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Fabrication and evaluation of reactive ion-plasma etched astronomical diffraction grating with anti-reflective surface nanostructures

We fabricated nanoscale random anti-reflective surface structures on a prototype Reactive-Ion Plasma-Etched (RIPLE) grating. The prototype is a binary-profile, 1767 l/mm linear structure, over a 25x25 mm2 area on a ¼-inch thick Quartz plate, E-beam patterned, imbedded into the substrate by a Reactive-Ion Etching process. We achieved an 8:1 aspect ratio between the grating’s phase depth and space-width (187nm wide). The measured 1st-order unpolarized diffraction efficiency reaches 94.5%~96% and stays greater than 70% across a 200nm bandwidth centered at 560nm wavelength. The non-patterned side was populated with AR nanostructures. We detail the fabrication and evaluation of this complete prototype RIPLE grating.