Why GEOLOA photopolymer

[Alan Sailer]

I have been using the photopolmer for all of my experiments and am curious
what its actual commercial use is. It's seems to be cheaper than film but
require longer exposure times. I have not used film but the GEOLA stuff seems
pretty easy to scratch and would require encapsulation to protect it.

I could see it used like Polaroid film was used back in the 70-90s, as an
exposure check before taking normal film exposures.

Just curious what it is for. Not important to anything I am doing.

Cheers.

[BobH]

The primary use is for HOEs because it is panchromatic, has high diffraction efficiency with very low shrinkage, and doesn't require wet processing. It's also stable in sunlight. Geola and Liti are resellers of Covestro's material.

[Alan Sailer]

I'm new to the term HOE. A quick look implies that it is a hologram used as a optical product, like a lens
rather than being used for artistic purposes.

Thanks for the reply.

Cheers.

[Din]

Bayer launched its film in about 2009(?).

In around the late 80's/early 90's, Du Pont polymer was being used for security applications - credit cards and the like. I think the reason was that, because it didn't need wet processing, the production timelines were shorter.It was in this period that Agfa, the only silver halide film in common useage, stopped producing it. I remember at ABNH, I was tasked for finding a replacement for Agfa, and I called TJ. At any rate, a lot of people went over to polymer, mostly for security. At the time, ca 1990, all the technical applications were on DCG. In fact, I and Chris Rich set up the DCG lab at POC. Then, Du Pont disappeared; I heard rumours that De La Rue - the biggest producer of security holograms - had bought out all the Du Pont film to maintain a stanglehold on security holograms, whether true or not, a lot of people believed it. Just about then - mid 2000's, Bayer introduced a photopolymer film to fill in for the loss of Du Pont. Fuji also had a polymer and went around asking people to test it; we tested it for free but other people got paid to test it. Then Fuji disappeared. Just about then, Bayer introduced their polymer, mainly for security applications. Also, about then, a lot of technical holographers were trying polymer because it didn't need wet processing. Bayer kept a tight hold, and demanded to know what people wanted to do with it, which created a problem, because a lot of technical holography was under NDA's and non-competes. I was working with Javid Khan - Holoxica - and he implored me not to tell anyone we were working with Bayer. Then Microsoft came to us with a polymer application. Pretty soon, Bayer realised that their film was being used more for technical holograms, and switched from security to technical, calling the film Covestro. Display holographers wanted a crack at display (fair disclosure, we've never made a display on covestro) and initially, Covestro was hesitant. Then, they released it, so long as you bought an entire roll (expensive!). I have no idea what the situation is now, having been retired since 2017.

Covestro has advantages and disadvantages. It's very narrow-band and difficult to tune wavelengths in. This arose because many applications required holograms to 'capture' digital video from a digital diplay device, but the colour space for digital display is different from laser wavelengths . Also, digital displays are wide band (relative to laser wavelengths). In display holography, you can sweep this problem under the rug - the eye forgives a lot! - but when the hologram is designed to be machine read, it presents a difficulty.

So, to answer your question, Joy (wife) uses Covestro as Senior Optical Design Engineer, which seems to be it's main application in my field. I know some of you display holographer use it with variable success.

[Din]

I'm new to the term HOE. A quick look implies that it is a hologram used as a optical product, like a lens
rather than being used for artistic purposes.

Thanks for the reply.

Cheers.

HOE - Holographic Optical Elements. The idea is that you use holography to create/combine various optical components. Since glass is heavy, and working with large slabs of glass makes the product very heavy, a holographic optics can be lightweight, fast, cheap and multi-functional.

For example, one of my tasks in around 1987 was to make "laser protection goggles". The idea was that you'd make this hologram that was very, very clear in ordinary light, but the efficiency shot up 99.99% efficiency (not based on polarisation, thank god! Otherwise the function of the hologram would be useless, if the laser attacker simply changed the polarisation state of the the attack laser!). When worn in standard light, the glasses were crystal clear (there's a parameter known as the Photopic efficiency which determines how clear the glasses were.)But, when attacked with a laser, the hologram would instantly "go black", as 99.99% of the laser light would be rejected.

Over the years, they've been used for AR/VR/MR goggles, near-to-eye-displays etc .

[Alan Sailer]

A follow-up question.

So if Geola film is used to make HOEs, (presumably for further use) how do the final
users deal with a fragile, easily scratched film that barely sticks to glass support plates?

If seen users on this forum use screen protectors to laminate the hologram but what do
commercial users do to protect such a fragile film?

Cheers.

[BobH]

Sandwich it in glass with optical adhesive. For example, Ceres and Zeiss are putting the material into windshields for use as head-up displays. Pictorial holograms also are best sealed, but shrinkage of the adhesive will be the issue to deal with because of the weak bond of photopolymer to substrate. Adhesive used to strengthen that bond can't affect the photopolymer and most do.

[Alan Sailer]

BobH,

Do they peel it before that? Or just use the original glass and a new cover piece?

Cheers.

[BobH]

Don't know. Peeling it off the original mount that replaced the cover sheet may be difficult. It's a thick volume material so keeping the film exactly as flat as it was during recording is important.

[Din]

It depends on the application and the manufacturing process.

Take for example a HUD on a windscreen. When Joy (wife) was working in Luminit, in their research dept, one of her projects was to make HUDs for car windscreens. She slapped the film directly onto the windshield, and recorded it while on the windscreen itself - the entire windscreen was placed on the table.. The windshield was then placed into a car for demonstrations purposes at some conference trade show. Understand, the HOE, the hologram itself, is simply a reflective optic. A digital projector on the dashboard creates the image, which is then sent upwards to the HOE, and so into the viewer's eyes. She says that a car windscreen is composed of layers of glass and plastic sheeting. One of the layers of plastic sheeting is replaced by the hologram. It's quite possible, therefore, to embed the hologram into the windscreen during the manufacturing process, then record while the material is in the windscreen.

In another application such as VR (Virtual Reality), the idea is that you wear a pair of glasses and see "virtual information" fed to your eyes and superimposed onto the real world. Applications include the medical field and the automotive industry. In this case, there are holograms on either end of a channel called a 'diffractive waveguide'. The image, from some digital image device, is fed into an 'input hologram' at one end of the waveguide, which then sends the image along the waveguide using total internal reflection (TIR). At the other end of the waveguide is an 'output hologram' which sends the image into the viewer's eyes (https://www.uploadvr.com/content/images ... age-05.png). The holograms themselves are recorded remotely (not on the waveguide) and then inserted onto the ends of the waveguide. One of the first such VR goggles was by a Canadian company called North (Joy worked on these AR waveguides for North). North was later acquired by Google ( https://www.theverge.com/2020/6/30/2130 ... se-acquire )