H2 Copy: Integraf's Suggestion and Yours

[Diode Holographer]

As I mentioned in my intro, I recently made my best transmission hologram yet. I'm really dying to make a hologram with it that can be viewed with white light. I've tried this several times in the past, but I'm having trouble.

Let me start with the "lesson" I have here to work from. "Laser Holography: Experiments You Can Do ...From Edison" A small book which came in the Integraf kit. Here's the lesson in it's entirety.

Figure 5

Assuming you have made a good, bright H1 from Project 2, place it as shown in Figure 5 at the right side, emulsion side away from the laser. The center of the beam should make a 45 degree angle with the hologram. The remainer of the beam that missed H1 now serves as a reference beam for H2, to be located at the left. At this time, place a white card at the location of H2, at a distance approximately equal to the object-to-plate distance of H1. By blocking the reference beam temporarily, a sharp image projected from H1 can be found on the card. Move the card toward or away from H1 to locate the real image. If no image can be found, turn H1 upside-down (emulsion still away from the laser) and try again. Rotate H1 slightly to maximize the brightness of the image on the card.

Actually I can stop right there. My major stopping block right now is getting the real image. I can project an image just fine, but only with a thin collimated beam. I've only just recently managed to get a real image with a diverging beam, but it was only when I shown it through a very small spot on the hologram. The more of the hologram I illuminate the more the image blurs. Similar results with a converging beam and I can't get anything with a wide collimated beam.

So my first major hurtle for getting to the next step in my holography, I need to now why I can't manage to project a real image without anything but a small beam.

[Ed Wesly]

With the H1 illuminated as in the set up as illustrated, first find the usual virtual image reconstruction. Tune it in for the brightest image. Then spin the holo-plate along an axis defined by a vertical line and the real image should be in front of your face!

Another trick with this set up is to move the bright Gaussian center of the beam onto the H1, and use the weaker outer edge of the beam as the reference for the H2. This will lower the ratio for a brighter reconstruction.

This simple technique can give some beautiful achromatic (black & white) results!

[Diode Holographer]

Still no good. I've tried every orientation and I even tried facing the emulsion toward the laser. I can view the virtual image with any type of beam and with any amount of the hologram illuminated, but I can only view the real image when a small portion of the hologram is illuminated. I might also mention that the geometry of their plate placement doesn't work too well for me either. I get the best image when the screen and hologram are not parallel or aligned at the edges. I can get a very sharp real image, just not the way they recommend.

P.S. I'm not sure how I ended up posting this twice, but can a mod delete the other one for me?

[BobH]

By blocking the reference beam temporarily, a sharp image projected from H1 can be found on the card.

This is not true. If you illuminate a transmission hologram with a diverging beam to reconstruct a real image, then place a white card in the image, a sharp cross section will be seen on the card. The image goes fuzzy as its information goes away from the plane defined by the card. As you move the card toward and away from the H1, you'll intersect different cross sections of it. You're probably seeing just what you're supposed to be seeing.

The areas that are sharp on a card in the real image will "burn" into the emulsion when you expose the H2. I always measure the power in the "burns" when setting the beam ratio. Best results come from choosing an H2 recording plane to minimize the "burn" areas and /or exposing to minimize their effects on the final image.

[Diode Holographer]

Wow, that answer sounds like it could be a lot of help. Unfortunately I couldn't understand most of it.

When you say "then place a white card in the image" do you mean place a white card at the position where a real image should be projected? Such as would be the case if I were using a thin collimated beam.

I'm not sure I understand the term cross section in these circumstances.

I'm not sure I follow this line at all. "The image goes fuzzy as its information goes away from the plane defined by the card." If you mean the real image sharpens and blurs as you vary the distance between the card and the H1, then yes but still with all the stipulations previously stated.

The areas that are sharp on a card in the real image will "burn" into the emulsion when you expose the H2. I always measure the power in the "burns" when setting the beam ratio. Best results come from choosing an H2 recording plane to minimize the "burn" areas and /or exposing to minimize their effects on the final image.

I'm not sure either of us is understanding the other. I can't get anything that would be called "sharp". I can't get any real image at all unless a very small portion of the hologram is transmitted through. I've also noticed something else. The only time I can get a real image with a converging or diverging beam is when the degree of convergence or divergence is small. The small the degree, the sharper the image. I can project an image with a thin collimated beam, then when I start to slowly spread the beam, the image starts to blur. It soon blurs beyond recognition.

I hope I don't seem like a total moron. I'm sure its something simple that I'm just not catching. Also, don't think I just come up with this out of the blue. I've put hours into trying to project and image as suggested by integraf and others. I've read ever page in the Beginer Holography forum here, I've searched through HoloWiki and I've looked through several other individual sites. Speaking of HoloWiki, how does one access the K-12 page that sounds so interesting?

[BobH]

Let's say the image is a human head looking toward the H1. When you project the real image with an undiverged raw laser beam, you see a sharp image of the face on a card. AS the card is moved closer to the H1, the face image gets smaller. As the card is moved away from the H1, the face image gets bigger. With an undiverged raw beam on the H1, there is always a sharp image of the face on the card regardless of its distance from the H1.

Now illuminate the H1 with a beam diverging from a point a long way away (that is, as collimated as you can make it). Start by placing the white card very close to the H1. You should see a blob of light. As you move the card away from the H1, eventually you'll see the tip of the nose come into focus. As you continue to move the card away from the H1, the cheeks will come into focus on the card and the tip of the nose will blur out. Continue to move the card back and the eyes, then the ears will focus as you pass them but the rest of the three dimensional image will blurr out because it's focused at different locations in space.

[Diode Holographer]

With the H1 illuminated as in the set up as illustrated, first find the usual virtual image reconstruction. Tune it in for the brightest image. Then spin the holo-plate along an axis defined by a vertical line and the real image should be in front of your face!

Let me be sure I understand you as well, Ed.

If figure 1 is me viewing the virtual image, then I should be able to simply turn the hologram clockwise about 90 degrees and the real image will appear in the position of the white card, all as in figure 2. Is that right?

Another trick with this set up is to move the bright Gaussian center of the beam onto the H1, and use the weaker outer edge of the beam as the reference for the H2. This will lower the ratio for a brighter reconstruction.

That is the suggestion they are making in the book, but as of yet I have not been able to project the real image as they describe.

This simple technique can give some beautiful achromatic (black & white) results!

That's what I hear. That's why I'm dying to figure what I'm doing wrong. I really want to make a deep hologram that's white light viewable.

[JohnFP]

A real quick summary of what others have stated already.

Your image WILL be fuzzy if illuminating the whole plate. Just shoot and be surprised!

[BobH]

In your figure 1 on the left side, you are looking at the virtual image. If you rotate the plate 180 degrees and don't move your head, you'll see the real image.

If your set-up is anything like the drawing, the real image will be terribly distorted. It's because the reference beam is diverging rapidly when you make the H1. If you then rotate the plate 180 degrees to see the real image, the reconstruction beam is then also diverging (instead of converging, which would match the reference beam used for recording it). That's why people use collimated beams for whenever they plan on reconstructing a real image. You want to always match the reconstruction beam to the recording reference beam geometry as well as you can for best results. 8)

[Diode Holographer]

Let's say the image is a human head looking toward the H1. When you project the real image with an undiverged raw laser beam, you see a sharp image of the face on a card. AS the card is moved closer to the H1, the face image gets smaller. As the card is moved away from the H1, the face image gets bigger. With an undiverged raw beam on the H1, there is always a sharp image of the face on the card regardless of its distance from the H1.

Incorrect. Perhaps this is the way it should be, but it is not what is happening. The further from the plate I take the card the larger the image gets AND the more it blurs. I does not remain sharp at varying sizes.

Now illuminate the H1 with a beam diverging from a point a long way away (that is, as collimated as you can make it). Start by placing the white card very close to the H1. You should see a blob of light. As you move the card away from the H1, eventually you'll see the tip of the nose come into focus. As you continue to move the card away from the H1, the cheeks will come into focus on the card and the tip of the nose will blur out. Continue to move the card back and the eyes, then the ears will focus as you pass them but the rest of the three dimensional image will blurr out because it's focused at different locations in space.

So the degree of divergence in the beam is a factor.

Just to be sure I am really using the real image. If you look back at the last 2 figures, both of these are acurate recreations of both my viewing of the virtual (left) and real (right) images (except that the virtual image would be projected with a "raw" beam) and my set-up for shooting an H2. It only take a 90 degree turn from viewing the virtual image on the left to projecting the real image on the right. Do I have the real image? Where am I missing the 180 degree spin?