Iridescence recording ?

[Ed Wesly]

Duh, yeah, Gentet did butterflies.

It’s amazing what a little walk will do to start the gray matter hard drive memory banks! I haven’t had a chance to look at all the links above, but if you have, you might have seen the interesting stacked grating structure of the Morpho Butterfly wing. This profile was the basis for a very interesting optical set up to make similar structures holographically.

James Cowan of Polaroid Corp (back in the day, for sure!) used three beams to make an interesting grating in photo-resist. Two beams were incident on one side of a photo-resist plate without anti-halation to make a grating, resulting in the usual parallel lines, while a third was incident along the normal from the other side. This one then made fringes with the other two that were reflection like fringes, more or less parallel to the substrate.

Photo-resist develops by removing material in the bright fringes, and in this beam configuration the resulting fringe structure looked sort of like the butterfly wing structure. Cowan called it an “Aztec” structure, definitely more apropos, as there was definitely a stepped cross-section, with the tip of the pyramid toward the air and the broad base at the bottom of the glass.

I remember seeing an embossed hologram of a coin he had done in this fashion and it was pretty much black and white. So if you are interested in this technology, look up James Cowan, Polaroid, Aztec grating, ca. late ‘80’s early ‘90’s. He was always showing the hologram and some butterfly wings at the Photnics conferences, maybe even when they were still in LA.

Again, whatever happened to this technology? The idea was that you could make a sort of reflection hologram that could be replicated by embossing.
I might be a fuzzy on some of the details, but that’s all I know for now.

[Martin]

James Cowan of Polaroid Corp (back in the day, for sure!) used three beams to make an interesting grating in photo-resist. Two beams were incident on one side of a photo-resist plate without anti-halation to make a grating, resulting in the usual parallel lines, while a third was incident along the normal from the other side. This one then made fringes with the other two that were reflection like fringes, more or less parallel to the substrate.

Photo-resist develops by removing material in the bright fringes, and in this beam configuration the resulting fringe structure looked sort of like the butterfly wing structure. Cowan called it an “Aztec” structure, definitely more apropos, as there was definitely a stepped cross-section, with the tip of the pyramid toward the air and the broad base at the bottom of the glass.

I remember seeing an embossed hologram of a coin he had done in this fashion and it was pretty much black and white. So if you are interested in this technology, look up James Cowan, Polaroid, Aztec grating, ca. late ‘80’s early ‘90’s. He was always showing the hologram and some butterfly wings at the Photnics conferences, maybe even when they were still in LA.

Again, whatever happened to this technology? The idea was that you could make a sort of reflection hologram that could be replicated by embossing.
I might be a fuzzy on some of the details, but that’s all I know for now.

I remember Cowan's honeycomb microlens. I run into (I guess in the 80s) it when I became interested in Lippmann's integral photography.

[Sergio]

Ed, I remember saw something about Aztec grating on the world of security holograms, some new security item i guess.

[Ed Wesly]

Hopefully Cowan is getting his due, but knowing how sleazy the security hologram companies are they're probably doing it because his patent ran out.

He was a clever guy, (and hopefully still is if he's in good health), as evidenced by the other three beam recording scheme mentioned above by Martin. Jim's set up used three point sources like at the corners of an equilateral triangle, all aimed at the photo-resist plate from the same side. The interference pattern was sort of triangular, and yielded wells at the nodes, which could be used as molds for lenses like Martin mentioned for full=parallax integral photographs, or little reservoirs or cups for something, and since he worked for Polaroid I guess it might have been for minute amounts of developing goo.

Now that I think of it, Cowan was active morel like in the early to mid-80's! Thanks for the memory jog!

It would be so nice to have all the time and money to try some of the set ups which were discussed here, holographing insect wings, 3 beam interference...

[holo_cyware]

Ok, I just put a Morpho butterfly under a spread green laser, and it looks "metalic", but obviously green. Due to the speckle is not clear what it'll look like, but I'll post the results.
Also, the nice effect from the iridiscence comes from the reachness of colors/hues. In the morpho's case, there are all kinds of blues, and at the slightest angle change the color hues sudenly shift, on a scale level thus the "metalic" appearance. Now, in the case of 520nm illumination the hues are no longer there, but the intensities are, so a impressive hologram may still be possible.

Now I'm convinced one needs a RGB system to get the colors right in the case of interference. And I just remembered Gented used something like 2 different blue lasers to get the colors right. It's not just a matter of mixing up three fundamental frequencies after all to get full color.

[favalora]

I'm late to the party here, but doesn't the Iridigm / Qualcomm "imod" display function using electronically modulated iridescence?

http://www.opticsforkids.com/celebs/MilesMark.html
http://www.laserfocusworld.com/articles/279829

g

[JohnFP]

I wonder if a couple of few shots at different angles may achieve a somewhat similar effect to the shimmer?