Immersion grating is a next-generation diffraction grating which has the immersed the diffraction surface in an optical material with high refractive index of n > 2, and can provide higher spectral resolution than a classical reflective grating. Our group is developing various immersion gratings from the near- to mid-infrared region (Ikeda et al.^{1, 2, 3, 4}, Sarugaku et al.⁵, and Sukegawa et al.6). The internal attenuation α_att of the candidate materials is especially very important to achieve the high efficiency immersion gratings used for astronomical applications. Nevertheless, because there are few available data as α_att < 0.01cm^-1 in the infrared region, except for measurements of CVD-ZnSe, CVD-ZnS, and single-crystal Si in the short near-infrared region reported by Ikeda et al.7, we cannot select suitable materials as an immersion grating in an aimed wavelength range. Therefore, we measure the attenuation coefficients of CdTe, CdZnTe, Ge, Si, ZnSe, and ZnS that could be applicable to immersion gratings. We used an originally developed optical unit attached to a commercial FTIR which covers the wide wavelength range from 1.3μm to 28μm. This measurement system achieves the high accuracy of (triangle)α_att ~ 0.01cm^-1. As a result, high-resistivity single-crystal CdZnTe, single-crystal Ge, single-crystal Si, CVD-ZnSe, and CVD-ZnS show α_att < 0.01cm-1 at the wavelength range of 5.5 - 19.0μm, 2.0 - 10.5μm, 1.3 - 5.4μm, 1.7 - 13.2μm, and 1.9 - 9.2μm, respectively. This indicates that these materials are good candidates for high efficiency immersion grating covering those wavelength ranges. We plan to make similar measurement under the cryogenic condition as T ≤ 10K for the infrared, especially mid-infrared applications.

Date Published: 8 July 2014
PDF: 8 pages
Proc. SPIE 9147, Ground-based and Airborne Instrumentation for Astronomy V, 914738 (8 July 2014); doi: 10.1117/12.2055644

Published in SPIE Proceedings Vol. 9147:
Ground-based and Airborne Instrumentation for Astronomy V
Suzanne K. Ramsay; Ian S. McLean; Hideki Takami, Editor(s)