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Thread: PBS cube - What am I doing wrong?

  1. #1
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    Default PBS cube - What am I doing wrong?

    Hi,
    I have two diodes in mounts as shown in the attached pics. They are driven by Robins module.
    The beam that goes via the mirror (diode 1) is fine.
    The beam from diode 2 is the problem.
    However I rotate the diodes ( that is what the screws in the casing are for), the brightest beam goes straight through the cube. If I rotate diode 2, I can get the relected beam to almost zero, but the opposite is what I want. The beams are purposley mis-aligned so I can see the relative brightness of each.
    I have tried swapping the diodes about, but no difference.
    Anybody have any suggestions?

    Thanks, David
    Attached Thumbnails Attached Thumbnails PBS1.jpg  

    PBS2.jpg  

    PBS3.jpg  


  2. #2
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    Have you tried turning the cube around?
    Quote: "There is a theory which states that if ever, for any reason, anyone discovers what exactly the Universe is for and why it is here it will instantly disappear and be replaced by something even more bizarre and inexplicable. There is another that states that this has already happened.... Douglas Adams 1952 - 2001

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  4. #4
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    Hi,
    Yes, tried cube everywhichway ( I think).
    Should have said - third pic is with mirror out of the way .
    You can see that the transmitted beam through the cube is much brighter than the refelected one however I turn the diosed.
    Regards, David.

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    turn the diode cases till the beam does not go through
    Eat Sleep Lase Repeat

  6. #6
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    Quote Originally Posted by xntrix View Post
    If I rotate diode 2, I can get the relected beam to almost zero, but the opposite is what I want.
    Hi David
    The point where you get the reflected beam to almost nil should be 90 degrees away from the maximum point. If you rotate that diode (diode 2) through 360 from where it is at the null point, the reflected beam should rise and peak, then fall back to null, then rise once more before coming back to null at the 360 degree point. Rotating the cube as Jem suggested should not make a difference unless the cube is rotated through 90 degrees about an axis formed by the incoming beam.
    Do your mounts for your diodes (with the handles removed) allow for a complete rotation? if so does making the 360 circle do as I suggest above?

    Rob
    If you need to ask the question 'whats so good about a laser' - you won't understand the answer.
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  7. #7
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    One more thing.... try peaking each laser individually if they are on a common driver (which it looks like they are) then block the beam with a bit of card and try peaking the other diode.

    Rob
    If you need to ask the question 'whats so good about a laser' - you won't understand the answer.
    -----------------------------------------------------------------------------------------------
    Laserists do it by the nanometre.

    Stanwax Laser is a Corporate Member of Ilda

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  8. #8
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    Quote Originally Posted by stanwax View Post
    Rotating the cube as Jem suggested should not make a difference unless the cube is rotated through 90 degrees about an axis formed by the incoming beam.
    Well articulated Rob. That's what I was trying to say but you put it much better. It must be something to do with late nights and lack of sleep

    Jem
    Quote: "There is a theory which states that if ever, for any reason, anyone discovers what exactly the Universe is for and why it is here it will instantly disappear and be replaced by something even more bizarre and inexplicable. There is another that states that this has already happened.... Douglas Adams 1952 - 2001

  9. #9
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    Quote Originally Posted by Jem View Post
    It must be something to do with late nights and lack of sleep
    I dunno - you young 'uns just cant cut it

    Rob
    If you need to ask the question 'whats so good about a laser' - you won't understand the answer.
    -----------------------------------------------------------------------------------------------
    Laserists do it by the nanometre.

    Stanwax Laser is a Corporate Member of Ilda

    Stanwax Laser main distributor of First Contact in UK - like us on Facebook http://www.facebook.com/FirstContactPolymerCleaner
    www.photoniccleaning.co.uk

  10. #10
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    OK David I may have an answer.
    You need a wonky cube.

    I have long advocated angling PBS cubes and have mentioned it on here several times but without it raising much interest.
    So as David is having trouble, and I sold him the cube I decided it was time for some figures.
    Using a red diode laser measuring 105mW with lasercheck. Firstly I pointed it at a cube and peaked/nulled the beam so that its orientation was throwing the beam out of the side of the cube. With it peaked I was getting 85.6mW reflected and 2.06mW thru.
    Next I turned the diode thru 90 and peaked it to get 7.34mW reflected and 84.7mW thru.
    I suspect that David is seeing this effect in that one orientation passes more to the waste position than the other - though the difference to the used beam is very little (1% ish).

    Now I repeated the above but turned the cube (sat a top a rotary stage with angular markings). Again I get different results depending on the orientation of the diode.
    First as before with the beam reflecting within the cube, I turned the cube through a massive 29 degrees and get 94.0mW reflected and 0.13mW thru.
    Second test with the useful beam going thru I found the null at around 15 degrees which gives 92.4mW thru and 0.53mW reflected.

    That is why the cube in my dual red is canted!

    Discuss.

    Rob
    If you need to ask the question 'whats so good about a laser' - you won't understand the answer.
    -----------------------------------------------------------------------------------------------
    Laserists do it by the nanometre.

    Stanwax Laser is a Corporate Member of Ilda

    Stanwax Laser main distributor of First Contact in UK - like us on Facebook http://www.facebook.com/FirstContactPolymerCleaner
    www.photoniccleaning.co.uk

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