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Analysis of the optical design for the SAFIR telelscope

Goldsmith, Paul and Khayatian, Behrouz and Bradford, Matt and Dragovan, Mark and Hoppe, Daniel and Imbriale, William and Lee, Roger and Paine, Chris and Turner, Philip and Yorke, Harold and Zmuidzinas, Jonas (2006) Analysis of the optical design for the SAFIR telelscope. In: Space Telescopes and Instrumentation I: Optical, Infrared, and Millimeter. Proceedings of SPIE. No.6265. Society of Photo-Optical Instrumentation Engineers (SPIE) , Bellingham, WA, Art. No. 62654A.

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SAFIR, the Single Aperture Far Infra Red Observatory, is a very powerful space mission that will achieve background-limited sensitivity in the far infrared-submillimeter spectral region. Many processes of enormous interest to astronomers can best be studied in this wavelength range, but require the demanding combination of high sensitivity, good angular resolution, and spectroscopic capability. SAFIR is a 10m class telescope offering good angular resolution, cooled to below 5 K in order to achieve background-limited sensitivity, and equipped with a complement of large-format cameras and broadband spectrometers. Successful operation of such a facility is critically dependent on achieving the level of sensitivity expected, but this is rendered difficult by potential pickup from unwanted sources of radiation. This problem is exacerbated by the fact that the emission from the optical system itself is minimal due to its low temperature, thus emphasizing the importance of minimizing pickup from unwanted astronomical sources of radiation, including the emission from dust in our solar system (analogous to the zodiacal light, hence "zodi"), and the emission from warm dust in the Milky Way (Galactic "cirrus"). The extreme sensitivity of SAFIR to these unwanted sources of radiation makes it essential to understand the relative sensitivity of the telescope/detector system to radiation coming from angles far outside the main beam, and to develop designs which minimize this pickup. In this paper we analyze in some detail the relative telescope sensitivity (referred to as the antenna pattern by microwave engineers) for different designs of SAFIR. These calculations include edge diffraction from the secondary and primary reflector, and also the effect of blockage by the secondary and blockage and scattering by support legs in a symmetric system. By convolving the antenna pattern with the brightness of the sky due to the zodi and cirrus, we can calculate the power received when the antenna is pointed in any specified direction. We can also compare the undesired pickup for different designs, in particular symmetric vs. asymmetric (off-axis or unblocked) antenna configurations. These considerations are vital for achieving the most efficient SAFIR design possible, in terms of achieving maximum sensitivity while being able to observe over a large fraction of the sky.

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Goldsmith, Paul0000-0002-6622-8396
Imbriale, William0000-0002-5992-8749
Additional Information:© 2006 Society of Photo-Optical Instrumentation Engineers (SPIE). This research described in this paper has been carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. We thank André Girerd for his input to the project and suggestions that improved this paper.
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Series Name:Proceedings of SPIE
Issue or Number:6265
Record Number:CaltechAUTHORS:20190517-150918469
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Official Citation:Paul Goldsmith, Behrouz Khayatian, Matt Bradford, Mark Dragovan, Daniel Hoppe, William Imbriale, Roger Lee, Chris Paine, Philip Turner, Harold Yorke, and Jonas Zmuidzinas "Analysis of the optical design for the SAFIR telelscope", Proc. SPIE 6265, Space Telescopes and Instrumentation I: Optical, Infrared, and Millimeter, 62654A (16 June 2006); doi: 10.1117/12.670051;
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:95576
Deposited By: Tony Diaz
Deposited On:20 May 2019 16:33
Last Modified:07 Dec 2020 23:32

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