Questions about two color holography

[Dinesh]

Thanks, Joe. Actually, the cross talk problem was a bit difficult, and I'm not sure we've completely solved it. We've found that if you bring in the three beams with a separation of at least 25 degrees all in one plane, then the cross talk images are far enough apart that a 4x5 H2 does not show the cross talk. I've heard techniques where the three beams are non-planar, even to the extent that the three beams are at right angles to each other. There's a drawing of a transmission full colour geometry by Rudy Berkhout with three beams all at right angles. I thought that this was going to be very difficult to set up, so I asked him about it. He told me that he'd never actually set up such a system, the geometry he drew was hypothetical. Hiroshi visited us a couple of years ago and saw our transmission colour H1's. He mentioned that there were researchers in Japan trying to do it with three beams all at right angles, so he said he was gratified to learn that you didn't have to do it - 25 degree planar separation was enough. Of course, it is possible to limit cross talk with a thicker emulsion, which dcg would allow you to coat. But, I've been trying for several years now to find a native red sensitive additive to make dcg red sensitive. I thought I had it when I tried adding Potassium Permanganate to the dichromate, but all that did was to shift the sensitivity to about 590 or so - a sort of orange. A bit whimsical perhaps, but it occurred to me that blood turns from blue to red when exposed to air, so was it possible to use the haem molecule? But, I still haven't bled for holography!

The problem really arises when you try to do an image planed colour reflection H2 from a colour H1. Your point as to beam divergences is the problem, unless the beam divergences of the H2 ref are exactly the same, the three images get displaced in the z direction and magnified by different amounts.

[Martin]

But, I've been trying for several years now to find a native red sensitive additive to make dcg red sensitive. I thought I had it when I tried adding Potassium Permanganate to the dichromate, but all that did was to shift the sensitivity to about 590 or so - a sort of orange.

I've been there too.
In connection to green sensitive DCG solutions, I even tried mixtures of dichromate/thiocyanate, which turn deeply red. I had to learn that light absorption doesn't necessarily translate into light sensitivity.
Incidentally, the addition of a tiny amount of ammonium thiocyanate to "regular" DCG seems to have a slight speed enhancing effect.

A bit whimsical perhaps, but it occurred to me that blood turns from blue to red when exposed to air, so was it possible to use the haem molecule? But, I still haven't bled for holography!

That might be something to try in a FEG system...

[Dinesh]

I had to learn that light absorption doesn't necessarily translate into light sensitivity.

I think that what you need is something with a high and low oxidation states such that an actinic reaction converts the higher state to the lower state. Then, the lower state must be able to charge couple with the local matrix. Just absorption may not lead to an actinic/conversion molecular reaction, but simply a re-arrangement of the outer shells a la the transition elements, creating anomalous dispersion.

The interesting thing about blood is that it clots. If this clotting can be enhanced optically, then it may be possible to use that same mechanism to create layers of different indices. This research ( http://www.bioopticsworld.com/articles/ ... r-off.html ) by MIT looks hopeful.

[Dinesh]

I had to learn that light absorption doesn't necessarily translate into light sensitivity.

Just absorption may not lead to an actinic/conversion molecular reaction, but simply a re-arrangement of the outer shells a la the transition elements, creating anomalous dispersion.

I was just thinking of this while shaving this morning. If absorption alone by the chosen compound (the thiocyanate) simply re-arranges the orbitals, is it possible to dope the substance with something that has intermediate energy levels. Thus, the chosen compound absorbs light causing a re-arrangement of the orbitals, then the dopant may absorb some of the electrons as they're re-arranging themselves which in turn may cause an actinic reaction in the dopant. The dopant would act as a sort of catalyst. The idea of the He in a HeNe laser acting as a sort of dopant to cause a meta-stable state brought this to mind.

[Martin]

If absorption alone by the chosen compound (the thiocyanate) simply re-arranges the orbitals, is it possible to dope the substance with something that has intermediate energy levels.

Yes, that would be the kind of mechanism I'd also hoped to find one day.

Thus, the chosen compound absorbs light causing a re-arrangement of the orbitals, then the dopant may absorb some of the electrons as they're re-arranging themselves which in turn may cause an actinic reaction in the dopant. The dopant would act as a sort of catalyst. The idea of the He in a HeNe laser acting as a sort of dopant to cause a meta-stable state brought this to mind.

Right, there are areas where that seems to work. E.g. doped silica nanoparticles come to my mind. I'm not sure if something like that is doable based on dichromates or ferric components.

[dannybee]

ther are 2 ways I have tried that can solve some of the cross talk and color saturation and beam mixing
1 first one I tried is a fiber lens this seams to solve the beam mixing because they don't have to be totally alined and then mask out after the fiber lens.
2 Is a lcd matrices in front of the plate, you can get this from a old lcd monitor as solves (cross talk and color saturation)

making film panchromatic sensitive is very easy to do by adding dye, now depending on grain size is weather you will have to ad orange or yellow dye post process to reduce the scattering of the blue light or this can be done by using the right bleach that will stain the final hologram to reduce blue scatter

[Dinesh]

ther are 2 ways I have tried that can solve some of the cross talk and color saturation and beam mixing
1 first one I tried is a fiber lens this seams to solve the beam mixing because they don't have to be totally alined and then mask out after the fiber lens.
2 Is a lcd matrices in front of the plate, you can get this from a old lcd monitor as solves (cross talk and color saturation)

making film panchromatic sensitive is very easy to do by adding dye, now depending on grain size is weather you will have to ad orange or yellow dye post process to reduce the scattering of the blue light or this can be done by using the right bleach that will stain the final hologram to reduce blue scatter

Is this for an H1 or an H2? For an H1 in colour, fibers would not have any advantage, since the beam sources have to be well separated angularly anyway. For an H2, fibers may solve the beam combining problem, since you don't need dichroic mirrors, but there are other practical problems. If the fibers are large (~10 micron), then they are not polarisation maintaining. Even though the two states have the same phase velocity, small birefringence in the material causes the polarisation to mix at points where the fibers bend. So, in the end, the polarisation state that comes out of the fiber isn't the one that went in, and the variation of polarisation is pretty random, depending on how it twists and turns. So, even of you put in all three lasers into the separate fibers at the same polarisation, they'd be different when they exit the fiber. If you use polarisation maintaining fibers, then they have small NAs. This means it's very difficult to launch light into them and the output is dim. Also, another problem may be that, for H2's (and assuming you use non-polarisation maintaining fibers to conserve light), the source of the three wavelengths are about a micron apart, or two lambda apart. This will cause, at best, fuzzy edges on the image, or, at worst, image separation.

The fiber technique may work if you're making a single- (well, triple-) beam Denisyuk of a diffuse object, since then each polarisation state can be different polarisation state and the object will depolarise anyway. But, as per the comment about source separation, you'd have to reconstruct the hologram with three different sources placed very close together - about the diameter of the fiber. Of course, you can alway reconstruct using the same fibers but using leds instead of lasers. Also, of course, if the fibers were a very long way from the object/plate, then the object/plate will see a single source of rgb, but you'll get p*ss poor light on the plate!

So, Danny, have you got an example of a hologram using this fiber technique?

[Joe Farina]

So, Danny, have you got an example of a hologram using this fiber technique?

I was wondering also.

[dannybee]

ther are 2 ways I have tried that can solve some of the cross talk and color saturation and beam mixing
1 first one I tried is a fiber lens this seams to solve the beam mixing because they don't have to be totally alined and then mask out after the fiber lens.
2 Is a lcd matrices in front of the plate, you can get this from a old lcd monitor as solves (cross talk and color saturation)

making film panchromatic sensitive is very easy to do by adding dye, now depending on grain size is weather you will have to ad orange or yellow dye post process to reduce the scattering of the blue light or this can be done by using the right bleach that will stain the final hologram to reduce blue scatter

Is this for an H1 or an H2? For an H1 in colour, fibers would not have any advantage, since the beam sources have to be well separated angularly anyway. For an H2, fibers may solve the beam combining problem, since you don't need dichroic mirrors, but there are other practical problems. If the fibers are large (~10 micron), then they are not polarisation maintaining. Even though the two states have the same phase velocity, small birefringence in the material causes the polarisation to mix at points where the fibers bend. So, in the end, the polarisation state that comes out of the fiber isn't the one that went in, and the variation of polarisation is pretty random, depending on how it twists and turns. So, even of you put in all three lasers into the separate fibers at the same polarisation, they'd be different when they exit the fiber. If you use polarisation maintaining fibers, then they have small NAs. This means it's very difficult to launch light into them and the output is dim. Also, another problem may be that, for H2's (and assuming you use non-polarisation maintaining fibers to conserve light), the source of the three wavelengths are about a micron apart, or two lambda apart. This will cause, at best, fuzzy edges on the image, or, at worst, image separation.

The fiber technique may work if you're making a single- (well, triple-) beam Denisyuk of a diffuse object, since then each polarisation state can be different polarisation state and the object will depolarise anyway. But, as per the comment about source separation, you'd have to reconstruct the hologram with three different sources placed very close together - about the diameter of the fiber. Of course, you can alway reconstruct using the same fibers but using leds instead of lasers. Also, of course, if the fibers were a very long way from the object/plate, then the object/plate will see a single source of rgb, but you'll get p*ss poor light on the plate!

So, Danny, have you got an example of a hologram using this fiber technique?

yes have to find image .... and yes this will only work with Denisyuk

[dannybee]

https://www.facebook.com/photo.php?fbid ... =3&theater picture of beams going into fiber lens
https://www.facebook.com/photo.php?fbid ... =3&theater Holo made with fiber lens