In early February, the iLocater team took delivery of another key piece of hardware for the iLocater spectrograph: an optimized echelle diffraction grating. This grating, a loan unit manufactured by Canon Japan/Canon U.S.A., Inc, will help to support the integration and testing of the iLocater spectrograph. iLocater uses two gratings within the spectrograph to spread out light into its constitutent colors, allowing them to be recorded by the instrument detector. The echelle grating is the primary and most important of these two gratings.
The loan grating is a prototype of a future grating which will be delivered to the iLocater program as part of a NASA Astrophysics Research and Analysis (APRA) grant which was awarded to the program. Manufactured from the intrinsically stable metal IC-DX (a variant of Invar), the grating is plated with front and rear surfaces with copper. This allows for direct ruling of a high performance optical surface on the front (low wavefront error and high-efficiency), which is subsequently gold coated to further optimize performance. The plated rear surface supports optimized cryogenic operation.
Delivery of the grating allows further optical testing of the spectrograph to be completed, while also demonstrating the performance of the grating technology in cryogenic high-resolution spectroscopic applications.