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Thread: 445nm beam collimation/correction

  1. #11
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    Hi Marc,

    Couldn't have said it better, exactly my thoughts to.

    I was thinking matt black painted piece of very thin shim maybe?

    What have peoples experience been using pin holes?

    Also, what materials, thicknesses, colours and surface finish did you have success or failure with?

    Thanks
    Kit

  2. #12
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    Marc,

    It doesn't seem like it would work to me. I'm far from well versed in optics, so this is just a thought.

    I would think that the center of the beam that passes through the pinhole is diverging at the same rate as the outer part of the beam, so all you are doing is weakening the beam and giving it a nice shape very close to the diode, but it will still diverge wildly outside of the projector where it counts.

    Ian

  3. #13
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    Quote Originally Posted by gottaluvlasers View Post
    Excellent tests and results! Solarfire- thank you for taking the time to do these extensive tests.

    My question is *still* why nobody is using a pinhole to shoot their beams through?!? Am i not taking something into account with the useage of pinholes? does it add any sort of beam crap?

    With the price of blue the way it is- WATTS of power for <$500 (Home brews) why are we not using pin holes to just circle the beam out? Who cares about losing a watt of power (just say 2W in to get 1W out of a pin hole).

    Im sincerely wondering why this isnt being used. I am starting to believe that perhaps "pinholing" adds some sort of interference or something in the beam?

    Any ideas?

    -Marc

    What you're describing is a spatial filter, and to get good results without adding a ton of crap to the beam the filter needs to be either a commercial model or very carefully built. The pinhole needs to be extremely tiny, so much so that the hole itself is all but invisible. The beam is then focused to a point and the filter pinhole placed precisely at the focal point using very precise mounts. If everything is set up right, the output should be very nearly perfect TEM00. If you take one of these 445nm diodes and focus it down, the smallest focal point will be a line, just the same as if it's collimated to infinity. If the pinhole is properly sized and round, only a circular part of the focused line will make it through, the rest will be lost.. given the challenge of setting this kind of system up, coupled with the losses, I believe it would be simpler to couple the output from these diodes into fiber to get round output.. but either way it's a challenge..

  4. #14
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    Quote Originally Posted by ireedz View Post
    Marc,

    It doesn't seem like it would work to me. I'm far from well versed in optics, so this is just a thought.

    I would think that the center of the beam that passes through the pinhole is diverging at the same rate as the outer part of the beam, so all you are doing is weakening the beam and giving it a nice shape very close to the diode, but it will still diverge wildly outside of the projector where it counts.

    Ian
    You are correct,

    the beam exits the collimator like this:" | " a vertical line but diverge into a vertical stripe like this ---- so shaping it right after the diode with a pinhole makes no real sense your galvo mirrors are already doing this.

    @ Frank, have you already tried scanning the beam?

  5. #15
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    Quote Originally Posted by mccarrot View Post
    You are correct,

    the beam exits the collimator like this:" | " a vertical line but diverge into a vertical stripe like this ---- so shaping it right after the diode with a pinhole makes no real sense your galvo mirrors are already doing this.

    @ Frank, have you already tried scanning the beam?
    It actually makes a lot of sense, since whatever beam profile cleaning the galvos provide is nowhere near what could be accomplished with a spatial filter. Filtering can get you exceedingly close to TEM00 if the implementation is good.. but you'll still need to collimate the filter's output using proper optics.

  6. #16
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    I was talking about a simple 3mm aperture in front of the beam, not a super duper spatial filter or fibre solution.

  7. #17
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    Ahh.. unfortunately you're right then.. simply making an aperture won't do much for the beam shape.. unless a true spatial filter is used, most of the problematic beam issues will go right through an aperture. A well known example is the various attempts at using apertures to get rid of the little "wings" that re found in the output from LOC diodes. Even after the beam passes the aperture, the wings are still there.. they might be slightly shorter, but they're still there. Apertures can help reduce the amount of scatter around the beam, but even then quite a bit will get through.

  8. #18
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    Quote Originally Posted by ElektroFreak View Post
    A well known example is the various attempts at using apertures to get rid of the little "wings" that re found in the output from LOC diodes. Even after the beam passes the aperture, the wings are still there.. they might be slightly shorter, but they're still there. Apertures can help reduce the amount of scatter around the beam, but even then quite a bit will get through.
    But do you really find it a problem during scanning?
    Have you ever had a customer saying, this beamshow sucks because I had seen "wings" around the red.
    Or these graphic really sucks because everything is red???

    I really don't see the problem.

    we now have affordable 445nm power with reasonable beam specs and we are nitpicking about something a normal person would never notice in a projector.

  9. #19
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    Quote Originally Posted by mccarrot View Post

    @ Frank, have you already tried scanning the beam?
    Judging my workload at the moment, I doubt I will get around to making the setup before the weekend, but I will definitely give it a try and let you know the results.

    I have also given it some thought to maybe limit the beam after the prism or cylinder correction (probably cylinders for getting down to 1-1.2mrad) with an adjustable knife edge aperture above and below the fast axis where the main trash is happening. I’m hoping to finalize a beam at 1 x 1-1.2mrad.

    Quote Originally Posted by mccarrot View Post
    But do you really find it a problem during scanning?
    Have you ever had a customer saying, this beamshow sucks because I had seen "wings" around the red.
    Or these graphic really sucks because everything is red???
    It’s not what others think, I’m my own stumbling block, a nit picking perfectionist

    Yeah.. I know, I’ve got a fu?*in tick and it’s called perfect or not at all!

    Just another brainstorming thought, has anyone tried to first collimate just the fast axis with a cylinder to about equal the slow axis divergence and then collimate with a longer FL aspheric collimator? Or is there a major thinking error in this thought?


    By the way can you tell me the FL of your lens?

    Frank

  10. #20
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    Quote Originally Posted by Solarfire View Post

    After cylinders:
    Not tested!!
    Not further apprehended due to excessive aberration in the aspheric collimation. See Pictures!
    Curious if you tried adjusting the collimator focus after putting the cylindrical lens in the beam path?

    I found with my flexible mirror corrector or with cylindrical lenses the far field spot can be cleaned up a lot with small adjustments to the collimator.

    i have done power measurements with the o-like 405/445 and with the 405-g-2 and 405-g-1. The 405-g-1 and 405-g-2 measure exactly the same. The o-like with the half threads had only 12% less output than the 405-g-X. Not bad really.

    I think the most economical solution is to use the o-like lens and reduce the FA with prisms or lenses so it fits on 3mm scanners.

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