Polishing test of a poly-crystal calcium fluoride lens: toward the development of TMT WFOS

Shinobu Ozaki; Satoshi Miyazaki; Toshihiro Tsuzuki; Yoko Tanaka

doi:10.1117/12.2232226

9 August 2016 Polishing test of a poly-crystal calcium fluoride lens: toward the development of TMT WFOS

Shinobu Ozaki, Satoshi Miyazaki, Toshihiro Tsuzuki, Yoko Tanaka

Proceedings Volume 9908, Ground-based and Airborne Instrumentation for Astronomy VI; 99089N (2016) https://doi.org/10.1117/12.2232226
Event: SPIE Astronomical Telescopes + Instrumentation, 2016, Edinburgh, United Kingdom

Abstract

Wide-Field Optical Spectrograph (WFOS) is one of the first-light instruments of Thirty Meter Telescope (TMT), and developed in an international collaboration led by University of California Santa Cruz. It covers the wavelength range from 310 nm to 1 μm which is divided at around 550 nm by a dichroic mirror. Calcium Fluoride (CaF2) is very useful to reduce aberration and has good transmittance even at 310 nm. Because a large mono-crystal CaF2 is difficult to be manufactured, we might have to use a poly-crystal CaF2. Comparing a mono-crystal, the poly-crystal is expected to have worse optical index homogeneity and larger surface figure error after polishing. Those effects on an image quality are unclear. To verify those effects, we conducted a polishing test of a small poly-crystal CaF2 lens as a first step. As a result, we found figure error around the boundary. The figure error is ~139 nm PV and ~26 nm RMS. Comparing a Zemax simulation, it is confirmed that the figure error does not have significant effect on the image quality.

Citation Download Citation

Shinobu Ozaki, Satoshi Miyazaki, Toshihiro Tsuzuki, and Yoko Tanaka "Polishing test of a poly-crystal calcium fluoride lens: toward the development of TMT WFOS", Proc. SPIE 9908, Ground-based and Airborne Instrumentation for Astronomy VI, 99089N (9 August 2016); https://doi.org/10.1117/12.2232226

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