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Proceedings Paper

Fabrication and current optical performance of a large diamond-machined ZnSe immersion grating
Author(s): Yuji Ikeda; Naoto Kobayashi; Paul J. Kuzmenko; Steve L. Little; Chikako Yasui; Sohei Kondo; Hiroyuki Mito; Kenshi Nakanishi; Yuki Sarugaku
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Paper Abstract

ZnSe immersion gratings provide the possibility of high resolution spectroscopy in the wide infrared wavelength region from the NIR (Near Infrared) to the MIR (Mid Infrared), because ZnSe has a high refractive index (n ~ 2.45) and a low internal extinction in these wavelength regions. We are developing ZnSe immersion grating for a ground-based NIR high-resolution spectrograph and a space MIR high-resolution spectrograph. We already have produced fine grooves on the ZnSe flat substrate with a small pitch (~ 30 μm) using nano precision flycutting technique at the Lawrence Livermore National Laboratory,1 which satisfies our requirements even for the short NIR application.2 Our next step is to fabricate a large prism-shaped ZnSe immersion grating with this technology. The triangle prism has the entrance surface 50mm × 23mm and the apex angle of 70 deg. Untile now, we tried three R&D cutting runs. We examined the optical performances of the immersion grating sample from the second cutting run, which showed the best performances. Although a lot of chipping are seen at the edge of the blaze by the microscopic observation, we found that the groove shape is quite good with the surface irregularity of 0.74λ (pv) and the random pitch error of 5.2 nm (rms), which closely meet with our requirements. In the HeNe laser spectra taken under both grism and immersion configurations, strong ghosts were observed at the intermedium of the diffracted orders. These interorder ghosts may originate from the differences of the pitch and/or shape between odd and even grooves due to the cutting procedures. In addition, we also investigated a suitable reflectivecoating for the diffraction surface. As a result, we concluded that aluminum or cupper by suppering process is the best materials in the wavelength region of WINERED. Finally, we discuss the pssible improvement points and prospect for the next trial in this summer.

Paper Details

Date Published: 20 July 2010
PDF: 11 pages
Proc. SPIE 7739, Modern Technologies in Space- and Ground-based Telescopes and Instrumentation, 77394G (20 July 2010); doi: 10.1117/12.856631
Show Author Affiliations
Yuji Ikeda, Photocoding (Japan)
Kyoto-Sangyo Univ. (Japan)
Naoto Kobayashi, The Univ. of Tokyo (Japan)
Paul J. Kuzmenko, Lawrence Livermore National Lab. (United States)
Steve L. Little, Lawrence Livermore National Lab. (United States)
Chikako Yasui, National Astronomical Observatory of Japan (Japan)
Sohei Kondo, Kyoto-Sangyo Univ. (Japan)
Hiroyuki Mito, Kiso Observatory, The Univ. of Tokyo (Japan)
Kenshi Nakanishi, Kyoto-Sangyo Univ. (Japan)
Yuki Sarugaku, Japan Aerospace Exploration Agency (Japan)

Published in SPIE Proceedings Vol. 7739:
Modern Technologies in Space- and Ground-based Telescopes and Instrumentation
Eli Atad-Ettedgui; Dietrich Lemke, Editor(s)

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