Progress on edge-lit HOEs

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Dinesh

Progress on edge-lit HOEs

Post by Dinesh »

Arturo wrote:
Dinesh wrote:The area of the exit beam - the diffracted beam - is the same as the coverage from the original laser beam on the table. My aim in this is to launch light at the edge of the plate and have a focused beam come out of the face. In other words, to act like a lens, but without light coming in from the other face of the lens.
So, given a plate has four edges, you might (theoretically) use three for different colors and have a curious color combiner for your R, R & B lasers... ?!?!? (not to be taken seriously, you could write a whole encyclopedia with all I ignore about optics/holography, but this seemed right, once you overcome the technicalities ;) ).
Funny you should say this. I have a student who wants to do an extended study for extra credit. She's a Physics major with a Visual Arts minor. This is one of the suggestions I made to her. The major problem is film sensitivity. I can make a hologram in red, with a red laser, and have it reconstruct in green. This is possible with film swelling, angular tricks etc etc. In these cases, you take advantage of the Bragg selectivity. But, in an edge lit, are the "fringes" Bragg fringes, or surface fringes. Is the diffraction Bragg or Raman-Nath? I don't know (yet). Also, I can't use my usual angular tricks for altering colours, since there's only one angle I can use - the (almost) TIR angle. Yes, I can alter the material so I can change the TIR angle, but not by that much. Standard commercial pan film has a fixed emulsion thickness on standard glass, so I can't use that. Bayer is too thin, it doesn't come on glass. So, I have to have a red sensitive dcg. Some years ago, I tried to find an additive for dcg that would make it red sensitive without dyes, because dyes make the film too insensitive. I tried a whole set of materials and thought of a whole lot more (including haemoglobin!). I got some promising results using copper salts and managed to redshift the sensitivity of dcg towards green with a combination of copper salts and potassium permanganate. In the end I had to drop it because I had to do the work for the "DCG as Resist Medium" paper for the Holopak conference. Perhaps I might pick it up again, because it also occurred to me that if you made three colours on the three edges, but were able to vary the reconstruction intensity electronically, you could do real-time colour mixing by simply varying the reconstruction beam intensity. I'm now playing with programmable leds to do just that.

As for the student, I've decided that this "edge lit" approach to full colour may be a bit difficult. If you're interested, I have three projects for her:
A computational method for objectively determining the colour of a reconstruction against the colour of the original object. In other words, give me a number, a "figure of merit" for a reconstructed hologram.
A way of getting rid of cross talk in full colour laser transmission holography
Making an image plane full colour reflection hologram from a full colour laser transmission. In other words, an H1/H2 transfer with three lasers.
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