Dr. Hiroko Watanabe Profile

Dr. Hiroko Watanabe

at Kyoto Univ

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Publications (2)

Proceedings Article | 7 October 2011 Paper

Ly-alpha polarimeter design for CLASP rocket experiment

H. Watanabe, N. Narukage, M. Kubo, R. Ishikawa, T. Bando, R. Kano, S. Tsuneta, K. Kobayashi, K. Ichimoto, J. Trujillo-Bueno

Proceedings Volume 8148, 81480T (2011) https://doi.org/10.1117/12.893241

KEYWORDS: Polarization, Wave plates, Polarimetry, Magnesium fluoride, Beam splitters, Modulation, Prototyping, Transmittance, Ultraviolet radiation, Refractive index

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A sounding-rocket program called the Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) is proposed to be launched in the summer of 2014. CLASP will observe the solar chromosphere in Ly-alpha (121.567 nm), aiming to detect the linear polarization signal produced by scattering processes and the Hanle effect for the first time. The polarimeter of CLASP consists of a rotating half-waveplate, a beam splitter, and a polarization analyzer. Magnesium Fluoride (MgF2) is used for these optical components, because MgF2 exhibits birefringent property and high transparency at ultraviolet wavelength. The development and comprehensive testing program of the optical components of the polarimeter is underway using the synchrotron beamline at the Ultraviolet Synchrotron Orbital Radiation Facility (UVSOR). The first objective is deriving the optical constants of MgF2 by the measurement of the reflectance and transmittance against oblique incident angles for the s-polarized and the p-polarized light. The ordinary refractive index and extinction coefficient along the ordinary and extraordinary axes are derived with a least-square fitting in such a way that the reflectance and transmittance satisfy the Kramers-Krönig relation. The reflection at the Brewster's Angle of MgF2 plate is confirmed to become a good polarization analyzer at Ly-alpha. The second objective is the retardation measurement of a zeroth-order waveplate made of MgF2. The retardation of a waveplate is determined by observing the modulation amplitude that comes out of a waveplate and a polarization analyzer. We tested a waveplate with the thickness difference of 14.57 um. The 14.57 um waveplate worked as a half-waveplate at 121.74 nm. We derived that a waveplate with the thickness difference of 15.71 um will work as a half-waveplate at Ly-alpha wavelength. We developed a prototype of CLASP polarimeter using the MgF2 half-waveplate and polarization analyzers, and succeeded in obtaining the modulation patterns that are consistent with the theoretical prediction. We confirm that the performance of the prototype is optimized for measuring linear polarization signal with the least effect of the crosstalk from the circular polarization.

Proceedings Article | 6 October 2011 Paper

Overview of Chromospheric Lyman-Alpha SpectroPolarimeter (CLASP)

Noriyuki Narukage, Saku Tsuneta, Takamasa Bando, Ryouhei Kano, Masahito Kubo, Ryoko Ishikawa, Hirohisa Hara, Yoshinori Suematsu, Yukio Katsukawa, Hiroko Watanabe, Kiyoshi Ichimoto, Taro Sakao, Toshifumi Shimizu, Ken Kobayashi, Brian Robinson, Tony Kim, Amy Winebarger, Edward West, Jonathan Cirtain, Bart De Pontieu, Roberto Casini, Javier Trujillo Bueno, Jiri Stepan, Rafael Manso Sainz, Luca Belluzzi, Andres Asensio Ramos, Mats Carlsson

Proceedings Volume 8148, 81480H (2011) https://doi.org/10.1117/12.894290

KEYWORDS: Magnetism, Polarization, Magnesium fluoride, Mirrors, Wave plates, Solar processes, Rockets, Spectrographs, Scattering, Telescopes

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