<title>Dichromated gelatin (DCG) masters for single-beam photopolymer copies</title>

Abstract

The dynamic recording range or the maximum index modulation obtainable in any holographic material limits the properties of the hologram. The product of the modulation times the thickness determines diffraction efficiency in any phase hologram. In a reflection hologram low uniform modulation yields narrow spectral and angular bandwidths and high modulation in a chirped siructure yields high angular and spectral bandwidths. An ideal master hologram requires a just right efficiency and very low noise to produce the best possible copies. In a two beam copy scheme the efficiency is less important than the low noise because beams can usually be balanced to the just right range with a variable beam splitter. In a single beam copy scheme the balance and the low noise plus wide enough angular and spectral responses all have to be built into the master. DCG has all the right properties for a top quality master that will get the most from any copy film of marginal index modulation, single beam reflection copies in Dupont photopolymers are as bright as the material will allow in any copy configuration. THE COMPETITIVE EDGEThe subject matter recorded in a display hologram is in my opinion and experience the number one determinant of its value and its salability in the commercial market place. Ranking in a close second place is its general appearance which includes color, noise, clarity and brightness. In third place we could put batch uniformity, a problem that never quite goes away but for those that mass produce in Dupont polymers it has become manageable. I am not aware of any particular problems with silver grain production or embossed replication and most of the advantages of a DCG master can be exploited in those media as well.All else being equal then the competitive commercial advantage goes to the enterprize that can produce the best masters. The best masters for production in blue or green light are made in DCG. It has the lowest scatter and the highest modulation potential of all the materials I know of. On the other hand, Dupont film could be described as the most user friendly and DCG has earned the title of the most user surly. My purpose here and over the years is to help make it more friendly for those that need the edge. The DCG methods for making masters are fairly simple and the following notes combined with prior teachings listed in the references are designed to provide every little necessary trick of the trade to get any holographer well under way. 84 ISPIE Vol. 2333 O-8194-1666-5/95/$6.oo Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/23/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx