Some Discussions Regarding Gelatin-Based Holographic Plates

[whoiswei]

The photosensitive mechanism of gelatin dry plates fundamentally relies on photo-induced electron transfer, which causes gelatin cross-linking and subsequent refractive index modulation. Why is it that, among various gelatin systems, only dichromated gelatin (DCG) stands out, while diazo-gelatin and ferric-gelatin remain mediocre? Furthermore, why are there hardly any other alternative materials?
​Theoretically, one could consider a system utilizing persulfate combined with a transition metal complex that decomposes at specific wavelengths. Persulfates possess strong oxidizing properties, but this oxidation is typically activated only in the presence of transition metal ions. Based on this principle, such a system could theoretically achieve performance close to that of dichromated gelatin while remaining non-toxic. Moreover, given the infinite combinations of transition metals and ligands, there is bound to be a suitable formulation, meaning its potential for multi-wavelength optimization should theoretically be superior.
​Taking a more radical approach, why wouldn't photosynthetic pigments like chlorophyll work? In the photosynthetic electron transport chain, chlorophyll in the photosystem ejects an electron upon light excitation and subsequently strips an electron from water. This indicates that it also possesses exceptional electron-withdrawing capabilities under illumination. Theoretically, wouldn't it suffice to simply add a small amount of a weak oxidant to act as the "primary electron acceptor," mimicking its role in plants, to achieve a similar photo-crosslinking effect?

[jrburns47]

Speaking as a non-DCG holographer, your apparent understanding of the photochemistry involved seems much more sophisticated than the average skilled DCG holographer. Maybe it would be worthwhile for you to undertake the research to further develop your ideas.

[Din]

There are many materials that have been tried/used for holography besides silver halide and dichromates. The problem is that these 'holography' sites/forums/social media is dominated by display holographers, who simply use holography either for art or as a hobby. There are no sites, as far as I know, that discuss the more technical aspects of holography. To that regard, they're not interested in the more technical details of chemistry, physics and mathematics in holography. In many cases, some of them get extremely angry when technical details are discussed because they either think they understand - and don't - or they don't understand and get angry because they don't understand; they simply want only display holography discussed. This forum used to have a lot of technical discussions but those days are gone.

At any rate, yes, chlorophyll has been discussed and there are papers about the use of chlorophyll as a holographic medium. AT POC (Physical Optics Corp, where I worked in the 80's) we had a polymer chemist research new forms of polymer holographic material.There is also material based on retinal proteins using the fact that light generates an electrical signal from bacteriorhodopsin - the protein in the retina; the important thing is that, once the image is no longer on the retina, the retina "clears" the image and allows a fresh image on the retina to generate new signals. This allows for holographic data storage in holograms recorded on bacteriorhodopsin which the stored data can be wiped and re-recorded so creating a sort of holographic read-write memory (https://ieeexplore.ieee.org/document/606117). I have also thought of hemoglobin as a holographic material, since light turns the normally blue hemoglobin to red on exposure to light.

Komar ("Light Sensitive Systems") lists a variety of materials besides silver halide and dichromates (below)

Komar.jpg (886.19 KiB) Viewed 1970 times

[Din]

Also, from "Topics in Applied Physics" vol 20 - "Holographic Recording Materials, ed H. M. Smith below

Rec. Mat.jpg (239.85 KiB) Viewed 1970 times

[Manul]

The photosensitive mechanism of gelatin dry plates fundamentally relies on photo-induced electron transfer, which causes gelatin cross-linking and subsequent refractive index modulation. Why is it that, among various gelatin systems, only dichromated gelatin (DCG) stands out, while diazo-gelatin and ferric-gelatin remain mediocre? Furthermore, why are there hardly any other alternative materials?
​Theoretically, one could consider a system utilizing persulfate combined with a transition metal complex that decomposes at specific wavelengths. Persulfates possess strong oxidizing properties, but this oxidation is typically activated only in the presence of transition metal ions. Based on this principle, such a system could theoretically achieve performance close to that of dichromated gelatin while remaining non-toxic. Moreover, given the infinite combinations of transition metals and ligands, there is bound to be a suitable formulation, meaning its potential for multi-wavelength optimization should theoretically be superior.
​Taking a more radical approach, why wouldn't photosynthetic pigments like chlorophyll work? In the photosynthetic electron transport chain, chlorophyll in the photosystem ejects an electron upon light excitation and subsequently strips an electron from water. This indicates that it also possesses exceptional electron-withdrawing capabilities under illumination. Theoretically, wouldn't it suffice to simply add a small amount of a weak oxidant to act as the "primary electron acceptor," mimicking its role in plants, to achieve a similar photo-crosslinking effect?

Add organic photoinitiators, and it will cross-link like a photopolymer.

[whoiswei]

There are many materials that have been tried/used for holography besides silver halide and dichromates. The problem is that these 'holography' sites/forums/social media is dominated by display holographers, who simply use holography either for art or as a hobby. There are no sites, as far as I know, that discuss the more technical aspects of holography. To that regard, they're not interested in the more technical details of chemistry, physics and mathematics in holography. In many cases, some of them get extremely angry when technical details are discussed because they either think they understand - and don't - or they don't understand and get angry because they don't understand; they simply want only display holography discussed. This forum used to have a lot of technical discussions but those days are gone.

At any rate, yes, chlorophyll has been discussed and there are papers about the use of chlorophyll as a holographic medium. AT POC (Physical Optics Corp, where I worked in the 80's) we had a polymer chemist research new forms of polymer holographic material.There is also material based on retinal proteins using the fact that light generates an electrical signal from bacteriorhodopsin - the protein in the retina; the important thing is that, once the image is no longer on the retina, the retina "clears" the image and allows a fresh image on the retina to generate new signals. This allows for holographic data storage in holograms recorded on bacteriorhodopsin which the stored data can be wiped and re-recorded so creating a sort of holographic read-write memory (https://ieeexplore.ieee.org/document/606117). I have also thought of hemoglobin as a holographic material, since light turns the normally blue hemoglobin to red on exposure to light.

Komar ("Light Sensitive Systems") lists a variety of materials besides silver halide and dichromates (below)
Komar.jpg

Oh，thank you very much！
I can't believe these things actually work! It's absolutely amazing, this is so cool!