Can I make a green hologram with a red laser?

[Tyler20002015]

I started playing with my new Litiholo hologram kit and I read somewhere that holograms made with a red laser can turn out green because of something called the Bragg effect. Is there any way I can do this with this kit or will the self-developing plates not allow it?

[Din]

The colour of a hologram is mostly a processing effect, not a recording effect.

When you make a hologram in the traditional way with modern materials, what you're actually doing is recording a set of planes inside the material; like slats on a window blind. These planes are the "data" of the hologram. However, the separation of the planes (the inter-planar distance) will determine the colour of the hologram. The effect of choosing a particular colour dependant on the planar separation is known as The Bragg Effect, or Bragg selection. Generally, the planes will be separated by half the wavelength of the recording colour. So, if you're recording with a red laser with a wavelength of 670nm, the planes will be recorded at a distance of 335 nm. But, when you develop the film, there will be a further separation of these planes, usually called emulsion swelling, or a contraction of the planes, called emulsion shrinkage by holographers. So, if you start with the recorded planar separation of 335nm and, after development, want to end with a green hologram with a plane separation of, say 257nm (ie 257x2 = 514nm) , you'll need to process it in such a way that the emulsion will shrink from 335 to 257

Is there any way I can do this with this kit or will the self-developing plates not allow it?

This kind of planar separation is relatively easy and quite controllable with wet processing. But I suspect that with a dry processing method, such as Liti, you won't get such a large change in planar separation. If you want a green hologram, shoot the Liti with a green laser, assuming that it's sensitive to green. I believe some here have made full-colour holograms on Liti, which means it should be sensitive to green. You need to get a green laser; a member of this forum - 142laser - sells lasers and may help you choose a green one.

[lobaz]

Hi, Tyler20002015,
as Dinesh pointed out, it is quite easy to produce "false color hologram" with silver halide holographic plates (i.e. "wet processing"). If you really want to try it, order some from e.g. Integraph, Harman or Ultimate (or even from unixboy at this forum who sells his own). Lots of chemicals are quite easy to get; ask here if you are confused where to begin. (Look for "pre-swelling", "post-swelling" and "solvent bleach".)

I have also no idea how to make a false color reflection (Denisyuk) hologram with self-developing material included in LitoHolo kit. I assume you are not talking about transmission hologram - you can illuminate a transmission hologram with whatever laser and you get a decent image in the color of the laser (there will be some aberrations but not too serious for a display hologram). You can e.g. make a red transmission hologram and illuminate it with a green laser LED.

You mentioned "the Bragg effect". You can easily observe it with LitiHolo kit as is. Make a reflection hologram of a shallow object with red reference beam hitting the plate at an angle say 30 degrees. If you watch this hologram under direct sunlight (use sunlight for first experiment, not e.g. white LED with uneven spectrum) at an angle 30 degrees, you should see the red image. However, if you illuminate the hologram at a different angle (turn it up and down) and watch it from different angles, you should observe color change of the image.

By the way, as far as I know most cheap green lasers (e.g. green laser pointers) are not able to produce a hologram. You need a special one designed for interferometry/holography. Remarkably, most cheap low-power red laser LEDs are capable to produce hologram - this is why most holography starter kits include red laser.

Petr

[Sergio]

Hi, Tyler20002015,
as Dinesh pointed out, it is quite easy to produce "false color hologram" with silver halide holographic plates (i.e. "wet processing"). If you really want to try it, order some from e.g. Integraph, Harman or Ultimate (or even from unixboy at this forum who sells his own). Lots of chemicals are quite easy to get; ask here if you are confused where to begin. (Look for "pre-swelling", "post-swelling" and "solvent bleach".)

I have also no idea how to make a false color reflection (Denisyuk) hologram with self-developing material included in LitoHolo kit. I assume you are not talking about transmission hologram - you can illuminate a transmission hologram with whatever laser and you get a decent image in the color of the laser (there will be some aberrations but not too serious for a display hologram). You can e.g. make a red transmission hologram and illuminate it with a green laser LED.

You mentioned "the Bragg effect". You can easily observe it with LitiHolo kit as is. Make a reflection hologram of a shallow object with red reference beam hitting the plate at an angle say 30 degrees. If you watch this hologram under direct sunlight (use sunlight for first experiment, not e.g. white LED with uneven spectrum) at an angle 30 degrees, you should see the red image. However, if you illuminate the hologram at a different angle (turn it up and down) and watch it from different angles, you should observe color change of the image.

By the way, as far as I know most cheap green lasers (e.g. green laser pointers) are not able to produce a hologram. You need a special one designed for interferometry/holography. Remarkably, most cheap low-power red laser LEDs are capable to produce hologram - this is why most holography starter kits include red laser.

Petr

You can produce a false colour on photopolymer by adding a small quantity of solvent onto formulation. After hologram recording with red laser WL you bleach the photoplate with light and remove the protective layer. The included special solvent will evaporate and given an emulsion shrinking to deliver a green image per example. This eliminate the necessity of any chemical development.. even you can write patters or designs onto film with locally dropped solvents..inkjet printed, this method is current patented by Polygrama company.

[lobaz]

This is interesting, Sergio. I have no idea how photopolymers work, so my question is likely silly: any photopolymer is covered by a protective layer? How can I remove it? Does any photopolymer contain some amount of "solvent" that can evaporate?
By the way, could you recommend me a resource where to learn basic facts about photopolymers in holography?

[142laser]

oh cool Sergio....never heard of this!

[Sergio]

This is interesting, Sergio. I have no idea how photopolymers work, so my question is likely silly: any photopolymer is covered by a protective layer? How can I remove it? Does any photopolymer contain some amount of "solvent" that can evaporate?
By the way, could you recommend me a resource where to learn basic facts about photopolymers in holography?

Yes, Practically all emulsions need this protective cover to protect from the dust and oxygen. Oxygen will affect the mechanism of polymerization and the cover forms a barrier from it during polymerization exposure..

The cover is easy removed after polymerization or bleaching etc. The you have the hologram ready. No commercial photopolymer have this solvent introduced onto emulsions as far I know. As a resource I recommend the excellent Hans book Ultra-Realistic Holography, include even pulsed laser photopolymer info!

[Din]

By the way, could you recommend me a resource where to learn basic facts about photopolymers in holography?

Here you go, Petr (If you follow the references, there's probably quite a lot of material relating to polymers for holography):
https://www.osapublishing.org/view_arti ... %3Dno&org=

By the way, page 6 of the paper, second para, has something interesting, per Sergio's comment on oxidation:

We note that it is assumed that the oxygen concentration which diffuses into an uncoverplated (not sealed) layer of the photopolymer can never be larger than the original concentration of issolved oxygen present in the layer, Z0 (mol/cm3) and that this additive term is assumed to be spatially constant.


But, if the oxygen is diffusing in from outside, wouldn't the oxygen concentration be a spatially exponential function, and not constant? And, if such a oxygen diffusion did occur after the cover was removed, and, it was exponential, then the effect would be worse for reflection holograms than transmission holograms. This is because the largest amplitude of Bragg planes occur at the first surface; the recording light attenuates as it goes through the emulsion, decreasing the Bragg plane amplitude.

[lobaz]

Thank you, Dinesh, I think I will start with Practical Volume Holography. It seems photopolymers are described there for real beginners.