Realization of optical/near IR ZnS immersion grating for next generation large telescopes

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We developed ZnS immersion grating which is a main disperser for the next generation optical/NIR high resolution spectrograph attached to the ground-based 30m telescopes and/or large space telescopes. Using a fly-cutting technique with the nano precision machining equipment in LLNL, we obtained the grooves on the CVD-ZnS prism with the relative diffraction efficiency of 72.8% at 1 um. And, we succeeded to fabricate the new reflective Cu coating with a SiO2 protection and anti-reflection thin-layer between the ZnS bulk and Cu, which achieved the high reflectivity over 90% from 0.8 to 1.5um. Therefore, we have a prospect of realizing the ZnS immersion grating for optican and NIR astronomical application.