Continuing to Raise the Technical Readiness of Germanium Immersion Gratings for a Space-based High-resolution IR Spectrograph

The technological advance that reduces the size and mass of an IR spectrograph for a future space mission is a high index-of refraction Germanium (Ge) immersion grating. To date, a Ge grating with adequate clarity, thermal stability, and geometric precision to serve as this key optical element within such an instrument has not been available. Two of these gratings were manufactured at Lawrence Livermore National Lab (LLNL) using funds from a 2016 CIF. Our plan was to obtain these gratings in FY16 with time to conduct optical tests in the lab. The procurement process for the elements required to fabricate the gratings consumed most of the year and the team focused instead on being ready to execute testing on our warm/cold optics bench in FY17. In this 2017 CIF, we plan to focus on three questions to demonstrate the feasibility of Ge Immersions Gratings for future space-based instruments: 1) Do current gratings deliver the spectral resolution required with line profiles free from ghosts? 2) Are Ge immersion gratings efficient enough to deliver ground-breaking new science from a small satellite? 3) Do the gratings and their optical coatings perform well at low temperatures required for IR instruments?