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Thread: 445nm split and recombine beam?

  1. #51
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    Jan 2007
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    Hello David, good to hear from you.
    So you do use that method in your lasers?




    _____________________________
    @ Laserkits-
    Yes, I believe we need an optics expert to define the anatomy of the diode laser beam itself and the ramifications and expected results of of modifying it. In my experience you cannot chop 1/2 of the beam off nearfield (at the aperature) and see results farfield other than it getting dimmer, like losing 1/2 the power but the divergence and dimensions seem to stay the same. When put through an aspheric lens it looks like this:
    I always wondered why it shifts 90 degrees instead of 180.
    Click image for larger version. 

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  2. #52
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    Quote Originally Posted by laserkits View Post
    Not so in this example, which is the one I was speaking about.
    http://www.photonlexicon.com/forums/...chmentid=19664
    http://www.photonlexicon.com/forums/...chmentid=19668
    In this configuration the retro bouncer has taken one half of the slow axis, turned it 180 degrees about its axis (not 90) and then stacked it with the remaining half of the slow axis. In this configuration you will have a skinnier rectangle at a distance than you would if you did nothing at all... The aspect ratio of the diverged beam has increased, not decreased, so this has made the beam worse and not fixed anything...
    You have to remember that you are working in the near field of the laser here. The divergent or "fast" axis is the skinny one.

    Of course there is also some divergence in the slow axis so the above diagram is not exact, but shows how the beam changes over distance.
    OK, but why would you want to flip the beam around entirely and then wave-plate it to change its polarization? What's the point of turning a beam upside down, aside from lengthening the beam path for one half of it?

    If you use a retro bouncing setup that turns the beam 90 degrees on its side (pick it off first, then go straight up, down, level again and loop back into the PBS) you'd basically have two matching fast axes. They may both be highly divergent, but a cross beam pattern looks a lot better and could even be more efficient through a pinhole.

  3. #53
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    Jan 2007
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    No. My opinion is that method mixed the polarization.
    We keep the linear polarization of 1w 445nm. So it is easy to get nice 2w 445nm beam.

    0QUOTE=steve-o;208318]Hello David, good to hear from you.
    So you do use that method in your lasers?



    _____________________________
    @ Laserkits-
    Yes, I believe we need an optics expert to define the anatomy of the diode laser beam itself and the ramifications and expected results of of modifying it. In my experience you cannot chop 1/2 of the beam off nearfield (at the aperature) and see results farfield other than it getting dimmer, like losing 1/2 the power but the divergence and dimensions seem to stay the same. When put through an aspheric lens it looks like this:
    I always wondered why it shifts 90 degrees instead of 180.
    Click image for larger version. 

Name:	LD beam properties.png 
Views:	44 
Size:	7.3 KB 
ID:	27739[/QUOTE]
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  4. #54
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    Quote Originally Posted by Lasever View Post
    No. My opinion is that method mixed the polarization.
    We keep the linear polarization of 1w 445nm. So it is easy to get nice 2w 445nm beam.
    OK, if you use that setup for one half of a multi-diode setup I can fully understand it, as it would concentrate more power into the center of the PBS when combined with the other half.

    The technique of 'chop, rotate, recombine' would probably work well with a single.

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