Edge lit DCG

Present your work.
Jeffrey Weil

Edge lit DCG

Post by Jeffrey Weil »

Hey Dinesh,

Don't even try to fix the terminology, it's a total mess. Just dealing with the word "stereogram" could start a thread that goes on forever and destroys civilization as we know it.

Now you want to rename the achromatic angle, that term has been published too many times to go back now.

It's an impossible battle, fixing holographic terminology. It's like PC vs. Apple, or who invented dot matrix holography first. I say just make cool images and enjoy life.

Are you and Joy going to be in the lab after Holopack? I'd like to take you up on your offer to see your place.

Jeff
Martin

Edge lit DCG

Post by Martin »

Dinesh wrote:True edge lit holograms would require that the reference is an evanescent wave. However, such a reference is neither reflection nor transmission. People have used very (very!) steep angles in both geometries and called it "edge lit" but then one requires large prisms or blocks of glass. I reasoned that if it could be possible to generate an evanescent wave along the surface of the emulsion, then blocks of glass or large prisms would not be necessary. But, it's very difficult to produce an evanescent wave, you have to hit the back end of the emulsion at ju-u-st the total internal reflection angle. So, I reasoned that if the emulsion were thicker than would be found in commercial silver, I'd have a better chance.
I see. Speaking of evanescent waves, I remember being struck by the discrepancy that some people used extremely thin recording materials (e.g Sainov) whereas others (Phillips) did use quite thick photopolymers.
BobH
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Edge lit DCG

Post by BobH »

Digilens was making evanescent wave HOEs in 2002 for a telecom application. Our electrically switchable hologram material with a chirped grating was in contact with a waveguide, essentially a switchable cladding, and used as a dynamic gain equalizer. It worked but couldn't be kept in calibration. Only cost forty million, as the telecom industry was crashing down around us. Now I'm making edgelit HOEs for other applications. The current ones are recorded in UV and used in IR. Biggest problem now is ITO reflectivity at high angles of incidence!
Dinesh

Edge lit DCG

Post by Dinesh »

BobH wrote: Only cost forty million,
Forty million, huh? Ours cost about 10 bucks (and a pound of hamburger meat...no, I'm joking!). By the way, before you blow a gasket, I realise that yours is a lot more sophisticated than ours! I had no specific end in mind, just an idle thought "Can you launch an evanescent wave into a dcg emulsion. If so, you don't need large launching glass and index matching (Ug!)"
BobH wrote: Biggest problem now is ITO reflectivity at high angles of incidence!
You might want to talk to Steve Smith. I threw him out an idea at San Fransisco that had to do with ITO's and it may be that you're also working along those lines.
Martin wrote: I remember being struck by the discrepancy that some people used extremely thin recording materials (e.g Sainov) whereas others (Phillips) did use quite thick photopolymers.
Strictly speaking, the evanescent wave needs only a few wavelength, so a micron or two should be enough. However, in order to launch, or create, an evanescent wave you need to match to the specific index. It may be that whether it needs a thick or thin emulsion depends on the index.
Jeffrey Weil wrote:Are you and Joy going to be in the lab after Holopack? I'd like to take you up on your offer to see your place.
We may actually be there this year, since Vegas is just around the corner for us. However, whether we're there or not, we'll be back here afterwards. So, certainly come over.
Martin

Edge lit DCG

Post by Martin »

Dinesh wrote:Strictly speaking, the evanescent wave needs only a few wavelength, so a micron or two should be enough.
Apparently, it can be even much thinner - 8nm thickness only in this case: http://www.physik.tu-berlin.de/institut ... sainov.pdf
However, in order to launch, or create, an evanescent wave you need to match to the specific index. It may be that whether it needs a thick or thin emulsion depends on the index.
OK, thanks.
Dinesh

Edge lit DCG

Post by Dinesh »

Martin
Thanks for the paper. I noticed a couple of things. From his equation 2 for the penetration depth, z_0

z_0 = lambda_0/(2pi(n^2*sin^2(phi) - 1)(^0.5))

that z_0 is inversely proportional to the index. Thus, the larger the index, the smaller the penetration depth. This may explain the difference you noted.

Also, he uses a prism to launch the light. It may be that to achieve the proper TIR for these high indices, you need a prism, but then, to me anyway, the advantage of edge lit is lost. For me, the beauty of edge lit is its simplicity. If you need a prism to reconstruct, I think simplicity is lost. However, to launch without a prism may need thicker emulsions and that may also be a source of the disparity between thin and thick emulsions for edge lit.
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