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Wavefront error measurements and alignment of CLASP2 telescope with a dual-band pass cold mirror coated primary mirror
Author(s): Masaki Yoshida; Donguk Song; Ryoko Ishikawa; Ryouhei Kano; Yukio Katsukawa; Yoshinori Suematsu; Noriyuki Narukage; Masahito Kubo; Kazuya Shinoda; Takenori J. Okamoto; David E. McKenzie; Laurel A. Rachmeler; Frédéric Auchère; Javier Trujillo Bueno
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Paper Abstract

“Chromospheric LAyer Spectro-Polarimeter (CLASP2)” is the next sounding rocket experiment of the “Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP)” that succeeded in observing for the first time the linear polarization spectra in the hydrogen Lyman-α line (121.6 nm) and is scheduled to be launched in 2019. In CLASP2, we will carry out full Stokes-vector spectropolarimetric observations in the Mg ii h and k lines near 280 nm with the spectro-polarimeter (SP), while imaging observations in the Lyman-α line will be conducted with the slitjaw optics (SJ). For the wavelength selection of CLASP2, the primary mirror of the telescope uses a new dual-band pass cold mirror coating targeting both at 121.6 nm and 280 nm. Therefore, we have to perform again the alignment of the telescope after the installation of the recoated primary mirror. Before unmounting the primary mirror from the telescope structure, we measured the wave-front error (WFE) of the telescope. The measured WFE map was consistent with what we had before the CLASP flight, clearly indicating that the telescope alignment has been maintained even after the flight. After the re-coated primary mirror was installed the WFE was measured, and coma aberration was found to be larger. Finally, the secondary mirror shim adjustments were carried out based on the WFE measurements. In CLASP2 telescope, we improved a fitting method of WFE map (applying 8th terms circular Zernike polynomial fitting instead of 37th terms circular Zernike fitting) and the improved method enables to achieve better performance than CLASP telescope. Indeed, WFE map obtained after the final shim adjustment indicated that the required specification (< 5.5 μm RMS spot radius) that is more stringent than CLASP telescope was met.

Paper Details

Date Published: 6 July 2018
PDF: 13 pages
Proc. SPIE 10699, Space Telescopes and Instrumentation 2018: Ultraviolet to Gamma Ray, 1069930 (6 July 2018); doi: 10.1117/12.2312463
Show Author Affiliations
Masaki Yoshida, Graduate Univ. for Advanced Studies (Japan)
National Astronomical Observatory of Japan (Japan)
Donguk Song, National Astronomical Observatory of Japan (Japan)
Ryoko Ishikawa, National Astronomical Observatory of Japan (Japan)
Ryouhei Kano, National Astronomical Observatory of Japan (Japan)
Yukio Katsukawa, National Astronomical Observatory of Japan (Japan)
Yoshinori Suematsu, National Astronomical Observatory of Japan (Japan)
Noriyuki Narukage, National Astronomical Observatory of Japan (Japan)
Masahito Kubo, National Astronomical Observatory of Japan (Japan)
Kazuya Shinoda, National Astronomical Observatory of Japan (Japan)
Takenori J. Okamoto, National Astronomical Observatory of Japan (Japan)
David E. McKenzie, NASA Marshall Space Flight Ctr. (United States)
Laurel A. Rachmeler, NASA Marshall Space Flight Ctr. (United States)
Frédéric Auchère, Institut d'Astrophysique Spatiale (France)
Javier Trujillo Bueno, Instituto de Astrofísica de Canarias (Spain)


Published in SPIE Proceedings Vol. 10699:
Space Telescopes and Instrumentation 2018: Ultraviolet to Gamma Ray
Jan-Willem A. den Herder; Shouleh Nikzad; Kazuhiro Nakazawa, Editor(s)

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