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Thread: Pcaom desperation

  1. #1
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    Default Pcaom desperation

    Hi all !
    My name is Andrew, i'm a hobby laserist from Italy.
    This is my first post here, but i'm a reader of photonlexicon from mounth ago.
    I have a big trouble on a Neos 8ch pcaom. I've read another topic about, but at the end i don't know if user solved the problem or not.

    Well, the waste beam is very strong, really very strong. I've checked polarization, angle, voltage, nanometers...all.
    The modulator works, 16 million of colors (in withelight) and perfect blanking, but the beam to scan is very weak compared to waste beam.
    Pcaom is driven by a QM2000, and i've test the system with my ALC909 with argon and a Coherent highlight Ar/Kr...same results.
    Plese help me: I don't have pover meter so i need a empirical method to understand if the waste beam so bright is normal or not.

    Thank you.
    Last edited by Vega; 07-25-2007 at 06:56.

  2. #2
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    vega,welcome.
    just a guess,but check in your software to see if maybe the output is on lower than 100%.

  3. #3
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    Sure, of course.
    I've done another test too : Disconnected the qm2000, i've putted +5V on positive pin of one channel (es Krypton red) and grounded the negative. The red wavelenght is selected, but in the waste beam there is still a lot of red component, not just a 20%.
    Then i've checked with a scope the signals between pc and driver board, voltage is strong enough to drive at 100% : +/- 5V referred to ground.


  4. #4
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    Set up a show that blinks at 1/2 hertz with a large blue square. align on blue. The factory tunes the pcaom on 488 blue.

    low power is often caused by the wrong polarization, rotate the pcaom head 90' and see if its better.

    you have to move the beam around in the crystal to find the "sweet spot"
    once your sure you have the polarization right, move the low frequency tuning switch for each channel a few positions right or left for peak brightness. write down the settings before moving.

    Low red is usually low RF level or off frequency.
    for example 633 red tuning may slightly modulate 647.

    you may have a driver that is not matched to your crystal and has low Radio Frequency power. find a amateur radio operator or university lab that has a power meter, no RF channel may output more then 125 milliwatts to the crystal when full on. Some newer pcoams, the limit is less then that. The driver may output much more per channel, so you need a RF power meter. Also make sure your cable has a 50 ohm RF impedance, and is not 75 ohm impedance (cable TV surplus) A spectrum analyser or RF power meter is a must, you should not turn the RF power adjustments without one. You may however tune the frequncy adjustments.


    There are several accousto optic orders in the crystal, each will modulate, but only one angle is correct, so you must try many angles. If the connector is pointing toward your baseplate, angle it about 13 degrees away from the laser and work from there.

    also, if the crystal is backwards, ie your going through the exit window first, all hell breaks loose.

    a solar cell, a low cost voltmeter and a uncoated piece of glass as a beamsplitter may help you as a tuning aid.


    Steve Robets
    Last edited by mixedgas; 07-25-2007 at 09:22. Reason: mispell

  5. #5
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    Mr. Roberts, is a honour to be helped by you.

    At very low scanning speed, with a big blue square, beams of first and zero order blink alternately, so i suppose to be in the right way.
    Then i've checked the argon green and seems ok, just a small amount remain in waste beam.
    I'll try rest of wavelenght as soon as possible (at the moment i can't raise power of my ALC909, not enough current at home) and i'll search for a RF meter.
    Thank you very much.

    Andrew

  6. #6
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    Uhmmmmm....

    After tested pcoam parallel to supposed polarization (alc909-vertical), i've tried perpendicolar too.
    Well...not evident difference...and that's very strange.

    I've followed suggestions, with a blu square and a very slow scan rate, i can see zero and first order that pulse alternately, and when used a colour test pattern, the crystal work well. So i suppose to be in right way.
    But what about polarization ?

  7. #7
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    Hi Vega,

    Is it possible that the PCAOM (or LASER) polarisation is 45 degrees rotated from what you expect? That could explain why there is no difference when you try the PCAOM at 0 degrees (parallel) and 90 degrees (perpendicular).

    Kind regards,

    sonaluma

  8. #8
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    That is really possible ???

    I've never seen a pcaom mounted in a different way from vertical or orizzontal.
    No mirror in beam path, pcaom is in front of laser.
    Well...before to build a 360 panning mount and spend a lot of time, i'd like to know is it's possible a polarization at 45 and a easy method to discover that.

    Regards,

    Andrew

  9. #9
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    Hi Vega,

    This depends on the construction of your LASER head. If you have the specifications for the LASER head, this should state the polarisation. I have some LASER head with 45 degree polarisation from 3D display system.

    If you do not have the specification, some ways to test are comparing power or brightness using polarising filter with known direction (maybe compare using a LASER with known polarisation direction first, to find the orientation).

    Otherwise maybe you can carefully position the LASER head and PCAOM temporarily for testing, without making a permanent mount.

    Kind regards,

    sonaluma

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