Questions about two color holography

[Dinesh]

One thing seems certain: making color holograms is a lot easier than explaining or troubleshooting them!

Well, it's really the availability of multi-wavelength lasers. When I started, all I could get in England about 1982 was a Rofin HeNe about 0.7mW. Heck, I remember Goldfinger say, "This is a laser Mr. Bond. It can project a spot on the moon. At closer distances, it can cut through solid metal" ("Do you expect me to talk?" "No, Mr Bond. I expect you to die!" Be-e-eautiful! I still rank 'Goldfinger' up there with 'Citizen Kane', 'The Third Man' and 'The Godfather'. But I digress) Anyway, when I got to college, around 1972, and we were covering Laser Theory, the professor brought out a tiny little thing that could barely show up as a dim red dot on a wall about 6 feet away. I thought to myself, "That can project a spot on the moon???" Today, lasers in the 450 - 690 range are easily available and I have a uv led for about 20 bucks! So, while colour holography should be and is far more than simply zapping something with three wavelengths, you can get quite a decent result if you do simply that - throw three wavelengths at something. I think that colour holography has a greater mystique attached to it than it's due.

Mark, I'd like to know what material you're using also.

[Holomark]

The current setup uses 2 lasers - 315M putting out 100mW at 532 and HeNe putting out 45+mW at 623. To combine beams I am using a dicroic filter with green straight through and red reflecting. The combined beam passes through a shutter, then two lenses to expand beam and 1 mirror to change beam direction toward plate and object. 1 kicker mirror was used on the left side of object.
The recording material is Ultimate 08 and Ultimate Developer and Bleach were used.
The reconstruction was achieved with the use of a LED in the form of a Redline flashlight. The hologram was not painted or otherwise worked on after development and just thrown into a frame for handling. the flashlight was placed with the business end on the frame aimed parallel to the face of the plate. (I missed the angle I was trying to get and ended up with the reference beam almost directly above the plate.
I will not going to be satisfied with single beam holograms for very long, but I can already see some of the issues related to more complex setups. I got a bit lucky with my first attempts to combine the beams, but was not so lucky last night when I tried to change the angle of the object beam to plate. I ended up with uneven distribution, spotting, and shadow from optics. I think I need to buy some Hummous on the way home because there are a lot of PITA (pain in...) tasks involved in color holography.
First, I think I need to figure out how to tame the 315M beam, then I can work on combining beams, then spreading beams, and even illuminationof subject/plate, then split beam configurations. At the same time I am trying to change the beam spread at the plate to work with LEDs at close range (wih or without a lense). In my mind this is best don with split beam configuration as the wide dispersion of a single beam lacks depth because the lighting of objects decreases with distance.
Thank you for both the compliments and information. I am certainly open to other tips, tricks, suggestions or donation of optics or equipment (I probably wouldn't turn down a donation of cash either).
Back to my day job.
Mark

[Joe Farina]

So, while colour holography should be and is far more than simply zapping something with three wavelengths, you can get quite a decent result if you do simply that - throw three wavelengths at something. I think that colour holography has a greater mystique attached to it than it's due.

I agree. There seems to be a lot of resistance to even green and red, which is not that expensive. The rudiments can be learned with just those two lasers, and blue can be added later.

[Joe Farina]

First, I think I need to figure out how to tame the 315M beam

Mark, get your whip and chair ready, here's how to do it:

Use three lenses in a zoom telescope arrangement. See the thread called "co-linear beams, matching diameter and divergence." This was from the old forum in January of 2007. For reference, I used the book called "A History of the Photographic Lens" which describes zoom lenses in detail.

I assume my C-315M (100mW) has similar beam diameter and divergence, compared to yours.

My SP-127 beam diameter is 2.5mm at 8 feet, and 3mm at 12.5 feet. My beamsplitter on the isolation table in the other room is about 5 feet (estimated, not measured) from the dichroic mirror which combines the beams on the laser table. The 315M exit window is about 2 feet (again estimated) from the dichroic, and the 127 exit window is about 6 inches from the dichroic.

In the photo below, the 315 is on the left, the beam attenuator is next, then Lens 1, Lens 2, Lens 3, and finally a half wave plate. The focal lengths are as follows: Lens 1, 27mm; Lens 2, -57mm, Lens 3, 53mm. You will notice that Lenses 2 and 3 are rather close together, and I had to make an extension to the clumsy Thorlabs mount for Lens 3 to get it close enough to Lens 2. The focal lengths of the lenses and the distances were determined by a lot of trial and error. I bought a large selection of different lenses from Surplus Shed. All of the optical components are mounted on a Thorlabs rail, rail carriers, post holders, and posts. The lens mounts are homemade. The rail and mounts make things a lot easier.

Your mileage may vary, based on differences in equipment, optics, and distances in your lab. I strongly suggest trial and error, rather than attempting to think it out.

[Holomark]

The color on this one came out a little richer than than expected (object has almost pastel paint). The blotchiness is a litte more evident and green is a little too heavy.

Cher

Cher 2.JPG (29.76 KiB) Viewed 3090 times

I really like hr rosy cheeks. The skin tone is painted peachy, and not exactly uniform.
I now think I need a second shutter to assist in controlling exposure at each wavelength. I suppose I could thow a variable beam splitter on green to control intensity (reduce) of green beam to get the correct mix, but I just hate throwing that light away.
Now, I am on my way to take the employees to blow some glass! - fun "holiday event".