various questions re image plane reflection

Holomark · Post by **Holomark** » Wed Dec 21, 2011 6:51 pm

Ok, I am trying to make an image plane white light reflection Hologram. I have now created a decent H1 (transmission hologram) which projects onto a white board with 3 inches of image depth. (I will post video of image soon). Actually I made three with exposure times of 30 sec, 1 minute, and 2 minutes. The 30 sec is ok, but not as bright as the 1 minute. The 2 minute is brighter, but has a halo or glowing effect. This 2 minute exposure most closely matches the actual object as the object did appear to have the same halo effect when illuminated.
First questions: should i be concerned with halo from object when shooting H1? If so, I presume methods of reducing would include less light to object, cleaning object (it is very dirty/dusty) Or do I just aim for the exposure time which results in a bright object with minimum amount of halo effect?

Now, since I want to move forward with the next step in in making the white light reflection hologram, should I use the 1 minute exposure or 2 minute exposure? My instinct tells me that I probably want to actually minimize the halo effect so I would want to either use the 1 minute or shoot another at about 90 seconds to maximize brightness and minimize halo effect. Am I correct in assuming that the halo or glow will only cause problems?

Questions related to setup for H2. I believe that I want to keep the expanded and collimated beam that was the reference beam to illuminate the H1 plate. I have therefore kept what was the reference beam and related components the same so that I have the same angles. What about the reference beam for the H2, do I want/need a collimating mirror here also?

I have now placed the H1 in the plate holder - with plate rotated 180 degrees. When illuminated I see an image reflected on a white board. Since the object was about 3 inches deep with different parts of the object at different depths, the image projected on the white board is "in focus" at differnt distances from the H1. Plate holder #2 is now added to the table such that the image projects to both sides of the plate (plate in the middle of image).

Then I started playing with the beam proportions. What I am now comparing is the brighness of the new reference beam in comparison to the brighness of the object - both as seen on the white board placed inthe H2 plate holder. (the reference beam on one side and the object beam on the other side.) I am wondering if I am really seeing all of the object illumination because of the depth of the image. The reference beam is clearly brighter than any one plane of view of the transmitted object, but I wonder if I need to somehow measure the combined intensity of the transmitted object at all depths????

I took a couple of test shots with exposure times of 1 minute, 2 minutes, and 4 minutes. Suffice it to say If I saw a decent white light reflection hologram I wouldn't be writing this long post. What I see: The first thing that jumps out at me is the reflection beam imperfection. Upon a little more inspection I do see what appears to be part of my object, but only on the plate. It almost seems like a cloudiness on the plate in the shape of my object.

There are so many variables I am at somewhat of a loss as to where to start. I want to believe that this is not a movement problem because a) I see some image, and b) the reference beam imperfection on the plate matches that of the beam. Nonetheless I will re-tighten all optical components before my next try. Then what? 1. do I change the beam ratios - more reference, or more object 2. Do I need to adjust polarization (and if so what do I need to buy to do so?) 3. Do I need to expose longer (or shorter)?, or 4. Is there something else I should do???

Misc information that may be helpful.
I am using a 315M (green) laser
plates are VRP
developer is JD-2
coated side of plate is always facing object
developmenregime remains constant

I wil post related photos tonight or tomorrow

holorefugee · Post by **holorefugee** » Sat Dec 24, 2011 2:02 am

The reconstruction beam for the H1 image needs to be the conjugate, so if it was diverging at 15 degrees you need a beam that is converging at 15 degrees. The image should project well onto a piece of frosted glass in the H2 position. The reference for the H2 should be the exact divergence of the reconstruction illumination. So, if you are using a mr 15 bulb then you want the H2 reference beam to diverge at the same rate.

Jeffrey Weil · Post by **Jeffrey Weil** » Sat Dec 24, 2011 11:19 am

Hello Holoref,

You've made a mistake there. You want both beams to be conjugate. The replay on the H1 and the replay on the H2.

If your using a diverging beam to play back the final hologram, like from a mr-16, then you want a converging reference beam when you made it. Not one that matches it's divergence. Now, that's usually not practical so we don't do it often but it's the correct way to do things.

Jeff W

John Sonley · Post by **John Sonley** » Mon Jul 23, 2012 5:16 am

Just found this posting well down the list but thought I'd add my 'pennyworth'

When making my H1 transmission master I always opt for a collimated reference beam and so I need to use a collimated reconstruction beam. As I always use little 50W 12V spotlights to illuminate the finished image plane H2 - the ones I use produce a 15 deg diverging beam, I should use a 15 deg converging H2 reference beam

I tried an experiment with a very 'real' object / H1 master - about 4" deep - I tried a collimated, a diverging and a converging H2 reference beam - and the result ........... not a lot of difference. On a blind test I found it hard to say that one was significantly more like the actual object than another

holomaker · Post by **holomaker** » Mon Jul 23, 2012 9:11 am

Hey guys, my input ???? I’ve found with a good collimated H1(in construction and replay),and as long as the objects not too deep, it doesn’t really effect it so much to worry about now. For projection on image planes try to favor the object to be deeper in the film so the image's central area will be well focused. Let’s see Pictures!

Dinesh · Post by **Dinesh** » Mon Jul 23, 2012 12:12 pm

John Sonley wrote:I tried an experiment with a very 'real' object / H1 master - about 4" deep - I tried a collimated, a diverging and a converging H2 reference beam - and the result ........... not a lot of difference. On a blind test I found it hard to say that one was significantly more like the actual object than another

By and large it doesn't make a lot of difference if you simply look directly at the image, unless the image is very deep. The beam divergence mismatch causes mostly field curvature and distortion, so a very deep image on the H2 will show up distorted front to back. Of course, the eye forgives a lot, so a recognised common object will simply be seen for what it is. For example, if your image is a rocket imagep laned with the nose coming out of the plane, then the divergence mismatch will elongate the rocket in the front a little, but since you expect to see a rocket you'll recognise it for what it is and forgive the small elongation. However, if you were to swing side to side as you look at the object, then you'll notice a difference. The greater the divergence mismatch, the more unreal will be the swing of the front of the rocket. It's even worse for the pseudoscopic view. By the way, if you want a copy of the paper I gave on holographic aberrations, let me know and I'll pass it on.