Diffraction gratings

[The_Stranger]

Short question, what are they (diffraction gratings) and what are they used for? Dave was so kind to include some with the laser he sold me, but apart from a groovy effect they produce when looking through them at a candle or even better, a TV, what do they do? When I shine a laserbeam at them, they produce a couple of copies of that beam, in a 3 by 3 pattern.
The holowiki is rather empty about the gratings and other HOE's:
http://holowiki.com/index.php/Holograph ... l_Elements

And speaking of that laser, on the lasertube, a 1145p, there is a marking indicating the plane of polarisation. It is indicated by an arrow, but it is pointing along the tube itself, something like this:

Code: Select all

__________
       PoP|
      <-->|
__________|

I would have expected an up/down arrow, but what does this tell me about the plane of polarisation?

[BobH]

Regarding the polarization, if you draw a line on the front face of the laser that goes through the output aperture and in an orientation that hits where that arrow is, that will be the polarization direction of the laser beam.

[The_Stranger]

Regarding the polarization, if you draw a line on the front face of the laser that goes through the output aperture and in an orientation that hits where that arrow is, that will be the polarization direction of the laser beam.

So if we take the rough "sketch" in my first post, the polarisation "waves" would be coming and going away from us?

pol.jpg (9.67 KiB) Viewed 3394 times

[BobH]

Yes, that's how I've seen it.

[dave battin]

Short question, what are they (diffraction gratings) and what are they used for? Dave was so kind to include some with the laser he sold me, but apart from a groovy effect they produce when looking through them at a candle or even better, a TV, what do they do?

yes i included this grating to use in your holography set ups to illuminate your objects. i like to use fine frosted glass to light my subjects, but if i only use one raw beam hitting the frosted glass i get a very "grainy" look, but if i introduce the diffraction grating an inch or two before the frosted glass you will now have a few raw beams hitting the frosted glass and get a nicely lit object and all the grainy look is gone. These grating can be used to do many things, The late great Rudie Burkhout used HOES on quite a few of his holograms, for instance the "12 MW boogie" i believe he used the gratings to multiply his images. Check this link for a good read of Rudie's magic holograms ..........

http://rudieberkhout.home.mindspring.co ... ograms.htm

[Joe Farina]

i like to use fine frosted glass to light my subjects, but if i only use one raw beam hitting the frosted glass i get a very "grainy" look, but if i introduce the diffraction grating an inch or two before the frosted glass you will now have a few raw beams hitting the frosted glass and get a nicely lit object and all the grainy look is gone.

Nice tip, thanks Dave. I printed a hard copy for my files

[The_Stranger]

Short question, what are they (diffraction gratings) and what are they used for? Dave was so kind to include some with the laser he sold me, but apart from a groovy effect they produce when looking through them at a candle or even better, a TV, what do they do?

yes i included this grating to use in your holography set ups to illuminate your objects. i like to use fine frosted glass to light my subjects, but if i only use one raw beam hitting the frosted glass i get a very "grainy" look, but if i introduce the diffraction grating an inch or two before the frosted glass you will now have a few raw beams hitting the frosted glass and get a nicely lit object and all the grainy look is gone. These grating can be used to do many things, The late great Rudie Burkhout used HOES on quite a few of his holograms, for instance the "12 MW boogie" i believe he used the gratings to multiply his images. Check this link for a good read of Rudie's magic holograms ..........

http://rudieberkhout.home.mindspring.co ... ograms.htm

So, do I understand it correctly you use a beam, without any lenses, shine it on the grating and let the resulting multiple beams hit a piece of frosted glass and use the light from that to illuminate the object? (and use a beamsplitter plus lens to create the reference beam?)

Something like this picture? (disregard pathlengths etc)

Untitled.jpg (18 KiB) Viewed 3079 times

Does the frosted glass need some special specifications, I assume like the thinner the better, or doesn't it really matter?

That piece of Rudie is interesting, but without some more experience a bit hard to imagine and understand, so I will save that for later, when I can do basic 1 and 2 beam holograms consistently. It does make some really nice holograms though...

[Joe Farina]

That looks like it. Dave's tip is a really good one, I think. The thickness of the diffusing glass shouldn't matter.

I sandblast my own diffusers using 600 grit silicon carbide (which is cheaply available on eBay), although I do have a full sandblasting setup. But this could also be done using inexpensive equipment, like the Paasche Air Eraser. That way, any level of diffusion can be made, from mild to strong. It might be beneficial to have an AR coating on the smooth side of the glass, using the inexpensive windows available from Edmund: http://www.edmundoptics.com/onlinecatal ... uctID=1919

[Danny Bee]

That looks like it. Dave's tip is a really good one, I think. The thickness of the diffusing glass shouldn't matter.

I sandblast my own diffusers using 600 grit silicon carbide (which is cheaply available on eBay), although I do have a full sandblasting setup. But this could also be done using inexpensive equipment, like the Paasche Air Eraser. That way, any level of diffusion can be made, from mild to strong. It might be beneficial to have an AR coating on the smooth side of the glass, using the inexpensive windows available from Edmund: http://www.edmundoptics.com/onlinecatal ... uctID=1919

heres a tip is to frost or etch both sides of the glass, or 2 thin ground glasses with a thin spacer in between the glass (this sometimes give better control over the diffusion of the light). This is what I use to simulate studio lighting in holography

[dave battin]

yes, you have it correct above, this method works very well for doing rear-lit screen situations, and i like the double sided frosting idea, when i use the single sided frosted glass i make the laser hit the frosted side first, as i think it may be more efficient this way :think: :