Novel gratings for astronomical observation

The choice of transmission grating can facilitate downsizing of a spectrograph and make it possible to achieve a perfect Littrow configuration. We are developing transmission gratings for next-generation instruments for the 8.2 m Subaru Telescope, the Thirty Meter Telescope (TMT), and other ground-based and space-borne telescopes. These include, a volume binary grating developed for an echelle grism (direct vision grating) for the Subaru Multi-Object InfraRed Camera and Spectrograph (MOIRCS); a reflector facet transmission (RFT) grating, a surface relief grating with sawtooth-shaped ridges of an acute vertex angle, expected to be deployed for the TMT Wide Field Optical Spectrograph (WFOS), and a hybrid grism for use as a medium-dispersion grism in MOIRCS, developed as a prototype of RFT grating. We describe the simulation results, fabrication methods, and experimental results of these prototype transmission gratings in this article.