Edge lit DCG

[Jeffrey Weil]

Next time were having a drink together we have to figure out what symposiums we were both at. There must have been a few before Holopack.

It's hard to beat Gunther, he's always a step ahead of everyone else. Irina is very sharp too, she's the pretty blond polymer chemist that works for him.

I actually found a picture of Breakfast attempt. I love the net! http://www.media.mit.edu/spi/Edgelit/edgelit.html I think the later version I saw was full color, and much better. The computer generated image used for the stereogram was a bit different too but it's basically the same image and definitely the same format for the plastic.

Jeff

[Dinesh]

So Ryder got it working. Good for him! He was not happy in Austria.

One of the problems with edge lit is the launching of the light into the medium. We tried it at POC with a bloody huge block of glass butted up against the film and lots and lots of index matching (ug!). Even now, they use a "launch pad" of another material. The problem (one problem, anyway) is that you need to reconstruct with the same "launching glass" and the edge lit is suspended over or next to a large piece of plastic or glass. This devalues the edge lit technique. The beauty of dcg is that I launched the light directly into the glass - there was no need of a block of glass or plastic to launch the light into the medium. The way leds are getting smaller and smaller, it'll soon be possible to almost melt the led into the top of the glass and attach a small battery on the other edge and have a self-contained edge lit hologram with no apparent lighting at all.

[Jeffrey Weil]

Hey Dinesh,

I'm not sure they got it "working" in the industrial sense of the word. I think they got a few good copies but it wasn't reliable. It was a long time ago so I could be remembering it incorrectly.

They were also using the big block of glass. I think it was a wedge shaped piece.

How does DCG give you an edge (pun intended) over silver with respect to the block? Is it that you can come at the film using a more shallow angle requiring a higher resolution recording material?*

Jeff

*remember, I do not speak math as a first language like you do, if you want me to fully understand your answer please keep it simple.

[Dinesh]

*remember, I do not speak math as a first language like you do, if you want me to fully understand your answer please keep it simple.

Well, heck, Jeff, it's because x=3. I thought everyone knew that! Joking! Joking! (but see below*}

Actually, it is because the dcg has a higher spatial frequency, but also because it's a continuous medium, not composed of discrete specks as in silver. Another factor is that you can decide how thick the emulsion is going to be. The issue is:Is edge lit a reflection or a transmission? The light travels along the surface of the emulsion, so you can argue it both ways. However, if it's both ways then do you make the emulsion thin or thick? I argued for thick, made the emulsion fairly thick and got the result you see. Standard , commercial silver has a thickness fixed by the manufacturer and I thought the secret to edge lit was in the thickness of the emulsion.

*Proof of God:
http://everything2.com/title/Monsieur%2 ... ondez%2521

[Martin]

Actually, it is because the dcg has a higher spatial frequency, but also because it's a continuous medium, not composed of discrete specks as in silver. Another factor is that you can decide how thick the emulsion is going to be.

I guess recording layer thickness is the most important part here. AgX emulsions become very difficult to process above a certain level. The thickest holographic emulsions, I've come across, were the Kodak's 649-F plates, which had a 17µm layer back in the 80s. Otherwise, in a non-holographic context, there are nuclear AgX emulsions of 50µm or more. I understand those require quite some special treatment involving very long developing times at a pretty low temperature.

On the other hand, isn't it that processing DCG above 30µm or so becomes increasingly difficult too? So maybe the ultimate recording medium for this might be photopolymers (there are a couple of papers by Phillips where he described the use of Omindex films for edge lit applications).

The issue is:Is edge lit a reflection or a transmission?

Well, from what I read, you can have it both ways: there are edge lit reflection and edge lit transmission holograms. But they rely on different recording geometrics.
Both types so far seem to show some anomalies: the transmission edge lit has less dispersion and with reflection edge lit holograms the most serious issue may be image blurring. In a paper Kubota advocated for 30µm layers in the case of reflection edge lit holograms. By the way, it looks like he even made edge lit R-G-B („color“) holograms.

[Jeffrey Weil]

I think the breakfast attempt I saw was rgb full color, but I've never seen a reflection one of any kind, I bet they are not too bright. Even the transmissions ones I've seen were a little less bright than a conventional hologram.

Jeff

[Jeffrey Weil]

I did remember it incorrectly. The version I saw was a benton style achromatic transmission . B+W

Jeff W

[favalora]

That's cool, Dinesh. I just Tweeted about it (for all of the, like, 9 people who follow me who aren't spambots). Fame! Fame for you!

You, too, can follow me, at @gfavalora .

Achromatic Benton B+W hologram? I have a lot to learn. I'll need to Google around for photos of that.

Regarding edge-lit stuff at the Media Lab. I could have sworn Arno Klein was working on that, too, right? (He was my "host" during my grad school interviews there.) http://asp.cumc.columbia.edu/facdb/prof ... ffil=NYSPI I vaguely recall his being roommates with the co-founder of E-Ink, Barrett Comiskey, still a student at the time. Who knew that he was about to launch a multi-billion dollar industry...

But I digress.

g

[Jeffrey Weil]

Achromatic Benton B+W hologram?

Hello Favalora,

It's a black and white transmission hologram developed by Steven Benton. It's related to a rainbow holograms, sometimes also known as a Benton type hologram.

Its made by producing a horizontal parallax only master and transferring it to the h2 while being tipped at the so called "achromatic angle" This make a b+w hologram with very little chromate dispersion in the vertical axis.

They are beautiful when done correctly.

Jeff Weil

[Dinesh]

Well, from what I read, you can have it both ways: there are edge lit reflection and edge lit transmission holograms. But they rely on different recording geometrics.

Actually, Martin, that's part of the problem. What exactly does "edge lit" mean. 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.

On the other hand, isn't it that processing DCG above 30µm or so becomes increasingly difficult too? So maybe the ultimate recording medium for this might be photopolymers (there are a couple of papers by Phillips where he described the use of Omindex films for edge lit applications).

I've thought of polymers for edge lit. I think there would be a great advantage, if the polymer were uniform throughout the thickness. This is what I meant when I said that dcg was a continuous medium; the index has to be (reasonably) continuous in order to produce evanescent waves. I think that the granularity of silver may prevent evanescent waves inside a silver emulsion.

That's cool, Dinesh. I just Tweeted about it (for all of the, like, 9 people who follow me who aren't spambots). Fame! Fame for you!

You, too, can follow me, at @gfavalora .

Thanks, Favalora! As for tweeting, I'm afraid I have no idea how to do that! I'm afraid I'm the Last of the Luddites. My sister-in-law saw me whip an egg for an omelet with a fork and informed me that there was now a machine for whipping eggs. "Why ?", I asked. Actually, I just discovered texting. It's actually quite interesting, you don't have to indulge in unnecessary conversation. It took me about 3 minutes to text, "I'm at the pub" (the apostrophe threw me, I couldn't figure out how to generate an apostrophe). Now if I could generate equations on the keypad and text those.....

It's a black and white transmission hologram developed by Steven Benton. It's related to a rainbow holograms, sometimes also known as a Benton type hologram.

Well, yes and no. It's one of the problems of holography that there's a surfeit of names and they all get in each others way. The so-called "achromat angle" comes because Benton used the association of the lens equation with Fresnel diffraction. This is a standard method of analysing Fresnel diffraction, but Benton applied it to the slits from an H1. Using this association Benton calculated that the slits are focused at different positions and angles relative to the H1, but they fall along a straight but slanted line. If the H1(s) is similarly slanted with three slits at rgb, then all the slits would superimpose and you'd get true colour.

However, the word "achromat" has also been applied to a hologram made with open aperture in transmission mode. In this mode, the H1 pseudoscopic image is focused onto the H2 plate (as normal), but the H1 is not slitted. If the image is focused at exactly the image plane, there is no dispersion because dispersion is a function of the image point's distance from the image plane. If the image is right at the plane, dispersion is zero. In practice, you can have an image that's about an inch in front and about an inch and a half behind and still get almost no dispersion. You can make it deeper using dispersion compensation, but you have to ask Kaveh abut that!