Swelling of Dichromated Gelatin Film

[Joe Farina]

Thanks for your comments, Dinesh, about fringe structure in a display hologram vs. a HOE (and also about the TMG). This ties in well with what I've been reading recently. The more papers I look at, the more I realize they're almost always talking about HOEs.

I purchased a paper which deals with fringe deformation in DCG, to a limited extent. I paid $46 for it (no other way, other than a trip to Chicago or Ann Arbor). I've attached the first 3 pages below. I would include the entire paper, but I don't want to deprive anyone of the privilege of patronizing Taylor & Francis. (Dinesh, if this has any interest to you, I will send the full 12 pages.)

I do get frustrated with lurkers, because there are so few participants here.

[Dinesh]

Dinesh, if this has any interest to you, I will send the full 12 pages.)

If this talks about fringe deformation, then yes please, I'd like the rest of it. There never seems to be anything on fringe deformation, just fringe translation and, sometimes, rotation.

[Joe Farina]

sent

[Tony DCG]

I have done some informal dark reation studies. Frankly I haven't seen a huge difference. 5 minutes seems more than enough although I have heard of those who go as long as 24 hours. Most of the dark reaction seems to occur within the first 1-2 minutes. I might go longer if I am making a master and need maximum brightness.

As for red masters. I use less AmDi (I can look at my notes as to how much) and works only with a green laser. I could never seem to get red with my blue system. It is tricky and they are generally dim but have tuned it to 650nm or so.

Nice infomation Joe, interesting read.

[Tony DCG]

From the Rallison section of the wiki: "Control of DCG and nonsilver holographic materials":

"The direction of the shift can be controlled by the ratio of alcohol and water in the first bath and the amount of shift can be controlled by the time in the same bath. A near ideal tuning bath has a specific gravity of .86 when it is warmed to about 55 degrees C. This process can be repeated many times if necessary, especially if the last hot bath is not hot enough to cause excessive scattering center buildup. Multiple buffer baths between the first color control bath and the last dehydration bath help to keep the last bath clean."

In tuning narrow band there are many factors such as fix time, film age, film thickness, exposure time and others. 70% (specific gravity of .86) is a good starting out point from there you can go two ways. If the wavelength is not where you want it to be you can tune with by reprocessing the plate using IPA/H2O concentrations or you can use heat to tune it. Both ways have their pros and cons.

[Joe Farina]

In another thread, I had mentioned that Sjolinder had included a graph (in the above paper on swelling) showing that pH didn't have much of an effect on gelatin swelling, unless it was quite high, or quite low. But I failed to notice that his gelatin layers were highly pre-hardened by a 2-hour bake at 150C. There is another paper called "The sorption of soluble dyes by gelatin" (1941) by Sheppard et al. which shows the swelling curves for unhardened gelatin (which is what I'm using for MBDCG). This shows a completely different picture, and is also markedly different for types A and B. The two graphs are below, the first one from Sjolinder, the second one from Sheppard.