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Thread: Galvo/Amp Upgrade

  1. #31
    Join Date
    Nov 2019
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    West Chester, PA
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    Quote Originally Posted by buffo View Post
    A Keplerian collimator can be used to expand or contract the beam diameter, yes. But in this application the idea is to use identical lenses on either end of the collimator so the output beam is identical to the input beam. The idea is not to change the beam diameter but to position a spacial filter (the pinhole) at the focal point in the middle between the two lenses. This allows you to "carve out" the center of the beam. And since the beam is converging to a point as it passes through the pinhole, any stray light that diffracts around the edge of the pinhole will spread out far enough that it will completely miss the second lens and thus will not be present in the output beam.
    So, if I am reading this right and understand correctly, there will be two identical lenses and the idea is to first make the beam diameter smaller with the first lens? Then you would carve out the beam with the "pinhole" and then the other lens is put at the other end after the pinhole to upconvert essentially, back to the original beam only with the pinhole having corrected the beam into a perfect circle? Ideally, would i do this for each individual laser or after the lasers have been combined?


    Quote Originally Posted by buffo View Post
    Most commercial RGB modules list the beam diameter and divergence, so it's easy to make sure that whatever you buy will work with your scanners. Be sure to measure the width of your mirrors first though, because there is a big difference between a 4 mm wide mirror and a 4 mm *aperture* mirror. (Because the mirror is positioned at an angle to the beam the mirror must be wider than the beam to capture the whole beam.)
    So, I have the compact 506's 4mm. Say I were to go the route of buying collimated RGB laser module such as this for instance. Would it work? I am not sure I understand what it means showing the different beam sizes. Could that be for the distance from the laser?

    Or, just for reference, this laser module am I looking at the 5.6mm as the beam size?

    Thanks again!

  2. #32
    Join Date
    Jan 2006
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    Charleston, SC
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    Quote Originally Posted by jdavis7765 View Post
    So, if I am reading this right and understand correctly, there will be two identical lenses and the idea is to first make the beam diameter smaller with the first lens?
    The first lens in a Keplerian collimator converges the beam (focuses it to a point), but beyond that focal point the beam begins to expand again. (The beam is now flipped in orientation, but that's not important.) When the beam has expanded back to it's original size, that's where you should position the second lens. That second lens re-collimates the beam so it's parallel again.

    Thus you have a 1:1 collimator. It doesn't really do anything to the beam (apart from flipping it, which is only relevant if we were talking about an imaging system). The key is the focal point in the middle, as that is where we will position the pinhole spacial filter.

    Then you would carve out the beam with the "pinhole" and then the other lens is put at the other end after the pinhole to upconvert essentially, back to the original beam only with the pinhole having corrected the beam into a perfect circle?
    Yup! Exactly right.

    Ideally, would i do this for each individual laser or after the lasers have been combined?
    After all beams have been combined, but before the scanners.

    I have the compact 506's 4mm. Say I were to go the route of buying collimated RGB laser module such as this for instance. Would it work?
    The goldenstar module you linked to lists the beam width at the laser aperture as 2 mm by 5 mm. The 5 mm axis is too wide for your scanners. You can probably clean that up with a spacial filter (as described above), or just accept that you'll have a small amount of the beam spilling off the scanner mirrors when you scan wider than 45 degrees.

    I am not sure I understand what it means showing the different beam sizes. Could that be for the distance from the laser?
    Yes, the "at aperture" measurement is beam width and height at the output of the laser module. The rest of the measurements are at 5 meters away, 10 meters away, and 15 meters away from the output window of the laser module. The beam gets bigger due to divergence. Also, there are two beam width measurements because the module uses multi-mode diodes with rectangular beam profiles. (See fast and slow axis explanation above.)

    Or, just for reference, this laser module am I looking at the 5.6mm as the beam size?
    No. On that website they are talking about the physical size of the diode module itself. 5.6 mm is a common diode can size. 9 mm is another common diode can size. Neither of these two measurements have anything to do with the size of the output beam.

    When buying a bare diode you need to know the size of the diode can (basically the diameter of the can) so you can purchase the same size diode module to mount the diode in. This often gets confusing, because the module will have two sizes listed: One is for the diode can diameter and the other is for the total outside diameter of the module. Typical outside diameters for modules on DTR's site are 12 mm, 20 mm, and 25 mm.

    Adam

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