High-efficiency broadband polarization-independent binary fused silica gratings for large astronomical telescopes.

The binary fused silica gratings (BFSGs) with high diffraction efficiency are presented for large astronomical ground-based telescopes. Calculations demonstrate that the BFSGs could obtain high diffraction efficiency in a wider wavelength range and angle of incident (AOI) range compared with volume phase holographic gratings. Several gratings with a size of 60×60 have been fabricated by holographic lithography and reactive ion-beam etching technology. The measured peak diffraction efficiency reaches 94%, and results show that there are 130 nm wavelength bandwidth and 12° AOI bandwidth in which diffraction efficiency is higher than 70%. The stray light causes the diffraction efficiency to decrease by about 0.48%. All measurements have indicated good consistency with the simulation results.