Safelight

[Martin]

I do not see in the "traditional" polymerization method, the chain reaction is a triggered mechanism that will not stop in vinyl acrylate systems until termination, on other side in cationic ring open mechanism (epoxies), due the heat sensitivity, the total polymerization can be delayed at some extent that we can talk in latent image formation here.

Yes. In some cases the post-processing (heat, UV exposure, liquid processing) substantially enhances DE. So the "latent image" may simply be a weak image.
By the way, isn't that equally the case for dichromated systems?

[Dinesh]

[quote:6a6707ef34] By the way, isn't that equally the case for dichromated systems?[/quote:6a6707ef34]
Yes, I believe so. I seem to remember reading somewhere that an exposed but unprocessed DCG is about 2% effiicient. I once tried putting such a hologram in a spectrophotometer but could get nothing substantial. This equipment was designed to read holograms of OD 4 so it's resolution was too low for a 2% DE!
I wonder then, if you overmodulated such systems, is it possible to vary the DE of the latent image?

[Sergio]

I do not see in the "traditional" polymerization method, the chain reaction is a triggered mechanism that will not stop in vinyl acrylate systems until termination, on other side in cationic ring open mechanism (epoxies), due the heat sensitivity, the total polymerization can be delayed at some extent that we can talk in latent image formation here.

Yes. In some cases the post-processing (heat, UV exposure, liquid processing) substantially enhances DE. So the "latent image" may simply be a weak image.
By the way, isn't that equally the case for dichromated systems?

I do not agree, the DCG mechanism, simply a crosslinked molecular effect is all done with the actining radiation, the firmly crosslinked region is all there, what the phase shift enhancement mechanism, isopropyl treatment, do is fill with voids the soft region, it can be done with (Polaroid material) polymers.

So the latent image is not simple with polymers, the key is with the photoinitiator mechanism coupled with some thermal one etc. In DCG, what would be interesting is enhance the molecular crosslinking with with a more SOFT gelatin; aiming the DC react more with gelatin groups?

[Sergio]

By the way, isn't that equally the case for dichromated systems?

Yes, I believe so. I seem to remember reading somewhere that an exposed but unprocessed DCG is about 2% effiicient. I once tried putting such a hologram in a spectrophotometer but could get nothing substantial. This equipment was designed to read holograms of OD 4 so it's resolution was too low for a 2% DE!
I wonder then, if you overmodulated such systems, is it possible to vary the DE of the latent image?

But you did measure the phase variance between crosslinked and uncrosslinked region, right? The difference is too small for crosslinked polymers.. still this is not the case of a latent image, the overmodulation does not occur only in the development? I think so.

[Martin]

I do not agree, the DCG mechanism, simply a crosslinked molecular effect is all done with the actining radiation, the firmly crosslinked region is all there, what the phase shift enhancement mechanism, isopropyl treatment, do is fill with voids the soft region, it can be done with (Polaroid material) polymer

...I was also thinking of dichromated PVA that has strong real-time efficiency and which can be enhanced by heat treatment.