This paper reports experiments that confirm Belloni (2003) that pre-soaking a silver halide holographic emulsion in a dilute solution of the formate ion (HCO2-) will hypersensitize the emulsion by a factor of 5xs to 10xs, depending on the timing of development post-exposure. The quantum efficiency of the emulsion is effectively 1 in the first case. The extremely fine grain size of the holographic emulsion (Slavich PFG-01) is maintained and holographic image quality is excellent. When combined with a TEA pre-soak the expected TEA color shift is maintained. Appeared in Proceedings volume 10558 SPIE OPTO | 27 january - 1 february 2018. Practical holography xxxii: displays, materials, and applications.
This article reviews the range of emulsions, photochemistry, and processing techniques that have been proposed and put into practice for the successful mak- ing of display holograms. It covers various types of media including gelatin-based emulsions and photopolymers (it focuses on the former) and considers external factors that affect the final results. This is a compact review of the history of the field but focuses on the range of easily available commercial emulsions, as well as certain accounts of how to make holographic emulsions from scratch. It considers various combinations of developer, bleach, and redeveloper, which have been used to achieve the best of various trade-offs for such factors as resolution, contrast, dif- fraction efficiency, clarity, color quality, blackest blacks, and resistance to printout. It describes a recent advance in hypersensitizing holographic emulsions.