Surface-relief gratings with anti-reflective nanostructures for panchromatic astronomical low/medium/high resolution spectroscopic surveys

Volume Phase Holographic Grating (VPHG) technology provides efficient dispersion solutions for astronomical spectroscopy, but its fabrication and parameter control remain in the realm of nonlinearity. More accurate and repeatable control can be achieved using micro-lithographic patterning processes and reactive-ion plasma etching (RIE), to fabricate surface relief gratings, free from surface defects and completely embedded into the substrate material. Such gratings promise potential for low/medium resolution spectroscopy applications not only in usual ground-based spectrographs, but in those subject to much harsher conditions (e.g. space-based, cryogenic, high-power laser instruments). When combined with nano-textured anti-reflective surfaces using the same fabrication technology, the relief gratings can serve astronomical spectroscopy needs that may be sub-optimally met or not feasible with VPHGs. We detail prototype micro-lithographic grating fabrication results in this paper.