http://arxiv.org/abs/1402.4091
Precision measurements of the Sunyaev-Zel’dovich Effect (SZE) in clusters of galaxies require excellent rejection of common-mode signals and wide frequency coverage. We describe an imaging, lossless, differential Fourier Transform Spectrometer (FTS), optimized for measurements of faint brightness gradients at millimeter wavelengths. Our instrument is based on a Martin-Puplett Interferometer (MPI) configuration. We combine two MPIs working synchronously, in order to use the whole input power. In our implementation the observed sky field is divided in two halves along the meridian, and each half field corresponds to one of the two input ports of the MPI. In this way each detector in the FTS focal planes measures the difference in brightness between two sky pixels, symmetrically located with respect to the meridian. Exploiting the high common-mode rejection of the MPI we can measure small sky brightness gradients over a large isotropic background. The instrument works in the range $\sim$ 1$\div$20 cm$^{-1}$ (30$\div$600 GHz), has a maximum spectral resolution $1/(2 \ OPD) = 0.063 \ cm^{-1}$ (1.9 GHz), and an unvignetted throughput of 2.3 cm$^2$sr. It occupies a volume of 0.7$\times$0.7$\times$0.33 m$^3$ and has a weight of 70 kg. This design can be implemented as a cryogenic unit to be used in space, as well as a room-temperature unit working at the focus of sub-orbital and ground based mm-wave telescopes. The first in-flight test of the instrument is with the OLIMPO experiment on a stratospheric balloon; a larger implementation is being prepared for the Sardinia Radio Telescope.
A. Schillaci, G. Alessandro, P. Bernardis, et. al.
Tue, 18 Feb 14
55/72
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