Mounting HX200 for Cylidrical Holograms

[Alan Sailer]

I 'm getting another batch of photopoymer tomorrow and one of the things I want
to try are cylindrical holograms. The question is a good way to support the "film".

The only details I have read about this are to curl the film into the center of the
cylindrical support and wait a few hours to let the film settle down. Sounds like
wishful thinking to me.

Cheers.

[jrburns47]

Suggest starting small, that is a clear glass cylinder several inches in diameter. Clear plastic will work as well. Here’s one on eBay:
https://www.ebay.com/itm/167041524447?m ... media=COPY

Measure the internal circumference and cut film to length about 1/8th to 1/4” less than measurement. Height of film should be only maybe 3” for first test. Wrap film around interior circumference emulsion facing inward. Tape down one end and gently push film with fingernail until it’s snug against glass all the way around and tape that end to the glass as well.

Assume you will use a single diverging beam to both illuminate the the object as well as provide the reference beam for the film?

I would use tracing paper in place of the film to get setup aligned and desired film placement where you want it. Then cut the film to size etc. Good luck.

[Alan Sailer]

Thank you. So the tension of the photopolymer is good enough without lamination? I also
assume that you don't pull of the protective film?

Cheers.

[jrburns47]

Actually, wasn’t thinking clearly re photopolymer. Was only thinking of AgX film. Sorry. Interesting problem. Since photopolymer is used mostly for reflection holograms (meaning the Bayfol can be exposed via either surface), as well as transmissions sometimes, I don’t see why you wouldn’t be able to peel and apply inside the cylinder or even outside with the usual bubble/dust caveats. Should work either way, I would imagine, depending on your preference. I’m assuming that you’ll be making laser viewable transmissions that could be played back with a small diode laser. Could be quite a nice little item. If you look at the available eBay cylinder I linked to, since its considerably longer than it is wide, I don’t see why you couldn’t cut it into several shorter cylinders - either yourself or have a local glass shop do it for you. You would want to have the cylinder edges “polished” so no sharp edges.

[Alan Sailer]

Thanks. I have the glass cylinder part already solved. laminating flat is already difficult enough
that trying to laminate inside a cylinder seems like a mini nightmare.

Cheers.

[Din]

We did it with two beams, one from above, relative to the object - a biplane in this case, and one from below. The one from below was the reference, and the above lighting was for the object. In the picture below the object lighting was from the left, and the ref from the right. In the inlay, I show our ref and object lighting.

If you use a single beam, then you may have to illuminate with a laser diode, as Jody suggests. But, if the object's furthest distance from the material to the material - presumably the radius of the cylinder - is about a couple of inches or so, then it may be possible to light with an led; remember I'd earlier mentioned that you can illuminate an H1 with an led and, with an object-plate distance of about 6", you get a fuzzy image, but with an object-material distance of about a couple of inches, it may be more clear. Also, with a single beam geometry, I'd choose the object carefully. You want the object light to fairly illuminate the length of the cylinder all around, ie illuminate as much of the cylinder as possible. If you chose a biplane, as we did, all the object light will go up, and none of it to the lower part of the cylinder. I'd suggest a symmetrical, conical-type object like a cone or a pyramid.

One issue you have to be careful about is the beam divergence of the illumination. If the beam divergence of the reference beam and the illumination beam are mismatched, you'll get distortions; distortions in a plane geometry are not too bad, but distortions in a curved geometry will be noticed.

biplane_resize.jpg (21.51 KiB) Viewed 526 times

[Din]

And, the result.

I sent a pic of the biplane hologram to Alec Jeong (son of TJ - a legend in holography). Alec showed it to his dad, who then asked me how I did it. Here is a copy of the emails that passed between TJ and myself detailing our procedure, and possible problems.

"It's a super-bright LED. The problem is to match the reconstruction beam divergence to the reference beam divergence. As you know, if the two beam divergences are not the same, you get aberrations. In a small, flat hologram these aberrations are not serious, but on a curved surface, the distortion is much more obvious. So we first got a super-bright LED, then measured its beam divergence, then matched the reference beam to that divergence. We only matched the inner bright area's divergence since the laser is Gaussian and a LED beam is not Gaussian. The base is on a dark plastic so the "zero order" direct ligth is hidden. The nice thing about a LED is that they're very bright and narrow band with no heat output.

Hello Dinesh:

Thank you for copying me about your cylindrical hologram. My first publication in 1966 was on 360 deg. Holography, so I have a long time interest in this area and want more details.

Is your water glass coated with dichromate, or is it a hologram recorded on film and pasted on the glass? I presume it is a transmission hologram since the lighting is inside. Where is the location of the LED?

Thanks for your response.

TJ

Hello TJ

No, not a DCG. It's silver halide (Slavich VRP M). I'm sending a picture of the geometry.

I placed the biplane inside a cylinder and brought a beam from outside the cylinder and underneath the biplane so it spread inside the cylinder and around the biplane. That is, I placed the spatial filter so that it was along the axis of the cylinder but outside it. I then lit the top of the biplane simultaneously from the other side of the cylinder. Then I wrapped a film on the outside of the cylinder. After exposure and development, I replaced the film on the outside of the cylinder and lit it with a LED from the underside of the cylnder where the original spatial filter was.

The two problems were the beam divergence and attaching the film. If the beam divergence of the LED did not match the beam divergence of the reference beam the aberrations became more serious for a curved geometry. So I measured the beam divergence of a bright LED and placed the spatial filter at the appropriate position outside the cylinder so that the beam divergence of the reference beam inside the cylinder matched the beam divergence of the LED. Keeping the film steady on a curved surface without scatter was a challenge. If I used a transparent substance like "saran wrap", it acted like a "light guide" and the internal reflections within the saran wrap would have caused a lot of noise. Eventually I used sorbothane and it worked.

I actually had a paper on a theory of non-linearity inside holographic emulsions based on Kogelnik. Perhaps I could give it at the next ISDH.
Dinesh"

holo-plane2.jpg (20.2 KiB) Viewed 526 times