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Dispersing elements are the key device of the spectrometer. Spectrograph in SPACE has various limitations at size and weight. An immersed grating and GRISM, which is made of high-index material is effective in solution of those problems. First, an absolute efficiency of dispersing element is very important, because the throughput of spectrograph has big relation with the mirror size that is almost equal with a scale of a satellite. When an immersed grating or GRISM made of high-index material with high-throughput is manufacturing, there are many difficulties as the fact known well. Especially it is difficult to obtain the ideal grooved shape and a sufficiently small surface flatness. CANON has already succeeded in the development of a practical Germanium (Ge) and Indium phosphide (InP) immersion echelle grating. On the other hands, about CdZnTe immersed grating, it was only succeeded in processing of grooved shaping on the immersed prism. There was not a back-reflection coating on the grooved surface, which was indispensable in order to obtain a high- efficiency. In this development, a back-reflection coating on the grooved surface for CdZnTe immersed grating has succeeded. Two devices for an actual proof shows very good absolute maximum diffraction efficiency (>75%) and small polarization dependability (< 1%). Since the back-reflection coating is a gold base, it is possible to apply in 10-20μm which range of wavelength is main objective in use of CdZnTe. Moreover, a machined Germanium/Indium phosphide GRISM also has succeeded. This GRISM is a type of transmittance. The grooves on GRISM were machined with a diamond tool. Manufacturing some GRISMs with different resolution, the minimum grooved pitch is about 2.2 μm. These GRISMs have the efficiency and the surface flatness compared with a ZnSe GRISM known before. As the conclusions, these devices are useful to the space application, and becomes indispensable to a high-performance spectrograph.
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