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Thread: Back reflection killing maXYZ module?

  1. #1
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    Default Back reflection killing maXYZ module?

    I sent my 225mW 660nm maXYZ module back to Chuck because it just suddenly died one me. The beam got very dim and the module got too hot to touch. He claims it is caused by beam back reflections. What would cause this besides putting a mirror in front of the module? It never had any optics in front of it and it was always sitting on a 1/2" aluminum breadboard with nothing under it. Has this happened to any of you? I feel bad that it died, but I have to pay $120 to get it fixed and I really don't want that to happen again.
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  2. #2
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    Because the module got too hot, I was thinking of a short-circuit between the diode's case and the ground of the driver (the maXYZ diode's positive pole (cathode) is the case).
    Is it a chance that you connected the alu baseplate together with the case of the diode module (the brass part) ?

  3. #3
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    I don't see how I could have done that. It was just sitting on the bread board.
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  4. #4
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    Was just a supposition... Maybe you adjusted the focus of the laser with a screwdriver, and touched at the same time the laser and the breadboard?
    Or is it the module that had was defective...

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    Quote Originally Posted by Laser Ben View Post
    What would cause this besides putting a mirror in front of the module?
    The beam reflecting off something shiny in the room and bouncing back into the module... Something as crazy as your metal belt buckle even. You walk in front of the laser and for an instant everything lines up. Poof!

    Back-reflection can kill a diode in a matter of NANOSECONDS. No, scratch that. It happens in less than a nanosecond. Here, from Sams Laser FAQ:
    Another possibility is that the return beam from the mirror precisely hits the output facet of the laser diode. While this is a very small area, it only needs to happen for an instant. The result is an extended cavity which suddenly has a much lower loss due to the higher reflectance of the external mirror compared to the cleaved facet. The result is a virtually instantaneous increase in intracavity power and if the laser was running close to the COD (Catastrophic Optical Damage) limit, poof goes the laser diode. This would be more likely with a constant current driver but even in constant power mode, the increase in intracavity power would take place in less than 1 nanosecond - much less than the response time of the feedback circuit.
    You have to be very careful with a direct injection diode. Especially if you're operating it close it it's absolute limit. I've heard of people killing laser diodes while trying to measure the power output with a lasercheck wand because the small reflected beam from the wand made it back to the diode face. The risk of failure is greatly reduced if you're not running at full power. But when you're near the max power limit, you are in the danger zone.
    I feel bad that it died, but I have to pay $120 to get it fixed and I really don't want that to happen again.
    Yeah... I hear you. At least take solace in the fact that you bought a Maxyz module and Marconi is only charging you $120 to fix it. If you had bought a diode from anyone else, you'd be paying full price for a replacement. (Diode failure due to facet damage is easy to discern using a relatively low power microscope, so it's not something that you can hide.)

    When you build your projector housing, always keep back reflection in mind. Even if the reflected beam has to pass through a couple optical components (dichros, pbs cube, etc) in order to get all the way back to the diode face, it can *STILL* cause it to die. So be mindful of anything that can cause a beam to be reflected back. I purposefully mounted my galvos such that it was impossible for them to rotate far enough to send the beam back to the lasers, even if the amps failed and sent the mirror shafts hard over.

    Adam

  6. #6
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    Hm, so I think, marconi overdrives his diodes... Never heard about red laserdiodes over 150mW CW!!!

    You CAN overdrive them, but 225mW??? ouch...

  7. #7
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    hmmm...
    i don't own one of them but everyone here who does has only good things to say about them and marconi.
    hopefully laser ben will get to the bottom of what happened but i don't see any complaints about any problems from overdrive.
    peace,
    wes

  8. #8
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    It was a great module. Nothing wrong with it up until it died. And yes you can have red diodes up to a couple watts. They have large emitters and are multimode but it can be done.
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  9. #9
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    Hey Adam,

    Yet another pearl of wisdom you pass on to us newbies..

    When you build your projector housing, always keep back reflection in mind. Even if the reflected beam has to pass through a couple optical components (dichros, pbs cube, etc) in order to get all the way back to the diode face, it can *STILL* cause it to die. So be mindful of anything that can cause a beam to be reflected back. I purposefully mounted my galvos such that it was impossible for them to rotate far enough to send the beam back to the lasers, even if the amps failed and sent the mirror shafts hard over.

    I was about to ask, given that I have one of Chucks dual Maxys whether or not one gains any added "protection" via the cube,mirror and dichro.
    This has been a good wake up call for me to be careful as well.

    Is this back reflection problem as bad with DPSS lasers ??

    During setup, when "stuff ups" are more likely to occur does running the laser at very low output offer any degree of protection ??

    Cheers

    Ray
    NZ

  10. #10
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    Quote Originally Posted by Laser Ben View Post
    It was a great module. Nothing wrong with it up until it died. And yes you can have red diodes up to a couple watts. They have large emitters and are multimode but it can be done.
    Sure, I know that. Ok, you could have missunderstand me. There are diodes with a few watts red
    But you said it already: They have big (too big!) emitters, so you want be able to get a nice beam out of them

    Marconis moduls looks nice, but I think, he uses normal 5.6mm or 9mm-diodes with 40-60um-emitter. In this case, there are no diodes over 150mW!
    So I think, he overdrive them a lot! Sometimes it works, sometimes not, like your problem now...

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