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.
M. Kreider, C. Fredrick, R. Terrien, et. al.
Fri, 21 Oct 22
4/76
Comments: 13 pages, 8 figures
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