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Thread: Burning ants w/magnifying glass and the like...

  1. #11
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    generally speaking...the lasers are either polarized or not polarized by design to begin with. Most diode lasers we all use are polarized.

    Is this the kind of kit you are talking about

    http://microlaserlabs.com/product_in...60f2e05546f369
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  2. #12
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    Ok so I just had a look at some specifications.. I see things like polarisation ratio of 100:1 I presume this shows its polarised and the 100:1 is the quality of the polarisation?

    Do the PBS cubes accept beams in the same polarisation as far as the Laser modules go and them flip one within the cube thus the two beams leave as a single dual polarised beam?

    Sorry if this is all really dumb questions, I'm totally green to this

  3. #13
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    Quote Originally Posted by madgadget View Post
    Ok so I just had a look at some specifications.. I see things like polarisation ratio of 100:1 I presume this shows its polarised and the 100:1 is the quality of the polarisation?

    Do the PBS cubes accept beams in the same polarisation as far as the Laser modules go and them flip one within the cube thus the two beams leave as a single dual polarised beam?

    Sorry if this is all really dumb questions, I'm totally green to this
    100:1 is the ratio of polarizationishist (i just made that word up, just for fun)

    you didnt read my last post or didnt grasp concept, please re read.

    the beams arent "combined" or "mixed" so to speak...they are only overlapped. One would be vertical and one would be horizontal.
    Pat B

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  4. #14
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    Sorry I did read, my last post I didn't state it clearly but that is what I meant, both beams are mixed in one but at say 90deg apart..

    Does this then limit the amount of beams which you can combine? you couldn't for example make a very good job of combining lots of Lasers using multiple PBS cubes?

  5. #15
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    Quote Originally Posted by madgadget View Post
    Sorry I did read, my last post I didn't state it clearly but that is what I meant, both beams are mixed in one but at say 90deg apart..

    Does this then limit the amount of beams which you can combine? you couldn't for example make a very good job of combining lots of Lasers using multiple PBS cubes?
    you can take a combined set of lasers from a pbs and send it into another pbs but you will loose power...the current train of thought is you can combine two but not 3 or 4 with a PBS...you can...but you dont gain anything.

    NOTEexcluded complex geometries and beam scraping and axicons and fiberoptic splicers for ease of discussion)
    Pat B

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  6. #16
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    Fantastic thanks, its now a lot clearer. However I have another question hahaha... How do people get away with those crazy blocks of diodes all combined into one beam? Are they just in a big random mess of a combined beam using normal mirrors not cubes?

  7. #17
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    Quote Originally Posted by madgadget View Post
    Fantastic thanks, its now a lot clearer. However I have another question hahaha... How do people get away with those crazy blocks of diodes all combined into one beam? Are they just in a big random mess of a combined beam using normal mirrors not cubes?
    yes, sort of
    Pat B

    laserman532 on ebay

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  8. #18
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    I have a dual red, and the way mine works is this.

    i have 2 red diodes, each in a small cylindrical holder called a module (i use an aixiz brand module)

    those modules are placed inside heat sinks and positioned to aim the the proper areas of the PBS.

    if i turn just one on and rotate it inside the heat sink, i will see the output beam go from dim to bright. when its at its brightest point (best to actually measure it with a meter), i tighten a set screw to keep it in that position.

    i do the same thing with the other module.

    here are a couple of very bad pictures of my setup
    http://photonlexicon.com/forums/show...2&postcount=28

    and one i just took..

    When i defocus the beam into a large dot, it makes it easier to find the proper position for the module to be properly polarized.

    Now those big setups im not sure about, but the principle is the same.
    Attached Thumbnails Attached Thumbnails IMG00036.jpg  

    Last edited by keeperx; 05-11-2009 at 09:28.
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  9. #19
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    thos "big random messes" usually use mirrors to collect or aim the beams, but eventually, the ones i have seen pictures, they use a big ol' PBS and collimating optics. just like any other setup. they are just working on a larger scale.
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  10. #20
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    Cool

    Not quite... Those multi-diode setups you see are actually positioning the beams *very* close together so that they make a wider beam. Here's how it works for a 4 laser rig:

    You bounce the beam from the first laser off a mirror so the beam shoots down perpendicular to the other laser. Then you position a second mirror so that the reflected beam from the first mirror *just* passes by the edge of the second mirror, but the beam from the second laser strikes the mirror and is reflected down as well. Now you have TWO beams that are parallel and very close to each other, like this: oo

    Now you do the same thing with another pair of lasers, except that you need to rotate the laser diodes in the mounts by 90 degrees so that the beams are horizontally polarized. (The ones above are vertically polarized.)

    When you send the two pairs of beams into the cube (4 beams total, two into each face), you will get an output beam that still looks like two closely spaced beams, like this: oo But it will have the power of all 4 diodes.(minus some optical losses from the cube and the mirrors of course)

    Some people stack the beams vertically and horizontally before they hit the cube. So you might have a stack that looks like this: 88 (that would be 4 diodes in a 2x2 row) That would be 4 diodes on each side of the cube, for a total of eight diodes. The output beam will still look like a 2x2 stack, but it will have roughly 8 times the power of a single diode.

    The largest one I've ever seen pictures of was an array of 24 diodes (two sets of 4x3 stacks - 12 beams in each stack). The output was a very fat 4 x 3 array which was then passed through a home-made collimator. The output beam was still quite fat, but even with all the losses, a rig like that could reasonably be expected to deliver 3 to 4 watts of power.

    The important thing to remember is that although the PBS cube will allow you to *perfectly* overlap a pair of polarized beams, you can only overlap them once using the cube. Once you do that, you are left with an output beam that is randomly polarized, and this can not be overlapped with more beams of the same wavelength. If you were to send a randomly polarized beam into a PBS cube, half the beam would be rejected at the reflective face inside the cube. Likewise, if you tried to polarize a randomly polarized beam, you would loose half the power.

    The stacking of beams method (sometimes called the knife-edge mirror trick) is used in both commercial projectors (IE: Arctos) and hobbyist projectors. It's a cheap way to get more power than you would otherwise be able to get with just a pair of diodes and a PBS cube. The tradeoff is the larger beam profile, because you can't actually overlap the beams - you can only position them very close together.

    Adam

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