newbie question re: beam expander

[favalora]

Hi -

I am a bit ashamed to ask this, but: is there a well-known inexpensive supplier of beam expanders (or "unintentional beam expanders")?

I have an old HeNe and would like to use it to illuminate a transmission hologram that I made about 10 years ago in a holography lab at MIT. Is the general wisdom to just find a microscope objective and use that? Or an eBay seller who has something equivalent? I'm wondering if there's a $20 solution.

Best,
Gregg

[MilanKarakas]

Hi -

I am a bit ashamed to ask this, but: is there a well-known inexpensive supplier of beam expanders (or "unintentional beam expanders")?

I have an old HeNe and would like to use it to illuminate a transmission hologram that I made about 10 years ago in a holography lab at MIT. Is the general wisdom to just find a microscope objective and use that? Or an eBay seller who has something equivalent? I'm wondering if there's a $20 solution.

Best,
Gregg

Hello, Gregg.

There are mainly four ways how to see your transmission hologram. Firs one is the simplest; just shine laser spot onto white surface and hold hologram in front of it - you should to see pretty clear hologram. Just need to find proper angle from where is such hologram recorded.

Another two ways is to use positive or negative lenses (both lenses serving to expand or diverge beam). Even the worst quality lenses will gives you chance to see the hologram (as long as you not transfer it to H2, or copy). If beam is diverged too quickly, object(s) o the hologram may appear smaller. But, if you want to see it in the right proportions as it is recorded (original dimensions of the object, so to speak), then it will be good that expanded beam is collimated, or at least looked from great distance.

And fourth, and my favorite way is to project 2D image onto screen; shine laser from the opposite side from where it is recorded, and image should be projected on the screen. Depending where you illuminate this hologram, projected image will be from as is seen from this perspective (object will change shape). You may notice that some part of the object is sharp, other part is blur and with noise; the sharpest part will be one where object was during recording. For example, if object was 10 cm from the plate, projected image will be sharp there, at 10 cm from the holographic plate to the screen.

Also, you may decide to see hologram with other wavelength than hologram is recorded. Then whole scene will be somewhat shifted (having different angle of view). So, red, green, blue... no mater which laser pointer you chose, you will see the image clearly. Only white light (or three lasers combined) will confuses you - you will see object as a rainbow (or three separate objects in case of RGB combined lasers, each object at slightly different position, and color).

I hope this helps.

Best--
milan
---

[lobaz]

Hi,
if you just want to illuminate a transmission hologram, I would not go into HeNe at all. In my small gallery of holograms I illuminate transmission H1's with a cheap 1-5 mW laser diode without the collimating optics, such as this: http://www.gme.cz/dokumentace/758/758-0 ... -008.1.pdf.
The collimating optics can be easily unmounted with pliers. Such diodes cost about 5 USD. I am quite sure you will not find any beam expander under 5 USD Moreover, such a diode without collimating optics is very safe.

Petr

[Dinesh]

Depending on the depth of the image, an led would work. It reconstructs images at up to about 5 in reasonably well. You could also try a fast negative lens.

[favalora]

Ah, thank you for the clever suggestions. [I had checked "notify me when a reply is posted" but those notifications seem not to have arrived]

I'll see if I can make some of these ideas work... I have quite a few red LEDs at home, the kids like to experiment with them. Somehow I lack any diverging lenses... And I never would have thought of the white paper trick.


gregg

[Dinesh]

And fourth, and my favorite way is to project 2D image onto screen; shine laser from the opposite side from where it is recorded, and image should be projected on the screen. Depending where you illuminate this hologram, projected image will be from as is seen from this perspective (object will change shape). You may notice that some part of the object is sharp, other part is blur and with noise; the sharpest part will be one where object was during recording. For example, if object was 10 cm from the plate, projected image will be sharp there, at 10 cm from the holographic plate to the screen.

It depends on how thin your laser beam is. If the beam is a raw beam (no expansion) then the image will be 2D and sharply in focus, no matter how far the screen is. But, as the screen gets further and further away, the 2D image size increases. As the laser beam diameter increase, the 3D fills in and the image becomes more and more localised in space as a 3D image. This is because any point (or very small area) on the plate (or film) has only the 2D information about the image from a particular perspective. The entire hologram is a conglomerate of many thousands of 2D views from several perspectives. If you illuminate a larger area, you integrate several 2D images into 3D.

[holomaker]

why not use a decent concave mirror? i do it all the time ................

[Dinesh]

Gregg,
Quickie thought I thought I'd jut down. If your son plays with marbles, a marble makes quite a good ball lens. This is quite good for rapid expansion.

[favalora]

I tried a bright LED last night and the transmission hologram was visible. Thanks for the idea!

g