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Long time no see, Jeff! Glad to see that you are still following the forum, Kaveh told me at Photonics West that you were having medical issues, I hope you beat it, TJ had a similar case and he did!

I have a different question for you, see the AgX section.

After playing around with “dichromating” various polymers over the years, I have found that gelatin gives the highest sensitivity among polymers which are available. Why this should be I have concluded as follows:
The initial real driving force in the reaction LIGHT+DICHROMATE +POLYMER is the oxidizability of the polymer chain. There are bits and pieces in the complicated gelatin molecules that make them much more oxidizable than the simpler PVA molecules . (Actually also I found that the higher the residual polyvinyl acetate content in the PVA the worse was its oxidizability apparently, so you need the “fully hydrolysed grades”. ) .
So at least 2 or 3 times more light exposure is needed on PVA/ dichromate mixes than gelatin ones. What the oxidizable groups are in gelatin that make it particularly effective I am not sure of , but almost certainly the sulfur groups must be important such as –SH in the amino acid cysteine. The more cysteine present the better , and that could depend on say the number of buttercups the old cows munched up!

I think the worst problem with PVA though is the difficulty in getting a good coating because its water solutions have a high surface tension and unlike gelatin they don’t wet clean glass well. I needed to use as much alcohol in the mixes as I could without precipitating out the PVA. In the article mentioned by Martin above I did go into that as well as using a silanized PVA to make it stick. But I was not using dichromate as crosslinker there.
Jeff Blyth

In which context and how were the results?

i have worked with PVA

profdc9 wrote: Supposedly DCPVA produces a much stronger latent image than DCG. In addition, DCPVA is heat tolerant, so it can be fixed with heat (with some penalty in diffraction efficiency). Fixing with heat might have fewer problems with fringe shrinkage and hologram blueshifting, and be easier for home holography.

One big issue with heat processing seems to be that it involves rather thick layers only. Obviously, index modulation is pretty low.
In the case of reflection holograms heat processing yields fairly moderate DE.

Liquid processing in turn was said to produce DCG-like qualities. That's at least what Richard Rallison pointed out in his paper, Recipe for Dichromated Polyvinyl Alcohol (DC-PVA), SPIE 3358. Stojanoff (http://silvercrossproject.org/news_info ... 0final.pdf) mentions carboxylic PVA ("The film holographic properties compare well to DCG.").

A big disadvantage of DCPVA is that PVA sticks poorly to glass.

From Jeff Blyth's paper about his latest liquid photopolymer system (here's the video: http://river-valley.tv/pva-photopolymer ... olography/) I learned there was a special kind of PVA available from Kuraray. It contains some silane groups, making it stick on glass very strongly.

Hello Dan,

First of all, welcome to the forum. I don't have first hand experience with DC-PVA, just some thoughts. After reading some papers concerning the topic, i noticed that in most areas, at least as far as display holography is concerned, PVA doesn't seem to offer any key advantages over DCG:

- low DE
- low sensitivity
- difficult handling / processing (temperatures, coating, can't remelt)
- price / ease of acquirement

Concerning the robustness, DCG can be quite robust too if processed accordingly. Some of Rallisons gratings have been exposed to high energy radiation corresponding to an exposure in space for years without degradation of performance. For a more earthly application, a ninhydrin treatment is supposed to virtually remove DCGs sensitivity towards humidity.

For real time applications the preferences are different of course and PVA may have its advantages there.

Ahmet

Hello,

I was wondering if anyone here has experience with dichromated polyvinyl alcohol and could compare it to dichromated gelatin. There are a few reasons I am interested in it:

1. Supposedly DCPVA produces a much stronger latent image than DCG. In addition, DCPVA is heat tolerant, so it can be fixed with heat (with some penalty in diffraction efficiency). Fixing with heat might have fewer problems with fringe shrinkage and hologram blueshifting, and be easier for home holography.

2. DCPVA might store better. It is apparently a fairly robust material as detailed somewhat in this military report:

http://www.dtic.mil/cgi-bin/GetTRDoc?AD ... tTRDoc.pdf

3. A big disadvantage of DCPVA is that PVA sticks poorly to glass. I was considering sandwiching the DCPVA emulsion between two glass plates. If one fixes with heat, this is no problem as no further access to the emulsion is required. If the corners of the plates were epoxied together, the plate could be placed into alcohol bath and the fixing could perhaps proceed slowly as the alcohol wicks between the glass plates.

A lot of the real-time aspects of DCPVA are explored in this paper (unfortunately not freely accessible)
http://www.opticsinfobase.org/abstract. ... 29-29-4384

Anyways I am just curious to find out what other people know and think about DCPVA.

Thanks,

Dan