The chemical bleaching of absorption holograms produces phase holograms that exhibit higher light efficiency than the holograms from which they were produced. The bleaching of thick absorption type hologram diffraction gratings produced at 6328 Å is discussed. The bleached holograms were read out at both 6328 Å and 9100 Å. Ten bleaching materials were tried, of which two were judged acceptable: mercuric chloride and Kodak Chromium Intensifier. Mercuric chloride bleach produced efficiencies of 49% at 9100 Å and 37% at 6328 Å. The experimental results are compared with the maximum theoretical efficiencies by defining a grating efficiency, which is the ratio of the actual hologram efficiency to the intensity transmission of the hologram.
John N. Latta, "The Bleaching of Holographic Diffraction Gratings for Maximum Efficiency," Appl. Opt. 7, 2409-2416 (1968)