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Thread: Beam expander after scanners.. possible?

  1. #1
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    Default Beam expander after scanners.. possible?

    I am tasked with a fairly long distance laser projection, and need to get divergence low as possible in the far field (say 500 meters distance).
    I remember someone talking about a lens system placed directly AFTER scanners, which reduces divergence at the expense of narrower scan angle. Could this just be a simple beam expander?
    I know the scanned beam changes things significantly vs a static beam, and one would have to account for increased entrance and exit diameters, but is it theoretically possible if you can avoid "clipping" the edges of the beam expander? The actual scan angle would be really low, maybe 5 degrees so it would not be the typical 50 degree scan angle one usually sees in shows.

    Forgive me if I am trying to break the laws of physics here, I am no optical knowledge. I just remembered this and it got me thinking. I worry that I may missing something fundamental but felt I had to ask.
    Last edited by Humphry; 06-25-2018 at 13:32.

  2. #2
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    ... this would be a much more complex f-theta-optics with some more lenses and much, much, MUCH! bigger ...

    Viktor

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    Quote Originally Posted by VDX View Post
    ... this would be a much more complex f-theta-optics with some more lenses and much, much, MUCH! bigger ...

    Viktor
    Ah I see, I had this vision of just reversing Pangolin's Safety Scan Lens. Thanks for clarifying.

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    Humphry
    I have the same idea as you and I found a galvo with lens, may be it is you are looking for

    https://www.thorlabs.com/newgrouppag...tgroup_id=6057

    Attachment 54256

    I don't know how lenses it uses.....

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    ... I see only galvo-heads with bigger mirrors for large beam diameters, no secondary beam-expansion - they could be used for wider focus distances, but not really this difference to expect.

    On the other hand - with really wide focus distances the plane-field distortion is negligible, so no need for the f-theta - only a big beam-expander, to catch the complete beam angle ...

    Viktor

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    Quote Originally Posted by francisco View Post
    Humphry
    I have the same idea as you and I found a galvo with lens, may be it is you are looking for
    https://www.thorlabs.com/newgrouppag...tgroup_id=6057
    I don't know how lenses it uses.....
    This is EXACTLY what I was thinking, but you linked to the scanners and not the lenses. Obviously we could just use larger mirrors at the expense of scan speed, but I would much rather reduce scan angle. Here are the "after scanner" scan lenses for Viktor to have a look at: https://www.thorlabs.com/newgrouppag...tgroup_ID=6430
    The lens "slots" directly in front of the galvo mirrors, AFTER they have already scanned an image. Perhaps beam expander is the wrong terminology - all we need to do is make the image smaller, and thus reduce the thickness of the laser beam equal to the size of the projected image. ie: Half image size, and half beam thickness. Or does this just sound ludicrous? Let me get in touch with someone at Thorlabs and ask.

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    ... it's a bit different -- for best divergence (smallest spot diameter) in 500m distance you'll need a BIGGER beam diameter before or after the galvos!!

    A beam-expander before the galvos (and corresponding bigger mirrors) is much cheaper but will slowdown the scanner ... beam-expanding after the galvos will drastically increase the optical dimensions and the price!

    Viktor

  8. #8
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    Quote Originally Posted by VDX View Post
    ... it's a bit different -- for best divergence (smallest spot diameter) in 500m distance you'll need a BIGGER beam diameter before or after the galvos!!
    A beam-expander before the galvos (and corresponding bigger mirrors) is much cheaper but will slowdown the scanner ... beam-expanding after the galvos will drastically increase the optical dimensions and the price!
    Viktor
    Ok, understood. If it's not feasible then no point pursuing. Cheers.

  9. #9
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    Quote Originally Posted by VDX View Post
    ... I see only galvo-heads with bigger mirrors for large beam diameters, no secondary beam-expansion - they could be used for wider focus distances, but not really this difference to expect.

    On the other hand - with really wide focus distances the plane-field distortion is negligible, so no need for the f-theta - only a big beam-expander, to catch the complete beam angle ...

    Viktor
    In the bottom of the page there is an image of the galvo I mentioned...

    https://www.thorlabs.com/newgrouppag...tgroup_id=6430

  10. #10
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    ... I can't see any secondary beam expansion optics -- all of them seems to be standard f-theta for collimated beams ...

    Viktor

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