Questions about two color holography

[Jeffrey Weil]

It was a simple question, Danny. I want to know if it can be taken further.

[dannybee]

It was a simple question, Danny.

and do you really care I don't think so ....sorry Joe and dinesh it just make me so angry at is arrogance

[dannybee]

It was a simple question, Danny. I want to know if it can be taken further.

yes I think so ....

[Holomark]

Thanks Danny, I understand now. The Melles laser would indeed be difficult for standard setup, with an elliptical, divergent beam. Just getting the green DPSS to approximate the HeNe was troublesome enough

I am now headed down the road of trying to get my green DPSS (315M) to match my (new) HeNe. After playing with this for only a very short time it appears that it is not too difficult to setup for single beam Denisyuk (I may even try to get some images this weekend!) (I do, however, wonder how they will turn out when the divergence rate of the two combined beams are not the same - will I get clear images with either one color or both)
However, longer beam path lengths involved with Transmission Holograms and split beam setups appear to be problematic because of the different beam diameters and divergence rates. For this I presume I need some optics befor the dicroic filter (to combine beams) to change the beam from the DPSS to match the HeNe. (I presume I want to expand beam to equal or exceed diameter of HeNe Beam then collimate (or match divergence of HeNe)) Any tips, tricks, or suggestions on how to accomplish this would be much appreciated.

[Joe Farina]

For your first color holograms, I would concentrate on simple, single-beam reflection (Denisyuk) holograms. You will have your hands full for a long time, as you struggle with the recording material. Also, I would focus on what is happening before and after the spatial filter. Make sure, by some means of your choice, that the entrance beams going into the objective are the correct size. Now check the output of the spatial filter. Be sure the center of the spread beam is adequately uniform to cover the area being recorded on the plate. It should be a clean mixture of green and red, in other words YELLOW. In my case, I have a little overspill of red in the spread beam. I don't know if this is due to mismatch of divergence, or is due to something else. I don't let this worry me, as long as the central portion is a clean yellow. I doubt that slight variations in divergence will have any effect on the hologram.

[Holomark]

A spatial filter is on my list of optics and other things needed. I can see that I need to find a way to tame (match with HeNe) my green diameter and divergence. I managed to get the beams relatively mixed. So I finally got to test my new toy last night/this morning. I started with a relatively simple object - a can of Coke. Didn't finish playing with beam shaping. I ended up with a very extreme angle on my reference and ended up with this:

first coke

first coke 2.jpg (32.45 KiB) Viewed 3549 times

first coke - left

first coke - left.jpg (29.24 KiB) Viewed 3549 times

The color looks fairly good, but the depth is fairly limited. Lots of work to do, but too little time in the lab. With a little luck I will have some more interesting holos.
Mark










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[Joe Farina]

Congratulations, you've made excellent progress! The red and white both look "real." I'm amazed that the colors came out so well, so soon. I had to do a lot more struggling before I got a decent result. I'm sure everybody is asking the question: What recording material are you using?

It's surprising that the white looks so white. I've noticed this also on some of the two-colors I've done. I would have thought it would look more "yellow" because the original spread beam looks yellow on a white subject. Maybe it has something to do with color desaturation in the reconstruction, but I don't know. The Coke can definitely looks red and white.

As much as I like Coke, it is far from being the best subject for tests. If you can't find a colorful, small, and stable subject, then I would suggest painting one yourself. I would put in as many colors as possible: browns, yellows, whites, reds, orange, greens, etc. I would leave out the blues, since that would probably just confuse matters.

Hope to see more!

[Dinesh]

It's surprising that the white looks so white. I've noticed this also on some of the two-colors I've done. I would have thought it would look more "yellow" because the original spread beam looks yellow on a white subject. Maybe it has something to do with color desaturation in the reconstruction, but I don't know. The Coke can definitely looks red and white.

It's not so much colour de-saturation as it's colour expectations. You expect to see white because you know what a coke can looks like. It's also to do with the gamut of his reconstruction beam.If he's reconstructing with a halogen lamp, due to the higher operating temperature, the colour temperature is shifted towards the blue with respect to a non-halogen lamp. This blue preponderance will give the appearance of white on reconstruction. This, helped by your expectation of white and the dark background, enhances the "whiteness". You can tell the difference (sometimes) by illuminating a white object on the hologram, for example, by showing a business card against the hologram.

That's not to say this isn't a pretty good first attempt at colour!

[Joe Farina]

It's not so much colour de-saturation as it's colour expectations. You expect to see white because you know what a coke can looks like. It's also to do with the gamut of his reconstruction beam.If he's reconstructing with a halogen lamp, due to the higher operating temperature, the colour temperature is shifted towards the blue with respect to a non-halogen lamp. This blue preponderance will give the appearance of white on reconstruction. This, helped by your expectation of white and the dark background, enhances the "whiteness". You can tell the difference (sometimes) by illuminating a white object on the hologram, for example, by showing a business card against the hologram.

Thanks Dinesh, that helps. I thought color expectations were probably involved, but hadn't considered the influence of the blue component in the reconstruction source. One thing seems certain: making color holograms is a lot easier than explaining or troubleshooting them!

[dannybee]

can you share technical info like, what film type, what lasers, how you mix colors, your processing....its very nice work