dichromate tuning chart

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Updated: 2005-03-28 by HoloM (the god)

dichromate tuning chart

Post by Dinesh » Sun Jan 04, 2004 5:36 pm

I think it's a good chart as a basis. However, I also think it depends on how the plate is made. The primary cause of color playback, in the end, is the Bragg plane seperation. This depends on:

1. Situation before exposure
I'd say that film sensitivity and film thickness is the primary effect here. The former, I'd say, is obvious. In the latter case, light absorption through any medium is exponential. There is an absorption distance (usually denoted by 'alpha') such that the light intensity drops by 1/e, about a 1/3, every time the light crosses that distance. Let's say that for DCG, this distance is a micron (you can look this up - it should be in any reference book) and your reference beam is about 20 mW. Then you have 14 mW after the first micron 10mW after the second, then 7mW etc . If you're emulsion is too thick, the back of the emulsion is seeing only a tiny fraction of the reference beam.

2. Situation during exposure.
The efficency and color control will depend on the number of cross linking events in any Bragg plane and the overall cross linking throughout the emulsion. These cross linking events will depend on the ratio of dich/gel and their uniformity .The ratio of the cross linking in te Bragg planes to the cross linking throughout the emulsion will determine the hardness differential and so the efficency. The cross linking throughout the emulsion will depend on the "dark reaction" ie how old the plate is and will in turn determine how much the plate swells in the water.

3. Situation after exposure
In this case, the amount of overall cross linking and the amount of pre-hardening will determine the swell rate in the water. As you pass it through the various alcohols, the water is gradually extracted. The rate at which the water is extracted determines the replay color and bandwidth. The drying technique is also a water removal technique, as is the time before you seal it.

I think (I hope) that this information will help DCG holographers get a better grasp of the variables. I'm sure there are effects I've missed out on, but these are all I can think of now.