Testing of a germanium immersion grating

Germanium Immersion Gratings (GIGs) may be an important component for a compact, high-resolution spectrograph for the infrared. Germanium’s large index of refraction reduces the length of the grating by a factor of four compared to conventional reflection gratings. Germanium transmits light from roughly 2 to 11.5 μm, which includes spectral regions largely unavailable from the ground because of molecules in Earth’s atmosphere. This combination makes GIGs a compelling technology for space missions focused on molecules in astrophysical environments. We are beginning testing of a GIG supplied by Canon, Inc., and anticipate eventual detailed testing of the Canon grating and a similar GIG supplied by LLNL. We also discuss potential science observations that demonstrate the significance of high-resolution, infrared spectroscopy from space.