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Thread: Beam Diameter Trouble For Rgb

  1. #1
    Join Date
    Jan 2007
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    Angry Beam Diameter Trouble For Rgb

    Hi guys,

    I need some advise/ help.
    I intend building a RGB laser, so I bought the following laser modules
    532nm- 250mW, analog modulation
    473nm- 250mW, analog modulation
    635nm- 500mW, analog modulation

    So, after receiving the laser modules I tested all of the to see if all are in a good working oreder? I was so happy to see all of the work!
    After placing the lasers next to each other I noticed that the red laser beam diameter was about dubble that of the other lasers. Green and Blue = 3mm, Red = 6mm. and even stranger is that the resd laser beam is square not round!

    I had informed the supplier of my intentions, building a rgb laser, and he supplied the lasers mentioned above. I don't want to mention the supplier, so after qeustioning him, he said this 6mm square beam is the norm for building rgb lasers.

    Any body that can advise if this is correct? and how could I reduce the size of the red laser beam?

    Any suggestions would be appresiated!

  2. #2
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    Jan 2006
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    Charleston, SC
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    Cool

    Hi Werner;

    Saddly, it's pretty common for the higher power red diode lasers to have lousy beam specs, especially for the 635 nm diodes. The specs you describe are pretty typical for that power range. (Most of them also have funny shaped beams. Squares or ovals are common.)

    Your options are to either 1) live with it, or 2) expand the beams of your green and blue lasers (using a pair of lenses) to bring them closer to the diameter of your red.

    If you decide to live with it, you may find that the larger beam doesn't bother you that much. If you will be doing mostly beam shows you may not notice it that much. If you want to do graphics, you probably will notice it though. It's up to you as to how much it will bother you. (Personally, it would bother me!)

    If you decide to expand the beams on your green and blue, you're going to loose some power through the lenses. (It shouldn't be too much.) It will also require some very precise mounts to get the distance between the two lenses exactly right. (Easiest way is to fix the first lens in position and then mount the second one on a linear translation stage.) This will obviously add to the size (and cost) of your projector.

    In any case, it's not the laser supplier's fault. If you absolutely wanted to match the three beam diameters exactly, you would have needed to specify that when you ordered. And believe me, the price you would have been quoted would have gone *way* up. (That's assuming that the supplier even had a 500 mw 635 nm red laser with a 3 mm beam. I don't know of any diodes on the market right now that could meet that spec. At least, not in my price range! )

    My guess is that the only reasonable way to meet that spec would have been to step up to a 671 nm DPSS red laser. But DPSS red is expensive to begin with, plus 671 nm red appears much dimmer to the eye than 635 nm red, so you would have needed a lot more power, which drives the cost up even higher...

    Adam

  3. #3
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    Jan 2007
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    Question

    Thanks for the suggestions, Buffo

    Sad thing is that I had mentioned the beam diameters need to be simular, and the supplier said they would do there best to get them close. I guess 6mm square is close to 3mm round...????

    I am thinking of building the rig and see what the end result is. Maybe take some corrective steps from there?

    Hey, what about letting the red beam go through a restricting plastic or metal disc with a 3mm hole in the middle?

    Or am I grabing at straws...

  4. #4
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    Watch the divergence go out of control too on that red...
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  5. #5
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    Cool

    Yeah, you can use a pinhole to carve out the center of that red, but you'll loose power in the process, plus like Dave said, the already poor divergence of the red diode will only get worse after passing through the pinhole. (Light waves will diffract around the edges of the hole. Google "Poisson bright spot" for info on the physics involved. Though technically in that experiment everything is reversed, the same optical principles apply.)

    There are a few optical tricks you can try, but you'll always be trading divergence for beam diameter. It's a fundamental law of optics. Still, if you know you'll always be operating with a short throw you can try to optimize your projector for the narrow field, and that might help some. (eg: shrink the beam and realize that the higher divergence won't be an issue with a really short throw.)

    It's unfortunate that your dealer didn't explain things a little bit more; he probably assumed you were familiar with the beam specs of your average 500 mw 635 nm diode. But I don't think he intended to defraud you.

    I agree that you're probably better off building the thing and seeing what you have. Just be sure to leave some room for extra optics if you decide to go that route. (Or you could lay everything out temporarily, get it aligned as well as possible with the temporary mounts, and then look at the resulting beam quality before you hard-mount everything.) Before I tried to improve the red though, I think I'd work on expanding the green and blue. But that's just me...

    Adam

  6. #6
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    This problem is everywhere. Powerful 635... (I call them the big red flashlights) has a horrible specs. What Ive done is to put a Galileans beam expander in reverse. It works great for 20-30 meters. And that enough for my purpose.
    Plus there is another problem 635 beam. It will not fit on fast galvo scanner mirror. So you will loose about 20-40%

    Oh yeah forgot to mention...powerful 635 normally has square beam.
    Last edited by Dr Laser; 06-15-2007 at 03:28.
    I hired an Italian guy to do my wires. Now they look like spaghetti!

  7. #7
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    Quote Originally Posted by Dr Laser View Post
    Plus there is another problem 635 beam. It will not fit on fast galvo scanner mirror. So you will loose about 20-40%
    Unless you use large aperture scanners
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  8. #8
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    Cool

    Quote Originally Posted by dave View Post
    Unless you use large aperture scanners
    Yeah, at the expense of degrading speed and performance.
    Good for beam shows but crappy for graphics.

    Better to shrink down your beams to fit on a small set of mirrors so you don't sacrifice performance and shorten the lifetime of your galvos.
    Profile Redacted by Admin @ 04.24.2010

  9. #9
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    If you shrink a 635 beam, the divergence is going to go thru the roof. And its bad to start with...
    KVANT Australian projector sales
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    Lasershowparts- Laser Parts at great prices
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  10. #10
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    Jan 2007
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    Talking Scanners

    Ok, so I will have to live with the fact that i should have done my homework better. Could have had 2 red lasers in the hope of beter beam quality?

    Anybody know where or who can supply me with DT40 scanners in a short time? Apparently they are good?? and I need a set ASAP !

    While building the rgb rig, I was wondering what the size of the DT40 scanners components are, wouldn't want to cut short on the Aluminium base...

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