We report on the grating development for the High Efficiency and Resolution Multi Element Spectrograph (HERMES).
This paper discusses the challenges of designing, optimizing, and tolerancing large aperture volume phase holographic
(VPH) gratings for HERMES. The high spectral resolution requirements require steep angles of incidence, of 67.2
degrees, and high line densities, ranging between 2400 and 3800 lines per mm, resulting in VPH gratings that are highly
s-polarized that push the fabrication process to its limits.