Why why why would a transmission holo only replay when wet!?

Justin W · Post by **Justin W** » Thu Jun 11, 2009 3:19 am

Kaveh wrote:I was hoping to create a little animation to show the effect. I will try to do that.

Kaveh - thank you for your reply. It makes perfect sense that fringes recorded in a swollen emulsion will be properly oriented for replay only when said emulsion is again swollen to the same degree, but I still look forward - as I am a very visual learner - to viewing any visuals you would be willing to create and post. Loosely understanding this on a broad conceptual level will be nowhere near as valuable as seeing these physics laid out technically and specifically, and I thank you for being willing to aid myself and others in visualizing what's occurring here!

As far as index-matching with water is concerned: this was an experiment in simplifying darkroom work, and one that I'm glad only consumed a few scrap strips of film. I guess if index-matching was as simple as using good ol' H2O, then this would be by now a commonplace thing

Oh, well... That's holography as I know it; First learn 1000 ways to do it wrong, then land on one or maybe two ways to do it right

Kaveh · Post by **Kaveh** » Thu Jun 11, 2009 3:41 am

Justin W wrote:Kaveh - thank you for your reply. It makes perfect sense that fringes recorded in a swollen emulsion will be properly oriented for replay only when said emulsion is again swollen to the same degree, but I still look forward - as I am a very visual learner - to viewing any visuals you would be willing to create and post.

Justin, I think humans are naturally "visual" learners, but have had to learn by reading text as it has been the only way to communicate information in detail. Now that we can use multimedia easily we should use it more and more...

I have been wanting to do some online multimedia recordings to put across my understanding of holography, and I thank you for giving me the reason for doing the first one.

OK, I have done the visuals, and just need to put some audio. Then upload from a bad line in Iran in the middle of election fever, with rumours that they will cut internet tomorrow while election goes on. So must do today, haha.

Oh, well... That's holography as I know it; First learn 1000 ways to do it wrong, then land on one or maybe two ways to do it right

The important thing is that you have not just thrown the test holos in the bin and forgotten about it, but are determined to understand what happened and why it is not working... That is how you learn a trade well.

Ed Wesly · Post by **Ed Wesly** » Thu Jun 11, 2009 12:16 pm

Here's a visual to help see the problem. Think of the fringes being like Venetian Blinds across the holographic plate. With your geometry, the blinds are tilted at about 30 degrees from the normal. This is their orientation while wet, but when the emulsion dries and shrinks, they collapse and close the fringe/blinds so much that no light can sneak in-between them!

Justin W · Post by **Justin W** » Fri Jun 12, 2009 2:53 am

Nice, Ed!
I can dig it and grok it.
I'm hoping Kaveh's multimedia creation helps explain how it is that a beam hitting the emulsion at 56.6 degrees results in baffles cut through at 30 degrees.
Clearly it's an interference thing, but I just can't picture it...
I wish I could shrink down to the size of an atom and watch it happen for myself :dance:

Kaveh · Post by **Kaveh** » Fri Jun 12, 2009 3:02 am

Ed Wesly wrote:Here's a visual to help see the problem. Think of the fringes being like Venetian Blinds across the holographic plate. With your geometry, the blinds are tilted at about 30 degrees from the normal. This is their orientation while wet, but when the emulsion dries and shrinks, they collapse and close the fringe/blinds so much that no light can sneak in-between them!

Ed, I don't think that is the right analogy, because it gives the impression that light has to pass through the louvers whereas it has to hit it as the right bragg angle or near. Hope my little graphic will be up soon. I am preparing in Iran, my colleague in India needs to upload it, and you infidels in America will view it.

(Just a joke, in case there is confusion!!)

Kaveh · Post by **Kaveh** » Fri Jun 12, 2009 7:01 am

Here is my explanation in multimedia:

http://holographer.org/recording-a-holo ... -emulsion/

dave battin · Post by **dave battin** » Fri Jun 12, 2009 8:40 am

nice job Kaveh! thank you for this explanation,its much more clear now!

Justin W · Post by **Justin W** » Fri Jun 12, 2009 6:12 pm

Fantastic, Kaveh!
Thank you, brother. That was an excellent presentation that really painted the picture of the tiny happenings inside the emulsion.

Do I correctly glean from what I watched that the fringe angle is the average of the object beam angle (generally normal) and the reference beam angle?

Kaveh · Post by **Kaveh** » Fri Jun 12, 2009 6:35 pm

Justin W wrote:Fantastic, Kaveh!
Thank you, brother. That was an excellent presentation that really painted the picture of the tiny happenings inside the emulsion.

Do I correctly glean from what I watched that the fringe angle is the average of the object beam angle (generally normal) and the reference beam angle?

Correct, the bisector of the angles inside the emulsion. Peace to you brother.

DJ Mathson · Post by **DJ Mathson** » Fri Jun 12, 2009 7:33 pm

Excellent presentation, Kaveh.