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Thread: PBS CUBES

  1. #1
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    Default PBS CUBES

    I've been struggling for a week trying to optimize the combined throughput when beam combining with a PBS. With 445 diodes oriented so that their near field patterns looks like === and passing these beams thru a wave plate the result then passes through the cube with negligible loss, but the unrotated beams striking at a right angle don't reflect with low loss to join the transmitted beam, but loose about 30% to wasted transmission. Tipping the cube to reduce the plane of the interface to less than 45 degrees with the first (rotated beam) reduces the loss of the second beam , but only at the expense of loss in the transmitted beam. Its as if the lasers are not well polarized. To confirm that I didn't just fail to line up the lasers with each other on installation and produced a blended polarization, I tried to orient the cube with just one diode and no matter what orientation the cube would not fully reflect or transmit the beam. I tested two cubes one from Stanwax and one from Connecticut lasers and both preformed identically. Any thoughts?

  2. #2
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    This was already discussed:
    http://www.photonlexicon.com/forums/...s-and-PBS-help

    i solved this problem with non right angle between incomig beams

  3. #3
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    I had seen this thread, and had set up the beam combiner based on the best orientation shown in the photos posted by andy, but when I measured the combined output it was only 80% of the total going into the cube and that's when I began to look at the power in the stray beams ( the cube mount was becoming pretty warm from the unseen and previously unsuspected stray beam striking the mount surface). This is different; no matter how you orient the PBS, I mean tip, tilt or any rotation you can not cause a single diode input to REFLECT without significant stray beams. I also set up the two cubes in series, allowing the stray beam of the first to pass into the second cube which intern split the input into nearly identical transmitted and reflected beams. Weird. The reason I posted this separately is because I suspect the cubes themselves and not their orientation, but before I go out and spend a lot of money chasing the elusive "perfect" cube, is this just a property of a variety of cubes from different sources or a property of the 445 and its polarization?

  4. #4
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    I just did a quick check on the PBS cubes from the GB a while back. Power at the Laser apperture set @ 465mW, PBS transmition 440mW = 94.6%, PBS reflection 440mW = 94.6%. In both cases PBS on beam axis with no tilt/rotation to beam axis. Test Laser is 445nm single diode with cylinder correction (demands on exact diode rotation is very high). I'm not sure, but the beam area on the PBS may play a major roll on losses. In this test the beam area is ~ 3.5 x 3.5mm.

  5. #5
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    Thanks for looking at that. I just tested the cubes rotated 90 degrees relative to each other ie. one reflects and transmits in the horizontal plane while the other operates in the vertical and I would expect complete blockage of the beam passing thru these orthogonal polarizers and I don't. Am I wrong?

  6. #6
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    Quote Originally Posted by planters View Post
    Thanks for looking at that. I just tested the cubes rotated 90 degrees relative to each other ie. one reflects and transmits in the horizontal plane while the other operates in the vertical and I would expect complete blockage of the beam passing thru these orthogonal polarizers and I don't. Am I wrong?
    For the price of these cubes, 5-6% loss is acceptable. I'm sure you could get cubes with losses <1% but that would be a different price class. This 5-6% loss is your stray and absorbtion. You're claiming losses of 20% I can't imagine that just being the PBS, is your diode fast axis rotation absolutly vertical? I prefer to setup diode rotation in the far field (~ 12m) with the collimator defocused to give a 2m line/ellips @ 12m and set the line to absolte vertical rotation, tighten, refocus and place correction optics. Should give highest reflection/transmition.

  7. #7
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    You're right of course that 5-6% loss is acceptable for these low cost cubes. Regarding fast/slow axis orientation however, the freedom to orient the cube ( or the wave plate as I have also tried) in order to achieve minimal loss should compensate for any misalignment in the diode's set up. This issue should only present when I am constrained by working with multiple diodes at the same time through the same cube. I suspect that for some reason the output of my 445 diode (the one I am testing with) is only partially polarized as the stray beam from the first cube seems to contain equal amounts of P and S. Or the cube is only partially polarizing for the same reason.

  8. #8
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    try our new 445nm PBS cube, which is better.
    Best regards!
    Bridge
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    bridge@laser-wave.com or 463366312@qq.com
    We Chat: 463366312, Laserwave-Bridge

  9. #9
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    If I am correct, I may not be, one of these PBS cubes is either the PBS supplied by Stanwzx or CT Laser. Am I correct?

  10. #10
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    Eureka! The PBS cube that I just received from JML Optical is amazing. I ordered a 25.4mm cube optimized for 488nm and right after taking it from the packaging (it was very clean) and placing it into the 445nm beam it reflected a bright image at 90 degrees, but when rotated so as to transmit the cube went completely dark; no surface reflection and only a VERY dim reflected waste beam.
    Oops. I should have said optimized for 458nm.
    Last edited by planters; 07-20-2011 at 20:20. Reason: Typo

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