24 July 2014 Current progress of optical alignment procedure of CLASP's Lyman-alpha polarimetry instrument
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Abstract
The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) is a sounding-rocket instrument currently under development at the National Astronomical Observatory of Japan (NAOJ) as a part of an international collaboration. CLASP’s optics are composed of a Cassegrain telescope and a spectro-polarimeter which are designed to achieve an unprecedentedly accurate polarization measurement of the Ly-α line at 121.6nm emitted from the solar upper-chromosphere and transition region. CLASP’s first flight is scheduled for August 2015. Reaching such accuracy requires a careful alignment of the optical elements to optimize the image quality at 121.6 nm. However Ly-α is absorbed by air and therefore the optics alignment has to be done under vacuum condition which makes any experiment difficult. To bypass this issue, we proposed to align the telescope and the spectrograph separately in visible light. Hence we present our alignment procedure for both telescope and spectro-polarimeter. We will explain details about the telescope preliminary alignment before mirrors coating, which was done in April 2014, present the telescope combined optical performance and compare them to CLASP tolerance. Then we will present details about an experiment designed to confirm our alignment procedure for the CLASP spectro-polarimeter. We will discuss the resulting image quality achieved during this experiment and the lessons learned.
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G. Giono, R. Ishikawa, Y. Katsukawa, T. Bando, R. Kano, Y. Suematsu, N. Narukage, Taro Sakao, K. Kobayashi, F. Auchère, "Current progress of optical alignment procedure of CLASP's Lyman-alpha polarimetry instrument", Proc. SPIE 9144, Space Telescopes and Instrumentation 2014: Ultraviolet to Gamma Ray, 91443E (24 July 2014); doi: 10.1117/12.2055704; https://doi.org/10.1117/12.2055704
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