Methods for preparing laminar phase diffraction gratings of up to 400 lines per in. are described. The grating is copied photomechanically from a master amplitude grating and the phase-reversing layer applied by vacuum evaporation. Silica is used for transmission and chromium for reflection gratings, the resultant optical elements being extremely robust and of a high degree of uniformity.
A. E. ENNOS, "Preparation of Phase Diffraction Gratings by Vacuum Evaporation," J. Opt. Soc. Am. 50, 14-17 (1960)