D.I.Y. holographic photopolymer

Holography related topics.
Martin
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D.I.Y. holographic photopolymer

Post by Martin »

Getting access to the necessary raw materials (monomers, photoinitiators etc.) used to represent the main difficulty when making your own photopolymers. But now there exist several photopolymer systems from a host of different areas, from 3D printing, paint, to adhesives etc., which are readily available. I think they ought to be tested for holography. Since these are not designed to record holograms, they may require some fine-tuning though. So perhaps, D.I.Y. photopolymers for holography may be just right around the corner.

Whenever I got hold of a new UV adhesive (since the early 1990s), I had to verify its potential for holographic recordings. Back then, the only "success" I remember was a very dim transmission grating on a stuff from Loctite, exposed at 488nm. Later, when I used to have access to a sufficiently coherent 405nm laser diode, I was able to record transmission holograms of moderate brightness. The adhesive was sandwiched between two glass plates. That was on a new kind of adhesives, often sold as "liquid plastic" (under brand names like "Blufixx", "Smart Fix", "5 seconds fix" etc. They all look very similar or even identical. They are pretty interesting. The curing takes place at an outstanding speed. A couple of years ago, I noticed that liquid post-processing with alcohol etc. greatly enhanced the DE of a transmission grating. So yes, they definitely can be fine-tuned into a holographic recording material.
These relatively new UV adhesives are largely hydrophobic. Hence the addition of hydrophilic ingredients is limited. This puts some restrictions on the initiators/binders to be used.

Recently, I once more tackled the transformation of a commercial UV adhesive into a holographic recording stuff. Due to the lack of a reliable 405nm laser, I switched to spectral sensitization. In order to make my adhesive red sensitive, I simply added a little bit of triethanolamine (free radical generator), some methylene blue (photoinitiator) and a binder (nitrocellulose).Since these mixtures are not optimized for holographic recordings, index modulation is moderate. I've a feeling though they may be further enhanced by other additives, perhaps a post-processing step. E.g. there are tons of binders to be tested.
As of now, I've yet to record a bright reflection hologram. So of course this system isn't quite on par with DuPont, Covestro (Bayer) or the photopolymers I co-developed at Polygrama back then. But for class-room demonstrations it would certainly be good enough. Moreover, contrary to the above mentioned commercial products, this new system is not vulnerable to aerial oxygen. So the photopolymer layer does not require a barrier film on top of it.
Din
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Re: D.I.Y. holographic photopolymer

Post by Din »

Martin, do you know why you can't record reflection holograms? Perhaps the mechanism of recording on these adhesives forms surface profiles, but not Bragg structures within the adhesive? Do you have any idea of the depth of the emulsion? I believe I mentioned to you at one time that one problem with reflection recording is that the ratio varies as a function of depth in the volume, so it may be a function of depth modulation. If so, perhaps you're getting a few good Bragg structures only.
Martin
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Re: D.I.Y. holographic photopolymer

Post by Martin »

Din wrote:Martin, do you know why you can't record reflection holograms?
Actually, I was able to record a reflection hologram - but its brightness wasn't very impressive, Dinesh.
Perhaps the mechanism of recording on these adhesives forms surface profiles, but not Bragg structures within the adhesive? Do you have any idea of the depth of the emulsion? I believe I mentioned to you at one time that one problem with reflection recording is that the ratio varies as a function of depth in the volume, so it may be a function of depth modulation. If so, perhaps you're getting a few good Bragg structures only.
Its viscosity being rather low, the adhesive on its own probably doesn't record a reflection hologram. That's where the choice of the binder becomes important. I guess numerous options exist in that area.
As for limited index modulation, it could well be that the refractive index difference between light and dark fringes is too low. That probably relates to the specific monomers mix which most likely isn't "optimized" for holography.

That said, I was extremely surprised to see a reflection hologram at all. It certainly must have been a lucky shot. I didn't really make consistent tests. I simply almost randomly mixed the stuff just to see what happens.

But given recent results, I think the strategy of modifying e.g. a commercial UV adhesive (I would be interested into looking into the 3D printer stuff as well!) looks highly promising.
dannybee
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Re: D.I.Y. holographic photopolymer

Post by dannybee »

Hi Martin I would be will to help you on this! I do have lots of free time which I can devote to this. can you share some in-depth Info .. so I can try this on my end :) thanks
Martin
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Re: D.I.Y. holographic photopolymer

Post by Martin »

dannybee wrote: Sat Jul 14, 2018 11:47 am Hi Martin I would be will to help you on this! I do have lots of free time which I can devote to this. can you share some in-depth Info .. so I can try this on my end :) thanks
Any support is appreciated, thanks Danny. This D.I.Y thing ought to be seen as an open source project probably. I think emphasis should be put on easily available materials. That implies relatively low toxic products as well.
jeff-blyth
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Re: D.I.Y. holographic photopolymer

Post by jeff-blyth »

Hi Martin, It has been known for a long time that you can only make transmission fringes i.e. perpendicular to the substrate when you start with a liquid that will then gel under laserlight. Those perpendicular fringes are then spatially anchored to the glass substrate like the teeth on a comb and the still liquid nodes or “NO Disturbance” fringes between teeth can flow away or be removed without spoiling that spatial integrity. But if you try to make reflection fringes running parallel with the glass then it is impossible for that vital spatial integrity of the gelled fringes to be maintained while you have them sandwiched between ungelled liquid nodes. Somehow you have got to have the material all gelled to start with and then able to be made even more gelled in the light struck anti-nodes so that their refractive index is greater than in the lightly gelled nodes… .….as demoed beautifully in DCG.
I guess that the UV curing systems out there are made deliberately so that it would be difficult to initially partially gel them. So for example the monomers are turned into polymers in a virtually binary fashion, they are either polymerized or they are not…….hm… I might have a go at seeing if I could do something myself about this. Perhaps by adding a bit of hydroquinone to the liquid resin to cut down the polymerization efficiency by shortening the pathlength of the free radicals so that a short bit of incoherent floodlight is enough to partially gel it before hitting it with your coherent laser set up and making hardened antinodes but the exposure times would have to be pretty long then.
Martin
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Re: D.I.Y. holographic photopolymer

Post by Martin »

Hi Jeff, good to see you here again!

You're absolutely right, the uv systems I mentioned don't quite look like a gel. That's why I added a "binder" like nitrocellulose etc. For the same purpose I equally tested a couple of traditional (solvent based) adhesives, epoxies, siloxanes, PU, methyl metacrylates etc. At the end of the day the most tricky part always came down to how to get a consistent transparent layer. This of course strongly relates to my use of triethanolamine (occasionally I used EDTA). I understand triethanolamine introduces a lot of water into the system. So to counter this, the binder has to be hydrophilic as well in part. In addition I found triethanolamine to be interesting since combined with these uv adhesives it provides very good photo speed).

Your idea of adding hydroquinone to control chain length sounds interesting. I'd like to give it a try this soon as I get access to a reasonably coherent 405nm laser diode.
dannybee
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Re: D.I.Y. holographic photopolymer

Post by dannybee »

a thought that keeps coming up in my mind, what about PVA UV Glue.. like "DELO adhesives and PVA Dispensing System"

I know when I was doing some work in pva it was easy to make refection holograms.

also I know in many old photographic 1880 they use Glycerin with gelation, I made a gel plate for my wife to use in her card making it was gel & gelation. also I think all 3 could work together . one time I took glycerin (that had a fragrance add)and add it to gelation and it became almost like a cling vinyl sheet. just some ideas
pluto
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Re: D.I.Y. holographic photopolymer

Post by pluto »

Somehow you have got to have the material all gelled to start with and then able to be made even more gelled in the light struck anti-nodes so that their refractive index is greater than in the lightly gelled nodes… .….as demoed beautifully in DCG.
What if you were to expose the entirety of the photopolymer to the expanded laser beam for a period of time right before the exposure? My thinking is that this would partially gel the photopolymer and allow reflection holograms to be recorded more effectively.
Martin
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Re: D.I.Y. holographic photopolymer

Post by Martin »

dannybee wrote: Tue Jul 24, 2018 12:04 pm a thought that keeps coming up in my mind, what about PVA UV Glue.. like "DELO adhesives and PVA Dispensing System"

I know when I was doing some work in pva it was easy to make refection holograms.
Of course you can easily make PVA (PVOH) based photopolymers. Previously, they used to be made with acrylamide mostly. In recent years there's been a rush to less toxic monomers. So the research groups in Dublin and Alicante tried to replace acrylamide with a less aggressive monomer.

There's also Jeff's system, www.researchgate.net/profile/Jeff_Blyth ... graphy.pdf and its corresponding video at https://av.tib.eu/media/21871).

In the context of D.I.Y. photopolymers these are very promising approaches - as long as you get access to the chemicals required.
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