Improving the remarkable photosensitivity of dichromated gelatin for hologram recording in green laser light

J. Blyth
University of Cambridge, UK
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The UV–Visible range absorption spectrum of unexposed dichromated gelatin film (DCG) shows almost no absorption by the dichromate ion at 532 nm. By using a post exposure baking step with a small quantity of glycerol we have managed to produce bright holograms with light energy levels below 50 mJ per cm2. This is better than has been achieved with the aid of dyes in DCG and perhaps better than has been achieved so far with any photopolymer system using 532 nm light. Also using 514 nm light from an argon laser, we have achieved a 4 fold increase in photosensitivity over that obtained using conventional procedures. We postulate that this increase in photosensitivity may be the result of an actual amplification of the changes caused by the laser light, and that this effect does not occur in the traditional method using Kodak Rapid Fix plus Hardener. The experimental method detailed here is written with the amateur holographer in mind now that for example powerful green 532 nm cw lasers are readily available at much lower cost. A particular additional feature about the method is the use of potassium dichromate and specifically not the traditional ammonium dichromate.