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Thread: driver circuit for DVD burner diode laser

  1. #11
    Join Date
    Nov 2005
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    Quote Originally Posted by Buffo
    In other news, I finally finished my power supply for the ISOMET AOM... Hooked everything up, only to discover that the damn driver for the AOM needs more than 1.5 amps. (My voltage regulation circuit is based on the LM317, which can't deliver more than 1.5 amps!) ARGH!!!! So now I've got to wire in a big transistor as a pass bank. I've got everything I need except for the high wattage input resistors, so that means waiting another week for stuff from Digikey... (Unless by some miracle Radio Shack carries .3 ohm, 5 watt resistors!)
    I have taken a big liking to the lm2576 switching regulator. A much tidier solution than a regulator and extra pass bank transistors And they stay so cool too, in most cases forget about a heatsink

  2. #12
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    Jan 2006
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    Dave;

    I took your advice and looked at the LM2576, but I see that it only does 3 amps. I need more than that, so I'd still end up using a pass-bank.

    (Also, I screwed up in my earlier post - the LM317 can deliver 2 amps, not 1.5.)

    Update: I got my power supply completed and it is capable of delivering up to 6 amps right now, which is enough. I've sucessfully powered up the AOM driver board, but I can't get it to do anything. Don't know if there is another circuit that I need to tie into in order to activate the blanking or what... Guess I need to hook up my oscilloscope and look at the RF coming out of the thing. Sigh.... The project that never ends!

    Groover:

    Tried checking that link you posted, but the page seems to be down.

    Adam

  3. #13
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    Assuming power and voltage are correct...

    Did you pass the laser through the AOM at a bragg angle?
    The AOM will need to rotate ('pan') in relation to the source laser.
    You'll want to rotate until you see a diffraction grating like burst.
    Then you rotate the laser itself (or the AOM itself in a 'roll') to tune
    for optimal extinction.

    If you don't have polarization or the bragg correct, the aom will act
    like nothing more than an expensive piece of glass.

    http://www.neostech.com/PDFs/Asize%5C51%5C51A11958.pdf

  4. #14
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    Wow! Thanks Yadda...

    I obviously didn't have a clue what I was doing. ops:

    No, I did not have the laser adjusted to a bragg angle. I had the beam entering parallel to the aperatures (incidence normal). And just as you stated, it acted like an expensive hunk of glass.

    I guess I need to build a decent mount for this thing before I continue experimenting with it. It sounds like alignment is more crucial than I originally planned.

    Also, I'm guessing that a DPSS pointer will not be a suitable source to test it with, since the polarization may change - right? It won't be hard to hook up a hene, or even one of my argons, to use as a source for these tests, so I suppose that's the route I should take.

    Hmmm... The optimum bragg angle is going to change based on the frequency of the laser, isn't it? So if I'm going to use this on an argon, I'd better test it with an argon I guess...

    The .pdf you linked to gave a formula for calculating the proper bragg angle, but I don't think my crystal has the same acoustic velocity. (Mine is an Isomet 1205C-1) If the velocity is the same, then that formula yields a bragg angle of just .26 degrees for 488nm light, which is pretty close to incident normal.

    I guess I need to play with this some more...

    Adam

  5. #15
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    .29 degrees doesn't sound right... you should definitely be able to see the angle... If you have a bragg mount or a rotary table which you can lock, I'd
    just roughly match polarization and rotate back and forth till you get a burst.


    http://www.neostech.com/PDFs/Asize%5C51%5C51A9220.pdf

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