Some sort of diffraction grating?

Hey guys,

I am looking for a "diffraction grating" (not sure if this is the name of the optic), that projects something like this when you shine a laser through it:

O O O O O O O O O O O O O O

The little green O's are the dots. I know that common diffraction gratings make a line or matrix of laser-light (as I own a couple), but I would need an optic that can do this

O O O O O O O O O O O O O O

instead of this

________________________________________

Any help is greatly appreciated.

Thanks

-Jakob

P.S. I remember finding a tiny little acrylic cylinder inside of a KES-400A BluRay drive that did this, but the dots were pretty bad quality, and were concentrated in the center (bright in the middle, and getting dimmer and dimmer as they went towards the ousides). It would be great if I could find a better quality one than that.

pianoman2011 said:

Hey guys,

I am looking for a "diffraction grating" (not sure if this is the name of the optic)

Click to expand...

Correct.

I personally haven't seen any diffraction gratings that just give a line of dots, but i suppose it's pussible, they usually give you a matrix-like shape of dots, like so:
,
although, I don't know why there's a red line in the middle.

Yes the kind of optic I am talking about is like that but just displays one row of dots instead of the 5 that one shows. Thanks for the quick response. But would anybody know where to buy this??

-Jakob

You might find one from Fred at SurplusShed- Search - Surplus Shed or search ebay-GL--Len

They are called "Beam fan" diffraction gratings at Dragon Lasers and they produce a line of dots, rather than a grid of dots.

First of all, you need to start with a gaussian beam profile. So you'll want to use a low divergence gas laser, unless you have some nice optics to work with if you prefer LDs.

To make the "o" ring diffraction pattern, you must polarize the light beam by "twisting" it around it's axis of intensity. You're looking to make something called an optical vortex. They require some precision equipment for effective results.

If you have a high resolution laser printer, you can print the simple "fork" shape needed, in a small font, on an overhead transparency.

Optical vortex - Wikipedia, the free encyclopedia

Modulated optical vortices

http://laser.physics.sunysb.edu/~amol/papers/siemens/siemens.pdf

http://www.compadre.org/advlabs/tcal/files/PadgettM4.pdf

I haven't made one myself, but next week, I'm joining a research team at the department to experiment with them.

To get multiple of them in a line. I would first use a regular high- line density grating to split the beam. Then, I would block off all the rows except one- leaving me with a row of gaussian dots. I would then place a "fork" grating in the profile of each beam. This should leave you with doughnut like rings in a row. You can't spin the beam's polarization, and THEN split it into a row of many, the rings would diffract differently than how a gaussian beam would.

I hope this helps a bit, I'll try and do some digging and see if I can't find a picture of the fork grating for you.

-Tyler

EDIT: Just realized you were actually talking about dots, not rings or "o"s.

As a side note, I have experimented and found optics in at least 3 sleds that do a row of dots. I know for certain there is such an optic in the KES-400A sled (ps3) as it was the first sled I messed around with. I have also experimented with the LG 8x Bd-r sled. as well as lpc-815 and ggw sleds. I am not certain which of the last 3 had for certain. I wouldn't be surprised if most if not all sleds have an optic that does what you are asking. My suggestion, if you have any sleds kicking around, then experiment. I'm not quite certain where the optic piece is located in the sleds either, as it wasn't until things were disassembled that I was playing around and noticed the pattern. It's a flat rectangular transparent wafer, with some sort of coating though. I wish I could be more specific, sorry.

@hakzaw: thanks for the links, but there were only some normal line and matrix diffraction gratings at the surplus shed.

@ash: thank you SO much! a name of this diffraction grating is exactly what I was looking for.

@meatball: yeah I was talking about dots, but thanks for all those links. a laser vortex sounds really cool and those should provide me with some fun reading.

@stridast: wow thats cool... I had no idea that they were also in the 8x and LPC sleds... I never experimented with the optics from those, only from the KES-400A... thanks for telling me about this, I'll definitely experiment around with some sleds when I get some.

-Jakob

only downside is the dots are spaced about the same as in the KES sled. But then, every diffraction grating is much brighter in the center, getting progressively dimmer the farther out you go. It's just a matter of if it works for your purposes or not.

pianoman2011;662521 said:

@ash: thank you SO much! a name of this diffraction grating is exactly what I was looking for.

-Jakob

Click to expand...

Oh. I forgot to say: You can also get this pattern (beam fan) from reflecting a laser off of a CD.
Remeber to wear your safety goggles when you try it out.

@stridast: I looked at some of the pictures of beam-fan gratings on CNI and Dragonlasers and even though still seemed brighter in the middle, they were far better than the bean-fan grating from the KES-400A. I remember the KES had like 4 really bright beams and the rest were dim as hell. It's a lot better looking with the ones from CNI and Dragonlasers.

@ash: I always you protection! I have safety goggles rated for all the wavelengths I own and thanks for the CD tip, but unfortunately I'm going to need much higher-quality beams for what I'm working on. Plus, I'd much rather prefer a transmission grating instead of a reflection grating

-Jakob

One stop laser shop sells plastic transmission grating at low cost, and is hobbyist friendly...

Not only that, Amanda can mail it to you...

Steve

@lsrfaq: Manufacture and developer of laser light show hardware and software.

Is that that website you're talking about? Cause if so, I searched their optics section and all they seem to sell is Front Surface Mirrors, Dichros, and Beam Splitters... No transmission gratings.

-Jakob

A cheap alternative, in my physics class we had a piece of equipment that could make a really small hole, if you shined a laser through it you would then get a fan diffraction, but it won't the crisp and defined dots that you would get from a purpose built grating.

I found using a metal caliper, and making the gap really small shining your laser through it you can make a pretty cool pattern.

you ideally need the hole to be a similar size to the wavelength, so it's easier to do this with red.

@asherz: Unfortunately all of the beams have to be fairly high-quality so this wouldn't work. But thanks for the info, sound like fun to play around with.

@bobh: Thank you so much for this! I have started researching DOEs and they seem to be PERFECT for the application. Could you maybe direct me to a website that would give some free samples? I haven't found any that do that yet. Again, thank you!

-Jakob

pianoman2011 said:

@lsrfaq: Manufacture and developer of laser light show hardware and software.

Is that that website you're talking about? Cause if so, I searched their optics section and all they seem to sell is Front Surface Mirrors, Dichros, and Beam Splitters... No transmission gratings.

-Jakob

Click to expand...

This New thing, called phone.. Not everything is on the WWW. Trust me, they stock it... Call Amanda..
Edmund Industrial Optics and Thorlabs stock DOEs, but prepare to die of sticker shock...

If you need a DOE made, for commercial purposes, Peter Meyer is one of the best in the world:

http://www.creativelaser.de/hardware/grating_page_frame/grating_page_frame.htm

I've done them, but I had a etalon stabilized , single mode UV argon at my disposal. You can get by with something like a JDSU microlaser or a coherent compass, and really good holo film.. If your into "C" programming, there is a PDF out there with code for rendering a master with a laser printer, but then you need to focus it down and have a really good mastering laser..


Steve