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Diamond-machined ZnSe immersion grating for NIR high-resolution spectroscopy

Yuji Ikeda (Photocoding), Naoto Kobayashi (Univ. Tokyo), Paul J. Kuzmenko, Steve L. Little (LLNL), Chikako Yasui, Sohei Kondo, Atsushi Minami, and Kentaro Motohara(Univ. Tokyo)
2008年6月27日 SPIE conference
"Astronomical Instrumentation" @Marseille
■ アブストラクト
ZnSe immersion gratings (n~2.45) provide the possibility of high-resolution spectroscopy for the near-infrared (NIR) region. Since ZnSe has a lower internal attenuation than other NIR materials, it is most suitable for immersion grating, particularly in short NIR region (0.8-1.4um). We are developing an extremely highresolution spectrograph with R = 100,000, WINERED, customized for the short NIR region, using ZnSe or ZnS) immersion grating. However, it had been very difficult to make fine grooves on ZnSe substrate with a small pitch of less than 50um because ZnSe is a soft/brittle material. We have overcome this problem and successfully machined sharp grooves with fine pitch on ZnSe substrates by nano precision fly-cutting technique at LLNL. The optical testing of the sample grating with HeNe laser shows an excellent performance: the relative efficiency more than 87.4 % at 0.633um for a classical grating configuration. The diffraction efficiency when used as an immersion grating is estimated to be more than 65 % at 1um. Following this progress, we are about to start machining a grating on a large ZnSe prism with an entrance aperture of 23mm x 50mm and the blaze angle of 70 deg.