The real throughput: Site plus optics plus in-situ cleaning for an optical-IR telescope

Saeko S. Hayashi; Hirofumi Okita; Eric Hansen; Angel Otarola; Takuya Yamashita; Shin Oya; Tomonori Usuda

doi:10.1117/12.2557897

13 December 2020 The real throughput: Site plus optics plus in-situ cleaning for an optical-IR telescope

Saeko S. Hayashi, Hirofumi Okita, Eric Hansen, Angel Otarola, Takuya Yamashita, Shin Oya, Tomonori Usuda

Proceedings Volume 11445, Ground-based and Airborne Telescopes VIII; 114456P (2020) https://doi.org/10.1117/12.2557897
Event: SPIE Astronomical Telescopes + Instrumentation, 2020, Online Only

Conference Poster

Abstract

How much light from the astronomical object actually reaches the focal plane of a telescope? To what extent the sensitivity can be extended to both ends of the visible wavelengths – ultraviolet (UV) and infrared (IR) – as much as possible from the ground? And how to maintain good throughput of the telescope optics? In this report, we make a simplified model to show effect in the reflectivity change of the telescope mirror from the recoating and cleaning versus degradation focusing on a segmented primary mirror of a telescope. The better understandings and monitoring of these competing factors will help fine tune the scheduling of the in-situ cleaning such as CO₂ cleaning. By maintaining the high throughput of the optics, it becomes more feasible to catch rare atmospheric condition whenever it becomes available for very sensitive UV or IR observations during Moon’s dark and bright phases, respectively. The degradation not recoverable by the cleaning is reset by replacing dirty segments with freshly coated ones. The importance of regular in-situ cleaning is evident when it takes long time to replace the large number of freshly coated segments. It is important to clean the entire aperture as much as possible when a wet condition is forecast; for once the contamination settles on the surface, CO₂ cleaning alone won’t be able to recover good surface characteristics of reflectivity, scattering, and emissivity.

Conference Presentation

Citation Download Citation

Saeko S. Hayashi, Hirofumi Okita, Eric Hansen, Angel Otarola, Takuya Yamashita, Shin Oya, and Tomonori Usuda "The real throughput: Site plus optics plus in-situ cleaning for an optical-IR telescope", Proc. SPIE 11445, Ground-based and Airborne Telescopes VIII, 114456P (13 December 2020); https://doi.org/10.1117/12.2557897

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