optical bench. The development of the scheme includes data processing that is expected to be applicable to the real LISA data with minor modifications. Additionally, some noise coupling mechanisms are discussed.

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K. Yamamoto, C. Vorndamme, O. Hartwig, et. al.
Fri, 24 Dec 21
56/58

Comments: 9 pages, 4 figures

Experimental verification of inter-satellite clock synchronization at LISA performance levels [IMA]

http://arxiv.org/abs/2112.12586


The Laser Interferometer Space Antenna (LISA) aims to observe gravitational waves in the mHz regime over its 10-year mission time. LISA will operate laser interferometers between three spacecrafts. Each spacecraft will utilize independent clocks which determine the sampling times of onboard phasemeters to extract the interferometric phases and, ultimately, gravitational wave signals. To suppress limiting laser frequency noise, signals sampled by each phasemeter need to be combined in post-processing to synthesize virtual equal-arm interferometers. The synthesis in turn requires a synchronization of the independent clocks. This article reports on the experimental verification of a clock synchronization scheme down to LISA performance levels using a hexagonal optical bench. The development of the scheme includes data processing that is expected to be applicable to the real LISA data with minor modifications. Additionally, some noise coupling mechanisms are discussed.

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K. Yamamoto, C. Vorndamme, O. Hartwig, et. al.
Fri, 24 Dec 21
30/58

Comments: 9 pages, 4 figures

Interferometric Beam Combination with a Triangular Tricoupler Photonic Chip [IMA]

http://arxiv.org/abs/2112.05017


Beam combiners are important components of an optical/infrared astrophysical interferometer, with many variants as to how to optimally combine two or more beams of light to fringe-track and obtain the complex fringe visibility. One such method is the use of an integrated optics chip that can instantaneously provide the measurement of the visibility without temporal or spatial modulation of the optical path. Current asymmetric planar designs are complex, resulting in a throughput penalty, and so here we present developments into a three dimensional triangular tricoupler that can provide the required interferometric information with a simple design and only three outputs. Such a beam combiner is planned to be integrated into the upcoming $\textit{Pyxis}$ interferometer, where it can serve as a high-throughput beam combiner with a low size footprint. Results into the characterisation of such a coupler are presented, highlighting a throughput of 89$\pm$11% and a flux splitting ratio between 33:33:33 and 52:31:17 over a 20% bandpass. We also show the response of the chip to changes in optical path, obtaining an instantaneous complex visibility and group delay estimate at each input delay.

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J. Hansen, M. Ireland, A. Ross-Adams, et. al.
Fri, 10 Dec 21
69/94

Comments: 15 pages, 8 figures, Submitted to JATIS

Optimal Design of Coatings for Mirrors of Gravitational Wave Detectors: Analytic Turbo Solution via Herpin Equivalent Layers [CL]

http://arxiv.org/abs/2112.04393


In this paper, an analytical solution to the problem of optimal dielectric coating design of mirrors for gravitational wave detectors is found. The technique used to solve this problem is based on Herpin’s equivalent layers, which provide a simple, constructive, and analytical solution. The performance of the Herpin-type design exceeds that of the periodic design and is almost equal to the performance of the numerical, non-constructive optimized design obtained by brute force. Note that the existence of explicit analytic constructive solutions of a constrained optimization problem is not guaranteed in general, when such a solution is found, we speak of turbo optimal solutions.

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V. Pierro, V. Fiumara and F. Chiadini
Thu, 9 Dec 21
3/63

Comments: accepted for publication in “Gravitational Wave Observatory: The Realm of Applied Science” special issue of Applied Science

The spectrally modulated self-coherent camera (SM-SCC): Increasing throughput for focal-plane wavefront sensing [IMA]

http://arxiv.org/abs/2112.04413


The detection and characterization of Earth-like exoplanets is one of the major science drivers for the next generation of telescopes. Current direct imaging instruments are limited by evolving non-common path aberrations (NCPAs). The NCPAs must be compensated for by using the science focal-plane image. A promising sensor is the self-coherent camera (SCC). An SCC modifies the Lyot stop in the coronagraph to introduce a probe electric field. However, the SCC has a weak probe electric field due to the requirements on the pinhole separation. A spectrally modulated self-coherent camera (SM-SCC) is proposed as a solution to the throughput problem. The SM-SCC uses a pinhole with a spectral filter and a dichroic beam splitter, which creates images with and without the probe electric field. This allows the pinhole to be placed closer to the pupil edge and increases the throughput. Combining the SM-SCC with an integral field unit (IFU) can be used to apply more complex modulation patterns to the pinhole and the Lyot stop. A modulation scheme with at least three spectral channels (e.g. IFU) can be used to change the pinhole to an arbitrary aperture with higher throughput. Numerical simulations show that the SM-SCC increases the pinhole throughput by a factor of 32, which increases the wavefront sensor sensitivity by a factor of 5.7. The SM-SCC reaches a contrast of $1\cdot10^{-9}$ for bright targets in closed-loop control with the presence of photon noise, phase errors, and amplitude errors. The contrast floor on fainter targets is photon-noise-limited and reaches $1\cdot10^{-7}$. For bright targets, the SM-SCC-IFU reaches a contrast of $3\cdot10^{-9}$ in closed-loop control with photon noise, amplitude errors, and phase errors. The SM-SCC is a promising focal-plane wavefront sensor for systems that use multiband observations, either through integral field spectroscopy or dual-band imaging.

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S. Haffert
Thu, 9 Dec 21
44/63

Comments: 13 pages, accepted for publication in A&A

Stabilized laser systems at 1550nm wavelength for future gravitational wave detectors [CL]

http://arxiv.org/abs/2112.03792


The continuous improvement of current gravitational wave detectors (GWDs) and the preparations for next generation GWDs place high demands on their stabilized laser sources. Some of the laser souces need to operate at laser wavelengths between 1.5um and 2.2um to support future detectors, based on cooled silicon test masses for thermal noise reduction. We present a detailed characterizations of different commercial low power seed laser sources and power amplifiers at the wavelength of 1550nm with regard to performance parameters needed in GWDs. A combination with the most complete set of actuators was arranged as a master-oscillator power amplifier (MOPA) and integrated into a stabilization environment. We demonstrate the operation of a pre-stabilized laser system (PSL) and characterize its performance. We present the results of this characterization that make this PSL to a highly relevant prototype for future GWDs as well as a low noise light source for other experiments in high precision metrology.

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F. Meylahn and B. Willke
Wed, 8 Dec 21
32/77

Comments: N/A

Arm locking performance with the new LISA design [IMA]

http://arxiv.org/abs/2112.00837


The Laser Interferometer Space Antenna (LISA) is a future space-based gravitational wave (GW) detector designed to be sensitive to sources radiating in the low frequency regime (0.1 mHz to 1 Hz). LISA’s interferometer signals will be dominated by laser frequency noise which has to be suppressed by about 7 orders of magnitude using an algorithm called Time-Delay Interferometry (TDI). Arm locking has been proposed to reduce the laser frequency noise by a few orders of magnitude to reduce the potential risks associated with TDI. In this paper, we present an updated performance model for arm locking for the new LISA mission using 2.5 Gm arm lengths, the currently assumed clock noise, spacecraft motion, and shot noise. We also update the Doppler frequency pulling estimates during lock acquisition.

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S. Ghosh, J. Sanjuan and G. Mueller
Fri, 3 Dec 21
74/81

Comments: 21 pages, 13 figures

Laser guide star return-flux gain from frequency chirping [IMA]

http://arxiv.org/abs/2112.00252


Spectral hole burning reduces sodium laser guide star efficiency. Due to photon recoil, atoms that are initially resonant with the single-frequency laser get Doppler shifted out of resonance, which reduces the return flux. Frequency-chirped (also known as frequency-swept) continuous-wave lasers have the potential to mitigate the effect of spectral hole burning and even increase the laser guide star efficiency beyond the theoretical limit of a single-frequency laser. On-sky measurements of a frequency-chirped, single-frequency laser guide star are performed at the Roque de los Muchachos Observatory on La Palma. In the experiment, a 35-cm telescope and a fast photon counting receiver system are employed to resolve the return flux response during laser frequency sweeps gaining insights into the population dynamics of the sodium layer. At a launched laser power of 16.5 W, we find a maximum gain in return flux of 22\% compared to a fixed-frequency laser. Our results suggest a strong dependence of chirping gain on power density at the mesosphere, i.e. laser power and seeing. Maximum gains are recorded at a chirping amplitude on the order of 150 MHz and a chirping rate of 0.8 MHz $\mu$s$^{-1}$, as predicted by theory. Time-resolved measurements during the chirping period confirm our understanding of the population dynamics in the sodium layer. To our knowledge these are the first measurements of return flux enhancement for laser guide stars excited by a single frequency-chirped continuous-wave laser. For higher laser powers, the effectiveness of chirping is expected to increase, which could be highly beneficial for telescopes equipped with high-power laser guide star adaptive optics systems, also for emerging space awareness applications using laser guide stars such as satellite imaging and ground-to-space optical communications.

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J. Hellemeier, M. Enderlein, M. Hager, et. al.
Thu, 2 Dec 21
21/61

Comments: N/A

Rethinking the modeling of the instrumental response of telescopes with a differentiable optical model [IMA]

http://arxiv.org/abs/2111.12541


We propose a paradigm shift in the data-driven modeling of the instrumental response field of telescopes. By adding a differentiable optical forward model into the modeling framework, we change the data-driven modeling space from the pixels to the wavefront. This allows to transfer a great deal of complexity from the instrumental response into the forward model while being able to adapt to the observations, remaining data-driven. Our framework allows a way forward to building powerful models that are physically motivated, interpretable, and that do not require special calibration data. We show that for a simplified setting of a space telescope, this framework represents a real performance breakthrough compared to existing data-driven approaches with reconstruction errors decreasing 5 fold at observation resolution and more than 10 fold for a 3x super-resolution. We successfully model chromatic variations of the instrument’s response only using noisy broad-band in-focus observations.

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T. Liaudat, J. Starck, M. Kilbinger, et. al.
Thu, 25 Nov 21
24/60

Comments: 10 pages. Accepted for the Fourth Workshop on Machine Learning and the Physical Sciences (NeurIPS 2021)

Rethinking the modeling of the instrumental response of telescopes with a differentiable optical model [IMA]

http://arxiv.org/abs/2111.12541


We propose a paradigm shift in the data-driven modeling of the instrumental response field of telescopes. By adding a differentiable optical forward model into the modeling framework, we change the data-driven modeling space from the pixels to the wavefront. This allows to transfer a great deal of complexity from the instrumental response into the forward model while being able to adapt to the observations, remaining data-driven. Our framework allows a way forward to building powerful models that are physically motivated, interpretable, and that do not require special calibration data. We show that for a simplified setting of a space telescope, this framework represents a real performance breakthrough compared to existing data-driven approaches with reconstruction errors decreasing 5 fold at observation resolution and more than 10 fold for a 3x super-resolution. We successfully model chromatic variations of the instrument’s response only using noisy broad-band in-focus observations.

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T. Liaudat, J. Starck, M. Kilbinger, et. al.
Thu, 25 Nov 21
3/60

Comments: 10 pages. Accepted for the Fourth Workshop on Machine Learning and the Physical Sciences (NeurIPS 2021)

Near ground horizontal high resolution $C_n^2$ profiling from Shack-Hartmann slope and scintillation data [IMA]

http://arxiv.org/abs/2111.08003


CO-SLIDAR is a very promising technique for the metrology of near ground $C_n^2$ profiles. It exploits both phase and scintillation measurements obtained with a dedicated wavefront sensor and allows profiling on the full line of sight between pupil and sources. This technique is applied to an associated instrument based on a mid-IR Shack-Hartmann wavefront sensor, coupled to a 0.35 m telescope, which observes two cooperative sources. This paper presents the first comprehensive description of the CO-SLIDAR method in the context of near ground optical turbulence metrology. It includes the presentation of the physics principles underlying the measurements, of our unsupervised $C_n^2$ profile reconstruction strategy together with the error bar estimation on the reconstructed values. The application to data acquired in a heterogeneous rural landscape during an experimental campaign in Lannemezan (France) demonstrates the ability to obtain profiles with a sampling pitch of about 220 m over a 2.7 km line of sight. The retrieved $C_n^2$ profiles are presented and their variability in space and time is discussed.

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C. Sauvage, C. Robert, L. Mugnier, et. al.
Wed, 17 Nov 21
17/64

Comments: N/A

Optical tweezers in a dusty universe [CL]

http://arxiv.org/abs/2111.06397


Optical tweezers are powerful tools based on focused laser beams. They are able to trap, manipulate and investigate a wide range of microscopic and nanoscopic particles in different media, such as liquids, air, and vacuum. Key applications of this contactless technique have been developed in many fields. Despite this progress, optical trapping applications to planetary exploration is still to be developed. Here we describe how optical tweezers can be used to trap and characterize extraterrestrial particulate matter. In particular, we exploit light scattering theory in the T-matrix formalism to calculate radiation pressure and optical trapping properties of a variety of complex particles of astrophysical interest. Our results open perspectives in the investigation of extraterrestrial particles on our planet, in controlled laboratory experiments, aiming for space tweezers applications: optical tweezers used to trap and characterize dust particles in space or on planetary bodies surface.

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P. Polimeno, A. Magazzu, M. Iati, et. al.
Mon, 15 Nov 21
52/52

Comments: 18 pages, 4 figures, 1 table. Part of EPJ plus Focus Point Issues on “Light Pressure across All Scales”

Study of spectrally resolved thermoluminescence in Tsarev and Chelyabinsk chondrites with a versatile high-sensitive setup [EPA]

http://arxiv.org/abs/2111.01405


Thermoluminescence (TL) research provides a powerful tool for characterizing radiation-induced processes in extraterrestrial matter. One of the challenges in studying the spectral features of the natural TL of stony meteorites is its weak intensity. The present work showcases the capabilities of a high-sensitive original module for measuring the spectrally resolved TL characteristics of the Chelyabinsk and Tsarev chondrites. We have analyzed the emission spectra and glow curves of natural and induced TL over the 300 – 650 nm and RT – 873 K ranges. A quasi-continuous distribution of traps active within the 350 – 650 K range was found in the silicate substructure of both meteorites under study. Based on the general order kinetic formalism and using the natural TL data, we also estimated the activation energies of 0.86 and 1.08 eV for the Chelyabinsk and Tsarev chondrites, respectively.

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A. Vokhmintsev, A. Henaish, T. Sharshar, et. al.
Wed, 3 Nov 21
74/106

Comments: 7 pages, 4 figures, 2 tables, 18 references; Keywords: TL spectroscopy; ordinary chondrite; Chelyabinsk LL5; Tsarev L5; activation energy

Ultralight dark matter searches with KAGRA gravitational wave telescope [CL]

http://arxiv.org/abs/2111.00420


Among various dark matter candidates, bosonic ultralight fields with masses below 1~eV are well motivated. Recently, a number of novel approaches have been put forward to search for ultralight dark matter candidates using laser interferometers at various scales. Those include our proposals to search for axion-like particles (ALPs) and vector fields with laser interferometric gravitational wave detectors. ALPs can be searched for by measuring the oscillating polarization rotation of laser light. Massive vector fields weakly coupled to the standard model sector can also be searched for by measuring the oscillating forces acting on the suspended mirrors of the interferometers. In this paper, the current status of the activities to search for such ultralight dark matter candidates using a gravitational wave detector in Japan, KAGRA, is reviewed. The analysis of data from KAGRA’s observing run in 2020 to search for vector dark matter, and the installation of polarization optics to the arm cavity transmission ports of the interferometer to search for ALPs in future observing runs are underway.

Read this paper on arXiv…

Y. Michimura, T. Fujita, J. Kume, et. al.
Tue, 2 Nov 21
49/93

Comments: 5 pages, 2 figures, Proceedings for the 17th International Conference on Topics in Astroparticle and Underground Physics, Online, August 26 – September 3, 2021

Prototype Schwarzschild-Couder Telescope for the Cherenkov Telescope Array: Commissioning the Optical System [IMA]

http://arxiv.org/abs/2110.07463


A prototype Schwarzschild-Couder Telescope (pSCT) has been constructed at the Fred Lawrence Whipple Observatory as a candidate for the medium-sized telescopes of the Cherenkov Telescope Array Observatory (CTAO). CTAO is currently entering early construction phase of the project and once completed it will vastly improve very high energy gamma-ray detection component in multi-wavelength and multi-messenger observations due to significantly improved sensitivity, angular resolution and field of view comparing to the current generation of the ground-based gamma-ray observatories H.E.S.S., MAGIC and VERITAS. The pSCT uses a dual aspheric mirror design with a $9.7$ m primary mirror and $5.4$ m secondary mirror, both of which are segmented. The Schwarzschild-Couder (SC) optical system (OS) selected for the prototype telescope achieves wide field of view of $8$ degrees and simultaneously reduces the focal plane plate scale allowing an unprecedented compact ($0.78$m diameter) implementation of the high-resolution camera ($6$mm/ $0.067$deg per imaging pixel with $11,328$ pixels) based on the silicon photo-multipliers (SiPMs). The OS of the telescope is designed to eliminate spherical and comatic aberrations and minimize astigmatism to radically improve off-axis imaging and consequently angular resolution across all the field of view with respect to the conventional single-mirror telescopes. Fast and high imaging resolution OS of the pSCT comes with the challenging submillimeter-precision custom alignment system, which was successfully demonstrated with an on-axis point spread function (PSF) of $2.9$ arcmin prior to the first-light detection of the Crab Nebula in 2020. Ongoing and future commissioning activities are reported.

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C. Adams, G. Ambrosi, M. Ambrosio, et. al.
Fri, 15 Oct 21
3/56

Comments: N/A

Model and Measurements of an Optical Stack for Broadband Visible to Near-IR Absorption in TiN KIDs [CL]

http://arxiv.org/abs/2110.05787


Typical materials for optical Kinetic Inductance Detetectors (KIDs) are metals with a natural absorption of 30-50% in the visible and near-infrared. To reach high absorption efficiencies (90-100%) the KID must be embedded in an optical stack. We show an optical stack design for a 60 nm TiN film. The optical stack is modeled as sections of transmission lines, where the parameters for each section are related to the optical properties of each layer. We derive the complex permittivity of the TiN film from a spectral ellipsometry measurement. The designed optical stack is optimised for broadband absorption and consists of, from top (illumination side) to bottom: 85 nm SiOx, 60 nm TiN, 23 nm of SiOx, and a 100 nm thick Al mirror. We show the modeled absorption and reflection of this stack, which has >80% absorption from 400 nm to 1550 nm and near-unity absorption for 500 nm to 800 nm. We measure transmission and reflection of this stack with a commercial spectrophotometer. The results are in good agreement with the model.

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K. Kouwenhoven, I. Elwakil, J. Wingerden, et. al.
Wed, 13 Oct 21
29/80

Comments: 7 pages, 5 figures, submitted to Journal of Low Temperature Physics

Erbium-doped-fiber-based broad visible range frequency comb with a 30 GHz mode spacing for astronomical applications [IMA]

http://arxiv.org/abs/2110.03823


Optical frequency combs have the potential to improve the precision of the radial velocity measurement of celestial bodies, leading to breakthroughs in such fields as exoplanet exploration. For these purposes, the comb must have a broad spectral coverage in the visible wavelength region, a wide mode spacing that can be resolved with a high dispersion spectrograph, and sufficient robustness to operate for long periods even in remote locations. We have realized a comb system with a 30 GHz mode spacing, 62 % available wavelength coverage in the visible region, and 40 dB spectral contrast by combining a robust erbium-doped-fiber-based femtosecond laser, mode filtering with newly designed optical cavities, and broadband-visible-range comb generation using a chirped periodically-poled LiNbO3 ridge waveguide. The system durability and reliability are also promising because of the stable spectrum, which is due to the use of almost all polarization-maintaining fiber optics, moderate optical power, and good frequency repeatability obtained with a wavelength-stabilized laser.

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K. Nakamura, K. Kashiwagi, S. Okubo, et. al.
Mon, 11 Oct 21
53/58

Comments: 19 pages, 5 figures

Piezo-deformable Mirrors for Active Mode Matching in Advanced LIGO [IMA]

http://arxiv.org/abs/2110.00674


The detectors of the laser interferometer gravitational-wave observatory (LIGO) are broadly limited by the quantum noise and rely on the injection of squeezed states of light to achieve their full sensitivity. Squeezing improvement is limited by mode mismatch between the elements of the squeezer and the interferometer. In the current LIGO detectors, there is no way to actively mitigate this mode mismatch. This paper presents a new deformable mirror for wavefront control that meets the active mode matching requirements of advanced LIGO. The active element is a piezo-electric transducer, which actuates on the radius of curvature of a 5 mm thick mirror via an axisymmetric flexure. The operating range of the deformable mirror is 120+-8 mD in vacuum, with an additional 200 mD adjustment range accessible out of vacuum. The scattering into higher-order modes is measured to be <0.2% over the nominal beam radius. These piezo-deformable mirrors meet the stringent noise and vacuum requirements of advanced LIGO and will be used for the next observing run (O4) to control the mode-matching between the squeezer and the interferometer.

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V. Srivastava, G. Mansell, C. Makarem, et. al.
Tue, 5 Oct 21
60/72

Comments: N/A

Arm locking using laser frequency comb [CL]

http://arxiv.org/abs/2109.02642


In this work, we describe an updated version of single arm locking, and the noise amplification due to the nulls can be flexibly restricted with the help of optical frequency comb. We show that, the laser phase noise can be divided by a specific factor with optical frequency comb as the bridge. The analytical results indicate that, the peaks in the science band have been greatly reduced. The performance of the noise suppression shows that the total noise after arm locking can well satisfy the requirement of time delay interferometry, even with the free-running laser source. We also estimate the frequency pulling characteristics of the updated single arm locking, and the results suggest that the pulling rate can be tolerated, without the risk of mode hopping. Arm locking will be a valuable solution for the noise reduction in the space-borne GW detectors. We demonstrate that, with the precise control of the returned laser phase noise, the noise amplification in the science band can be efficiently suppressed based on the updated single arm locking. Not only our method allows the suppression of the peaks, the high gain, low pulling rate, it can also serve for full year, without the potential risk of locking failure due to the arm length mismatch. We finally discuss the unified demonstration of the updated single arm locking, where both the local and the returned laser phase noises can be tuned to generate the expected arm-locking sensor actually. Our work could provide a powerful method for the arm locking in the future space-borne GW detectors.

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H. Wu, J. Ke, P. Wang, et. al.
Wed, 8 Sep 21
58/76

Comments: N/A

Learning the Lantern: Neural network applications to broadband photonic lantern modelling [CL]

http://arxiv.org/abs/2108.13274


Photonic lanterns allow the decomposition of highly multimodal light into a simplified modal basis such as single-moded and/or few-moded. They are increasingly finding uses in astronomy, optics and telecommunications. Calculating propagation through a photonic lantern using traditional algorithms takes $\sim 1$ hour per simulation on a modern CPU. This paper demonstrates that neural networks can bridge the disparate opto-electronic systems, and when trained can achieve a speed-up of over 5 orders of magnitude. We show that this approach can be used to model photonic lanterns with manufacturing defects as well as successfully generalising to polychromatic data. We demonstrate two uses of these neural network models, propagating seeing through the photonic lantern as well as performing global optimisation for purposes such as photonic lantern funnels and photonic lantern nullers.

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D. Sweeney, B. Norris, P. Tuthill, et. al.
Tue, 31 Aug 21
15/73

Comments: 20 pages, 14 figures

Invariants in Polarimetric Interferometry: a non-Abelian Gauge Theory [CL]

http://arxiv.org/abs/2108.11400


The discovery of magnetic fields close to the M87 black hole using Very Long Baseline Interferometry by the Event Horizon Telescope collaboration utilized the novel concept of “closure traces”, that are immune to antenna-based corruptions. We take a fundamentally new approach to this promising tool of polarimetric interferometry. The corruption of measurements of polarized signals at the individual antennas are represented by general $2\times 2$ complex matrices, which are identified with gauge transformations belonging to the group $\textrm{GL}(2,\mathbb{C})$, so the closure traces now appear as gauge-invariant quantities. We apply this formalism to polarimetric interferometry and generalize it to any number of interferometer elements. Our approach goes beyond existing studies in the following respects: (1) we do not need auto-correlations, which are susceptible to large systematic biases, and therefore unreliable (2) we use triangular combinations of correlations as basic building blocks (analogous to the “elementary plaquettes” of lattice gauge theory), and (3) we use the Lorentz group and its properties to transparently identify a complete and independent set of invariants. This set contains all the information immune to corruption available in the interferometer measurements, thus providing robust constraints which would be important in future interferometric studies.

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J. Samuel, R. Nityananda and N. Thyagarajan
Fri, 27 Aug 21
35/67

Comments: 9 pages (including references), 0 figures, submitted to Physical Review Letters. Contains appendices not included in the journal version

Invariants in Co-polar Interferometry: an Abelian Gauge Theory [IMA]

http://arxiv.org/abs/2108.11399


An $N$-element interferometer measures correlations between pairs of array elements. Closure invariants associated with closed loops among array elements are immune to multiplicative, local, element-based corruptions that occur in these measurements. Till now, it has been unclear how a complete set of independent invariants can be analytically determined. We view the local, element-based corruptions in co-polar correlations as gauge tranformations belonging to the gauge group $\textrm{GL}(1,\mathbb{C})$. Closure quantities are then naturally gauge invariant. Using an Abelian $\textrm{GL}(1,\mathbb{C})$ gauge theory, we provide a simple and effective formalism to isolate the complete set of independent closure invariants from co-polar interferometric correlations only using quantities defined on the $(N-1)(N-2)/2$ elementary and independent triangular loops. The $(N-1)(N-2)/2$ closure phases and $N(N-3)/2$ closure amplitudes (totaling $N^2-3N+1$ real invariants), familiar in astronomical interferometry, naturally emerge from this formalism, which unifies what has required separate treatments until now. Our formalism does not require auto-correlations, but can easily include them if reliably measured, including potentially from cross-correlation between two short-spaced elements. The gauge theory framework presented here extends to $\textrm{GL}(2,\mathbb{C}$) for full polarimetric interferometry presented in a companion paper, which generalizes and clarifies earlier work. Our findings can be relevant to cutting-edge co-polar and full polarimetric very long baseline interferometry measurements to determine features very near the event horizons of blackholes at the centers of M87, Centaurus~A, and the Milky Way.

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N. Thyagarajan, R. Nityananda and J. Samuel
Fri, 27 Aug 21
66/67

Comments: 10 pages (including references), 0 figures, submitted to Physical Review D

Experimental investigation of the limitations of polarisation optics for future gravitational wave detectors based on the polarisation Sagnac speedmeter [IMA]

http://arxiv.org/abs/2108.10047


The polarisation Sagnac speedmeter interferometer has the potential to replace the Michelson interferometer as the instrumental basis for future generations of ground-based gravitational wave detectors. The quantum noise benefit of this speedmeter is dependent on high-quality polarisation optics, the polarisation beam-splitter (PBS) and quarter-waveplate (QWP) optics that are key to this detector configuration and careful consideration of the effect of birefringence in the arm cavities of the interferometer. A PBS with an extinction ratio of better than 4000 in transmission and 700 in reflection for a $41^{\circ}$ angle of incidence was characterised along with a QWP of birefringence of $\frac{\lambda}{4} + \frac{\lambda}{324}$. The cavity mirror optics of a 10m prototype polarisation Sagnac speedmeter were measured to have birefringence in the range $1\times10^{-3}$ to $2\times10^{-5}$ radians. This level of birefringence, along with the QWP imperfections, can be canceled out by careful adjustment of the QWP angle, to the extent that the extinction ratio of the PBS is the leading limitation for the polarisation Sagnac speedmeter in terms of polarisation effects.

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A. Spencer, B. Barr, A. Bell, et. al.
Tue, 24 Aug 21
55/76

Comments: N/A

Implementation of a broadband focal plane estimator for high-contrast dark zones [IMA]

http://arxiv.org/abs/2108.08200


The characterization of exoplanet atmospheres using direct imaging spectroscopy requires high-contrast over a wide wavelength range. We study a recently proposed focal plane wavefront estimation algorithm that exclusively uses broadband images to estimate the electric field. This approach therefore reduces the complexity and observational overheads compared to traditional single wavelength approaches. The electric field is estimated as an incoherent sum of monochromatic intensities with the pair-wise probing technique. This paper covers the detailed implementation of the algorithm and an application to the High-contrast Imager for Complex Aperture Telescopes (HiCAT) testbed with the goal to compare the performance between the broadband and traditional narrowband filter approaches.

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S. Redmond, L. Pueyo, L. Pogorelyuk, et. al.
Thu, 19 Aug 21
25/54

Comments: Submitted to OP21O SPIE Optical Engineering + Applications, Techniques and Instrumentation for Detection of Exoplanets X | 11 pages, 7 figures

Dark zone maintenance results for segmented aperture wavefront error drift in a high contrast space coronagraph [IMA]

http://arxiv.org/abs/2108.08216


Due to the limited number of photons, directly imaging planets requires long integration times with a coronagraphic instrument. The wavefront must be stable on the same time scale, which is often difficult in space due to thermal variations and other mechanical instabilities. In this paper, we discuss the implications on future space mission observing conditions of our recent laboratory demonstration of a dark zone maintenance (DZM) algorithm. The experiments are performed on the High-contrast imager for Complex Aperture Telescopes (HiCAT) at the Space Telescope Science Institute (STScI). The testbed contains a segmented aperture, a pair of continuous deformable mirrors (DMs), and a lyot coronagraph. The segmented aperture injects high order wavefront aberration drifts into the system which are then corrected by the DMs downstream via the DZM algorithm. We investigate various drift modes including segmented aperture drift, all three DMs drift simultaneously, and drift correction at multiple wavelengths.

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S. Redmond, L. Pueyo, L. Pogorelyuk, et. al.
Thu, 19 Aug 21
39/54

Comments: Submitted to OP210 SPIE Optical Engineering + Applications, Techniques and Instrumentation for Detection of Exoplanets X | 14 pages, 5 figures

Useful relations for the analysis of stellar scintillation at the entrance pupil of a telescope [IMA]

http://arxiv.org/abs/2108.07319


The development of new techniques for characterizing atmospheric optical turbulence (OT) has become an active topic of research again in recent years. In order to facilitate these studies, we reconsidered known theoretical results and obtained some new practically useful conclusions. We introduce a dimensionless Fresnel filter, which allows us to approximate a polychromatic weighting function (WF) by a monochromatic one with a typical precision of several percent. A so-called dimensionless WF can be easily scaled for a receiving aperture of any size. For the case of a circular aperture and monochromatic radiation, an analytical expression for the WF was found. The WFs for a square aperture and for a circular aperture match with relative difference less than 0.01 if the circular aperture diameter is 1.15 times larger than the square aperture side.
A linear digital filter can be applied to the scintillation signal from an image detector. As an example of digital filtering, we considered the power law filter $\propto f^{5/3}$ with the WF being constant in a wide range of altitudes. We discuss the main limitations of this approach for measuring OT integral: finite pixel size, aliasing, and finite image detector size.

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V. Kornilov, B. Safonov and M. Kornilov
Wed, 18 Aug 21
40/70

Comments: 9 pages, 8 figures, 1 table

Multipole representation of a generic gravitational lens [CL]

http://arxiv.org/abs/2108.07172


We consider gravitational lensing by a generic extended mass distribution. We represent the static external gravitational field of the lens as a potential via an infinite set of symmetric trace free (STF) moments. We discuss the possibility of determining the physical characteristics of the lens including its shape, orientation and composition via gravitational lensing. To do that, we consider STF multipole moments for several well-known solids with uniform density. We discuss the caustics formed by the point spread function (PSF) of such lenses, and also the view seen by an imaging telescope placed in the strong interference region of the lens. We show that at each STF order, all the bodies produce similar caustics that are different only by their magnitudes and orientations. Furthermore, there is ambiguity in determining the shape of the lens and its mass distribution if only a limited number of moments are used in the model. This result justifies the development of more comprehensive lens models that contain a greater number of multipole moments. At the same time, inclusion of higher multipole moments leads to somewhat limited improvements as their contributions are suppressed by corresponding powers of the small parameter $(R/b)^\ell$, where $R$ characterizes the body’s physical size and $b$ is the impact parameter, resulting in a weaker signature from those multipole moments in the PSF. Thus, in realistic observations there will always be some ambiguity in the optical properties of a generic lens, unless the properties of the lens can be determined independently, as in the case of the solar gravitational lens (SGL). Our results are novel and offer new insight into gravitational lensing by realistic astrophysical systems.

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S. Turyshev and V. Toth
Tue, 17 Aug 21
26/56

Comments: 20 pages, 7 figures

Colour remote sensing of the impact of artificial light at night (II): Calibration of DSLR-based images from the International Space Station [IMA]

http://arxiv.org/abs/2108.07050


Nighttime images taken with DSLR cameras from the International Space Station (ISS) can provide valuable information on the spatial and temporal variation of artificial nighttime lighting on Earth. In particular, this is the only source of historical and current visible multispectral data across the world (DMSP/OLS and SNPP/VIIRS-DNB data are panchromatic and multispectral in the infrared but not at visible wavelengths). The ISS images require substantial processing and proper calibration to exploit intensities and ratios from the RGB channels. Here we describe the different calibration steps, addressing in turn Decodification, Linearity correction (ISO dependent), Flat field/Vignetting, Spectral characterization of the channels, Astrometric calibration/georeferencing, Photometric calibration (stars)/Radiometric correction (settings correction – by exposure time, ISO, lens transmittance, etc) and Transmittance correction (window transmittance, atmospheric correction). We provide an example of the application of this processing method to an image of Spain.

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A. Miguel, J. Zamorano, M. Aubé, et. al.
Tue, 17 Aug 21
47/56

Comments: N/A

Light-Sail Photonic Design for Fast-Transit Earth Orbital Maneuvering and Interplanetary Flight [CL]

http://arxiv.org/abs/2107.09121


Space exploration is of paramount importance to advancing fundamental science and providing global services, such as navigation and communications. However, today’s space missions are hindered by limitations of existing propulsion technologies. Here, we examine the use of laser-driven light-sailing for agile Earth orbital maneuvering and for fast-transit exploration of the solar system and interstellar medium. We show that laser propulsion becomes practical at laser powers around 100 kW and laser array sizes ~1 m, which are feasible in the near term. Our analysis indicates that lightweight (1 g – 100 g) wafer-scale (~10 cm) spacecraft may be propelled by lasers to orbits that are beyond the reach of current systems. We further compare our findings with previous interstellar laser propulsion studies, and show that our approach is less constricting on laser architecture and spacecraft photonic design. We discuss material requirements and photonic designs. We show that light-sails made of silicon nitride and boron nitride are particularly well suited for discussed applications. Our architecture may pave the way to ubiquitous Earth orbital networks and fast-transit low-cost missions across the solar system.

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H. Tung and A. Davoyan
Wed, 21 Jul 21
67/83

Comments: N/A

A Novel Microstructure-Based Model to Explain the IceCube Ice Anisotropy [HEAP]

http://arxiv.org/abs/2107.08692


The IceCube Neutrino Observatory instruments about 1 km$^3$ of deep, glacial ice at the geographic South Pole using 5160 photomultipliers to detect Cherenkov light of charged relativistic particles. Most of IceCube’s science goals rely heavily on an ever more precise understanding of the optical properties of the instrumented ice. A curious light propagation effect observed by the experiment is an anisotropic attenuation, which is aligned with the local flow of the ice. Having recently identified curved photon trajectories resulting from asymmetric light diffusion in the birefringent polycrystalline microstructure of the ice as the most likely underlying cause of this effect, work is now ongoing to optimize the model parameters (effectively deducing the average crystal size and shape in the detector). We present the parametrization of the birefringence effect in our photon propagation simulation, the fitting procedures and results as well as the impact of the new ice model on data-MC agreement.

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M. Rongen and D. Chirkin
Tue, 20 Jul 21
37/104

Comments: Presented at the 37th International Cosmic Ray Conference (ICRC 2021). See arXiv:2107.06966 for all IceCube contributions

Design, simulation and characterization of integrated photonic spectrographs for Astronomy I: Generation-I AWG devices based on canonical layouts [IMA]

http://arxiv.org/abs/2107.06342


We present an experimental study on our first generation of custom-developed arrayed waveguide gratings (AWG) on silica platform for spectroscopic applications in near-infrared astronomy. We provide a comprehensive description of the design, numerical simulation and characterization of several AWG devices aimed at spectral resolving powers of 15,000 – 60,000 in the astronomical H-band. We evaluate the spectral characteristics of the fabricated devices in terms of insertion loss and estimated spectral resolving power and compare the results with numerical simulations. We estimate resolving powers of up to 18,900 from the output channel 3-dB transmission bandwidth. Based on the first characterization results, we select two candidate AWGs for further processing by removal of the output waveguide array and polishing the output facet to optical quality with the goal of integration as the primary diffractive element in a cross-dispersed spectrograph. We further study the imaging properties of the processed AWGs with regards to spectral resolution in direct imaging mode, geometry-related defocus aberration, and polarization sensitivity of the spectral image. We identify phase error control, birefringence control, and aberration suppression as the three key areas of future research and development in the field of high-resolution AWG-based spectroscopy in astronomy.

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A. Stoll, K. Madhav and M. Roth
Thu, 15 Jul 21
38/63

Comments: 25 pages, 25 figures, 3 tables. (c) 2021 Optical Society of America. Users may use, reuse, and build upon the article, or use the article for text or data mining, so long as such uses are for non-commercial purposes and appropriate attribution is maintained. All other rights are reserved

Demonstration of high-efficiency photonic lantern couplers for PolyOculus [IMA]

http://arxiv.org/abs/2107.05721


The PolyOculus technology produces large-area-equivalent telescopes by using fiber optics to link modules of multiple semi-autonomous, small, inexpensive, commercial-off-the-shelf telescopes. Crucially, this scalable design has construction costs which are > 10x lower than equivalent traditional large-area telescopes. We have developed a novel photonic lantern approach for the PolyOculus fiber optic linkages which potentially offers substantial advantages over previously considered free-space optical linkages, including much higher coupling efficiencies. We have carried out the first laboratory tests of a photonic lantern prototype developed for PolyOculus, and demonstrate broadband efficiencies of ~91%, confirming the outstanding performance of this technology.

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C. Moraitis, J. Alvarado-Zacarias, R. Amezcua-Correa, et. al.
Wed, 14 Jul 21
45/67

Comments: 13 pages, 8 figures

The Simons Observatory: HoloSim-ML: machine learning applied to the efficient analysis of radio holography measurements of complex optical systems [IMA]

http://arxiv.org/abs/2107.04138


Near-field radio holography is a common method for measuring and aligning mirror surfaces for millimeter and sub-millimeter telescopes. In instruments with more than a single mirror, degeneracies arise in the holography measurement, requiring multiple measurements and new fitting methods. We present HoloSim-ML, a Python code for beam simulation and analysis of radio holography data from complex optical systems. This code uses machine learning to efficiently determine the position of hundreds of mirror adjusters on multiple mirrors with few micron accuracy. We apply this approach to the example of the Simons Observatory 6m telescope.

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G. Chesmore, A. Adler, N. Cothard, et. al.
Mon, 12 Jul 21
30/49

Comments: Software is publicly available at: this https URL

Fibre Fabry-Pérot Astrophotonic Correlation Spectroscopy for Remote Gas Identification and Radial Velocity Measurements [IMA]

http://arxiv.org/abs/2107.04494


We present a novel remote gas detection and identification technique based on correlation spectroscopy with a piezoelectric tunable fibre-optic Fabry-P\’erot filter. We show that the spectral correlation amplitude between the filter transmission window and gas absorption features is related to the gas absorption optical depth, and that different gases can be distinguished from one another using their correlation signal phase. Using an observed telluric-corrected, high-resolution near-infrared spectrum of Venus, we show via simulation that the Doppler shift of gases lines can be extracted from the phase of the lock-in signal using low-cost, compact, and lightweight fibre-optic components with lock-in amplification to improve the signal-to-noise ratio. This correlation spectroscopy technique has applications in the detection and radial velocity determination of faint spectral features in astronomy and remote sensing. We experimentally demonstrate remote CO2 detection system using a lock-in amplifier, fibre-optic Fabry-P\’erot filter, and single channel photodiode.

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R. Cheriton, A. Densmore, S. Sivanandam, et. al.
Mon, 12 Jul 21
49/49

Comments: N/A

Twisted light, a new tool for General Relativity and beyond [CL]

http://arxiv.org/abs/2107.01599


We describe and present the first observational evidence that light propagating near a rotating black hole is twisted in phase and carries orbital angular momentum. The novel use of this physical observable as an additional tool for the previously known techniques of gravitational lensing allows us to directly measure, for the first time, the spin parameter of a black hole. With the additional information encoded in the orbital angular momentum, not only can we reveal the actual rotation of the compact object, but we can also use rotating black holes as probes to test General Relativity.

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F. Tamburini, F. Feleppa and B. Thidé
Tue, 6 Jul 21
36/74

Comments: This essay received an Honorable Mention in the 2021 Essay Competition of the Gravity Research Foundation

Seeking celestial Positronium with an OH-suppressed diffraction-limited spectrograph [IMA]

http://arxiv.org/abs/2106.09921


Celestially, Positronium (Ps), has only been observed through gamma-ray emission produced by its annihilation. However, in its triplet state, a Ps atom has a mean lifetime long enough for electronic transitions to occur between quantum states. This produces a recombination spectrum observable in principle at near IR wavelengths, where angular resolution greatly exceeding that of the gamma-ray observations is possible. However, the background in the NIR is dominated by extremely bright atmospheric hydroxyl (OH) emission lines. In this paper we present the design of a diffraction-limited spectroscopic system using novel photonic components – a photonic lantern, OH Fiber Bragg Grating filters, and a photonic TIGER 2-dimensional pseudo-slit – to observe the Ps Balmer alpha line at 1.3122 microns for the first time.

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J. Robertson, S. Ellis, Q. Yu, et. al.
Mon, 21 Jun 21
41/54

Comments: 6 pages, 9 Figures, 2 Tables. Accepted to Applied Optics feature issue on Astrophotonics

An Open-Source Gaussian Beamlet Decomposition Tool for Modeling Astronomical Telescopes [IMA]

http://arxiv.org/abs/2106.09162


In the pursuit of directly imaging exoplanets, the high-contrast imaging community has developed a multitude of tools to simulate the performance of coronagraphs on segmented-aperture telescopes. As the scale of the telescope increases and science cases move toward shorter wavelengths, the required physical optics propagation to optimize high-contrast imaging instruments becomes computationally prohibitive. Gaussian Beamlet Decomposition (GBD) is an alternative method of physical optics propagation that decomposes an arbitrary wavefront into paraxial rays. These rays can be propagated expeditiously using ABCD matrices, and converted into their corresponding Gaussian beamlets to accurately model physical optics phenomena without the need of diffraction integrals. The GBD technique has seen recent development and implementation in commercial software (e.g. FRED, CODE V, ASAP) but appears to lack an open-source platform. We present a new GBD tool developed in Python to model physical optics phenomena, with the goal of alleviating the computational burden for modeling complex apertures, many-element systems, and introducing the capacity to model misalignment errors. This study demonstrates the synergy of the geometrical and physical regimes of optics utilized by the GBD technique, and is motivated by the need for advancing open-source physical optics propagators for segmented-aperture telescope coronagraph design and analysis. This work illustrates GBD with Poisson’s spot calculations and show significant runtime advantage of GBD over Fresnel propagators for many-element systems.

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J. Ashcraft and E. Douglas
Fri, 18 Jun 21
49/62

Comments: 13 pages, 9 figures, submitted to SPIE Astronomical Telescopes & Instrumentation 2020

Good luck lies in odd numbers: axion dark matter search using arm cavity transmitted beams of gravitational wave detectors [CL]

http://arxiv.org/abs/2106.06800


Axion is a promising candidate for ultralight dark matter which may cause a polarization rotation of laser light. Recently, a new idea of probing the axion dark matter by optical linear cavities used in the arms of gravitational wave detectors has been proposed [Phys. Rev. Lett. 123, 111301 (2019)]. In this article, a realistic scheme of the axion dark matter search with the arm cavity transmission ports is revisited. Since photons detected by the transmission ports travel in the cavity for odd-number of times, the effect of axion dark matter on their phases is not cancelled out and the sensitivity at low-mass range is significantly improved compared to the search using reflection ports. We also take into account the stochastic nature of the axion field and the availability of the two detection ports in the gravitational wave detectors. The sensitivity to the axion-photon coupling, $g_{a\gamma}$, of the ground-based gravitational wave detector, such as Advanced LIGO, with 1-year observation is estimated to be $g_{a\gamma} \sim 3\times10^{-12}$ GeV$^{-1}$ below the axion mass of $10^{-15}$ eV, which improves upon the limit achieved by the CERN Axion Solar Telescope.

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K. Nagano, H. Nakatsuka, S. Morisaki, et. al.
Tue, 15 Jun 21
47/67

Comments: 9 pages, 4 figures

Potential of commercial SiN MPW platforms for developing mid/high-resolution integrated photonic spectrographs for astronomy [IMA]

http://arxiv.org/abs/2106.04598


Integrated photonic spectrographs offer an avenue to extreme miniaturization of astronomical instruments, which would greatly benefit extremely large telescopes and future space missions. These devices first require optimization for astronomical applications, which includes design, fabrication and field-testing. Given the high costs of photonic fabrication, Multi-Project Wafer (MPW) SiN offerings, where a user purchases a portion of a wafer, provide a convenient and affordable avenue to develop this technology. In this work we study the potential of two commonly used SiN waveguide geometries by MPW foundries, i.e. square and rectangular profiles to determine how they affect the performance of mid-high resolution arrayed waveguide grating spectrometers around 1.5 $\mu$m. Specifically, we present results from detailed simulations on the mode sizes, shapes, and polarization properties, and on the impact of phase errors on the throughput and cross talk as well as some laboratory results of coupling and propagation losses. From the MPW-run tolerances and our phase-error study, we estimate that an AWG with R $\sim$ 10,000 can be developed with the MPW runs and even greater resolving power is achievable with more reliable, dedicated fabrication runs. Depending on the fabrication and design optimizations, it is possible to achieve throughputs $\sim 60\%$ using the SiN platform. Thus, we show that SiN MPW offerings are highly promising and will play a key role in integrated photonic spectrograph developments for astronomy.

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P. Gatkine, N. Jovanovic, C. Hopgood, et. al.
Thu, 10 Jun 21
42/77

Comments: Accepted at Applied Optics, Special Issue on Astrophotonics (24 pages, 13 figures, 3 tables)

Gravitational analogue of Faraday rotation in the magnetized Kerr and Reissner-Nordström spacetimes [CL]

http://arxiv.org/abs/2106.03520


It is known that the gravitational analogue of the Faraday rotation arises in the rotating spacetime due to the non-zero gravitomagnetic field. In this paper, we show that it also arises in the `non-rotating’ Reissner-Nordstr\”om spacetime, if it is immersed in a uniform magnetic field. The non-zero angular momentum (due to the presence of electric charge and magnetic field) of the electromagnetic field acts as the twist potential to raise the gravitational Faraday rotation in the said spacetime. The twisting can still exist even if the mass of the spacetime vanishes. In other words, the massless charged particle(s) immersed in a uniform magnetic field, able to twist the spacetime in principle, and responsible for the rotation of the plane of polarization of light. This, in fact, could have some applications in the basic physics and the analogue models of gravity. Here, we also study the effect of magnetic fields in the Kerr and Reissner-Nordstr\”om spacetimes, and derive the exact expressions for the gravitational Faraday rotation in the magnetized Kerr and Reissner-Nordstr\”om spacetimes. Considering the correction due to the magnetic field in the lowest possible order, we show that the logarithm correction of the distance of the source and observer in the gravitational Faraday rotation for the said spacetimes is an important consequence of the presence of magnetic field. From the astrophysical point of view, our result could be helpful to study the effects of (gravito-)magnetic fields on the propagation of polarized photons in the strong gravity regime of the rapidly rotating collapsed object.

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C. Chakraborty
Tue, 8 Jun 21
49/86

Comments: 15 pages, no figures

Thermo-accelerative optimization of relativistic lightsails [IMA]

http://arxiv.org/abs/2106.03558


The Breakthrough Starshot Initiative aims to send a gram-scale probe to Proxima Centuri B using a high-power laser-accelerated lightsail traveling at relativistic speeds. Thermal degradation is a key consideration in the design of lightsails because the intense laser power required will heat sails to extreme temperatures. Previous work has evaluated lightsails primarily based on their acceleration distance, with thermal considerations being a secondary concern. In this work, we demonstrate co-optimization of accelerative and thermal performance for sail designs that use a multilayer connected photonic crystal composed of layered 2H-phase Molybdenum Disulfide and crystalline Silicon Nitride. We highlight the inverse relationship between thermal band extinction coefficient and lightsail maximum steady state temperature, then characterize the trade-off between acceleration distance and maximum sail temperature. Additionally, we introduce thermally endurable acceleration minimum (TEAM) as a summary result that characterizes the best realistic acceleration distance achievable within a sail design space, and report a TEAM value of 16.2 Gm for our class of designs. We conclude by demonstrating a multiscale Mie resonance-based approach to enhancing sail emissivity over infrared wavelengths that simultaneously preserves favorable lightsail acceleration distance characteristics.

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J. Brewer, M. Campbell, P. Kumar, et. al.
Tue, 8 Jun 21
63/86

Comments: 14 pages, 4 figures

Variation on a Zernike wavefront sensor theme: optimal use of photons [IMA]

http://arxiv.org/abs/2105.07690


The Zernike wavefront sensor (ZWFS) is a concept belonging to the wide class Fourier-filtering wavefront sensor (FFWFS). The ZWFS is known for its extremely high sensitivity while having a low dynamic range, which makes it a unique sensor for second stage adaptive optics (AO) systems or quasi-static aberrations calibration sensor. This sensor is composed of a focal plane mask made of a phase shifting dot fully described by two parameters: its diameter and depth. In this letter, we aim to improve the performance of this sensor by changing the diameter of its phase shifting dot. We begin with a general theoretical framework providing an analytical description of the FFWFS properties, then we predict the expected ZWFS sensitivity for different configurations of dot diameters and depths. The analytical predictions are then validated with end-to-end simulations. From this, we propose a variation of the classical ZWFS shape which exhibits extremely appealing properties. We show that the ZWFS sensitivity can be optimized by modifying the dot diameter and even reach the optimal theoretical limit, with a trade-off for low spatial frequencies sensitivity. As an example, we show that a ZWFS with a 2{\lambda}/D dot diameter (where {\lambda} is the sensing wavelength and D the telescope diameter), hereafter called Z2WFS, exhibits a sensitivity twice higher than the classical 1.06{\lambda}/D ZWFS for all the phase spatial components except for tip-tilt modes. Furthermore, this gain in sensitivity does not impact the dynamic range of the sensor, and the Z2WFS exhibits a similar dynamical range as the classical 1.06{\lambda}/D ZWFS. This study opens the path to the conception of diameter-optimized ZWFS.

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V. Chambouleyron, O. Fauvarque, J. Sauvage, et. al.
Tue, 18 May 21
54/77

Comments: N/A