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Thread: Back reflection

  1. #1
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    Question Back reflection

    I have been having bad luck with back reflection on some 660nm diodes... Does this problem happen with 635nm diodes also? If yes, are the 635nm diodes as bad?
    Love, peace, and grease,

    allthat... aka: aaron@pangolin

  2. #2
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    Default

    Quote Originally Posted by allthatwhichis View Post
    I have been having bad luck with back reflection on some 660nm diodes... Does this problem happen with 635nm diodes also? If yes, are the 635nm diodes as bad?
    Never had anything even remotely related to that with CNI modules.
    And BTW
    I hired an Italian guy to do my wires. Now they look like spaghetti!

  3. #3
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    Cool

    *All* direct injection diodes are susceptible to damage via back-reflection. See this section of Sam's laser FAQ for the details. (Start reading at the 5th paragraph down from where the page loads.)

    The key is that 635 nm diodes aren't normally running right at the ragged edge of their performance curve. They appear brighter (because the eye responds better to orange than to red), so they don't need to be pushed as hard to get the same brightness.

    660 nm diodes appear very dim to the eye, so you need as much power as you can get to make up for this. That encourages people to run them wide-ass open, and that's when you run the risk of killing them with back-reflection.

    For example, at full power the Maxyz modules are usually running within 5 percent of their absolute maximum output. (Which is way above their rated output.) So if you reflect the beam back when it's running flat out, you just exceeded the max power by 95%. That's enough to cause instant, catastrophic damage to the output facet of the diode. Poof! No more laser.

    But if you take a 635 nm diode and crank up the power until it's right at the very edge of what it can take, and then reflect the beam back into the diode, you'll kill it just like a Maxyz module. (Most drivers for 635 nm lasers won't let you crank up the power that high though.)

    Here's an old thread that talks some more about back-reflection.

    Adam

  4. #4
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    Wink

    Quote Originally Posted by Dr Laser View Post
    Never had anything even remotely related to that with CNI modules.
    And BTW
    Pictures of what? A laser that doesn't work...? I picked up a 250mW 635nm CNI; I'd like to see some detailed pics of your collminator set up you got going. I got two collminators out of a grocery store scanner I'd like to see if I can tame this beam a little so I can get more on the damn mirrors.

    Thanks Adam. I Am afraid to play with the collminators at the moment, but need to to get this thing on the mirros. I will turn the power down if I try to mess with it.

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