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 αatt 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 αatt < 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)αatt ~ 0.01cm-1. As a result, high-resistivity single-crystal CdZnTe, single-crystal Ge, single-crystal Si,
CVD-ZnSe, and CVD-ZnS show αatt < 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.