Developing the wide-spectral coverage, very high-efficiency grisms for MOIRCS on Subaru Telescope

The fabrication of the new medium-resolution grisms for MOIRCS onboard Subaru 8.2-m Telescope is presented. Our new grisms feature the state-of-the-art gratings that have amazing high efficiency and wide-spectral coverage manufactured by LightSmyth Technologies. The grating has the peak efficiency of over 96% and can cover the whole H-band wavelength range with over 90%. This is the first-time astronomical application case for the LightSmyth grating. We manufactured the custom-made H-band grism as well as the catalog product J-band grism. The cooling test of the grisms confirmed the stability of the wave-front error over the cooling cycle. On-sky performance test were achieved in July 2020, and we have confirmed the high sensitivity as well as the amazing flatness of the throughput of these grisms. We also confirmed that the anticipated ghosts by the 0-th order light does not affect to the science operation. We started opening the grisms to the Subaru community from August 2020.