GEOLA Film for Beginner

[Alan Sailer]

Howdy All,

I'm after some beginner information to try out holography.

I have two lasers to try, an old JDS Uniphase HeNe. It's long, about 25 inches. Modern versions of this laser say output is about 20mW.

I also have two Crystalaser 532nm that may or may not be single mode. I'm think they are in the >20mW range.

I was planning on buying some GEOLA photo-polymer film to start.

The questions are;

1) which laser will give me the best starting point? I can set-up a iMichelson interferometer to check coherence length but at this point I am not sure exactly what this will tell me.

2) Is the GEOLA film usable for two color holography? This would be a possible end goal for my task.

3) What safe-light is good for this film? Yellow LED?

4) I have a nice Olympus 50X objective that I would like to use as a beam expander. I think I need a 10um pinhole for spacial filtering. Are there cheaper alternatives than the Thorlabs 80$ cost?

Thanks in advance for any answers. Judging from my reading of the forum there are lots of patient and helpful holographers on this forum.

Cheers.

[Joe Farina]

Hi, the HeNe should be a good starting point, if it has a reasonable amount of power (unfortunately the power of lasers is usually unknown unless a meter is available). The Crystalaser may work also. I would start with small holograms, say 2 X 2 inches or smaller. Bayfol is of course much slower than silver halide. A yellow safelight is good (I would use the minimum amount of safelighting). Bayfol is well-suited to 2 and 3 color holography. $80 doesn't sound too bad for a pinhole, others may know of less expensive alternatives. Hope this helps.

[jrburns47]

If you have a mount for the pinhole, National Aperture is a good source for unmounted pinholes.
https://www.nationalaperture.com/

[Alan Sailer]

Thanks all. The price on the unmounted pinhole is great. 45$. I'm sure that I can make a mount.

I'm going to order the film.

Cheers.

[Din]

Starting with the film, the polymer you have has a sensitivity of roughly 30 mJ in the red and green. If your lasers are about in the 20 mW range, then, depending on the kind of hologram you want to start with, this sensitivity will determine exposure times. For example, if you're starting with Single Beam Denisyuks (a common starting point) with these ~ 20 mW lasers, and assuming that you lose about 20% in the expanding optics, for a 10cm x 12 cm (4" x 5") film, you'll have 0.13 mW/cm² on the film and the exposure time is 30/0.13 ~ 230 secs or about 4 minutes. As Joe suggests - and I agree - if you start with a 5cm x 5cm (2" x 2"), then you'll have ~ 0.64 mW/cm² and the exposure time is 30/0.64 ~ 46 secs. The shorter exposure time will mitigate against any motion problems. However, since these lasers are old, they may not be giving out 20 mW, and your best bet is to shoot several smaller film with varying exposures; starting with about 40 secs and going up in increments of, say, 20 seconds. The answer to your question, then, is to start with either laser, but not both, conduct the exposure tests as per above, and judge the holograms against the exposure times. This may give you the actual power of your laser. Doing two colour shots is tricky because each laser "robs" the material of some power from the other colour, and the brightness depends on which laser you expose with first. Better to determine single laser exposures first, then move on to multi-colour.

As for the Michelson, you can determine the coherence length of either laser (but not both together!) by varying the distance of one mirror from the beamsplitter. As you observe the fringe structure, the contrast will reduce as the difference in distances increases. When the contrast goes from high contrast black/colour-of-laser to a light grey, the difference in mirror distances is the coherence length. If the interference pattern seems to be drifting slowly, then you have motion somewhere. If the interference pattern suddenly 'jumps' - a sudden shift in the pattern - then the laser is mode hopping.

A dim yellow/orange safelight is best. I used an orange led, and turned up the resistor to limit current so as to keep the led dim.

There are a variety of outlets for cheaper equipment and components. Two of these are Lightglass optics ( https://www.lightglassoptics.com/ ), and siskiyou ( https://siskiyou.com/?gad_source=1&gcli ... gIQlfD_BwE ). Lightglass optics resells other optical manufacturers, eg Newport. at lower prices.

[Alan Sailer]

Din,

Thanks for all the information.

Yes my initial try will be with the HeNe since I think it has a better chance of success. A very old laser power
meter seems to say it's putting out ~20mW.

The two laser thing is a stretch goal depending on what happens with a single laser. Based on what I have read
here and in other places the difficulties with multiple laser holography scale exponentially.

Based on the Geolo data I picked a 570nm LED safelight. I plan to aim it at the ceiling in my garage. It appears to give a
dim but usable light in my work area. It's near the human eye max sensitivity...

Cheers

[Alan Sailer]

I got the film today. I am trying to avoid stupid mistakes so I will ask simple questions.

I ordered larger sheets and plan to cut them smaller.

1) What would be a good beginner size plate given about 25mW 532nm to expose?
2) Do I need to open the Geola envelop under safelight? In other words is the film inside the shipping package light tight?
3) is it easy to figure out which side of the film is the strip off plastic? ie the part that you remove to laminate the film to glass.
4) any suggestions for a simple light tight container to store the final laminated plates?

Cheers.

[Din]

]

1) What would be a good beginner size plate given about 25mW 532nm to expose?

While it's largely a personal choice, I'd say roughly about 4in x 4in (10cm x 10cm). The reason is that you need to do some exposure tests for the best exposure. The smaller the test film, the less you waste on tests. However, if you make the test film too small, you won't get a good view of the surrounding noise - you need to have some "blank space" around the image to see the effect of noise.

I asked Joy (wife) about the rest of your questions, since she's the practical engineer (I'm more theoretical ). Here are her answers

2) Do I need to open the Geola envelop under safelight? In other words is the film inside the shipping package light tight?

Generally yes. The film may be wrapped in a light proof envelope(s) inside the box, so to withdraw the film from the envelope, you need a safelight.

3) is it easy to figure out which side of the film is the strip off plastic? ie the part that you remove to laminate the film to glass.

Joy's technique is stick some scotch tape in a corner of the film and draw on the scotch tape to separate the two sides. The film will have a tint, while the cover will be clear, or may be frostred.

4) any suggestions for a simple light tight container to store the final laminated plates?

Joy had two suggestions:
Use tinfoil, but don't re-use the tinfoil. Wrap with fresh tinfoil every time you remove one film. The reason is that the tinfoil may create pinholes in the film.
If the film comes in a black envelope, take all the film from one envelope and put it in the other. Then use the empty black envelope to put unexposed but laminated film. You may be able to buy a light-tight box from a photographers supply shop, if they still exist.

[Alan Sailer]

Din (and Joy),

Thanks so much. I had not thought of aluminum foil. I was thinking black plastic but feared that near IR could get through...

The tape idea is great. I have read that the photopolymer sticks like a post-it note so tape should be good.

That size sound good. It will let me make about 30 plates.

Cheers.

[Ukyzoom]

Howdy All,

I'm after some beginner information to try out holography.

I have two lasers to try, an old JDS Uniphase HeNe. It's long, about 25 inches. Modern versions of this laser say output is about 20mW.

I also have two Crystalaser 532nm that may or may not be single mode. I'm think they are in the >20mW range.

I was planning on buying some GEOLA photo-polymer film to start.

The questions are;

1) which laser will give me the best starting point? I can set-up a iMichelson interferometer to check coherence length but at this point I am not sure exactly what this will tell me.

2) Is the GEOLA film usable for two color holography? This would be a possible end goal for my task.

3) What safe-light is good for this film? Yellow LED?

4) I have a nice Olympus 50X objective that I would like to use as a beam expander. I think I need a 10um pinhole for spacial filtering. Are there cheaper alternatives than the Thorlabs 80$ cost?

Thanks in advance for any answers. Judging from my reading of the forum there are lots of patient and helpful holographers on this forum.

Cheers.

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