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Thread: Help with Q-Switched fiber laser

  1. #1
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    Default Help with Q-Switched fiber laser

    Hi there,

    I'm trying to repair a marking laser at a friend's workshop, but so far some extra skills are needed, so looking for some expertise here.

    It's a Electrox Raptor 2, Enhanced Fiber Technology, with a Gooch & Housego MQC041-20Dc-FPS-24V RF driver and Q-Switch.

    Laser warning on the hood is saying 150W, 1064nm, 40mJ, 25-300ns pulse, but no idea about the typical values.

    Basically, the laser is lasing and engraving, but seems to lase only in CW and at a reduced power.
    Settings for the RF driver has no effect at all, I don't hear the typical noise of a pulsed laser and it engraves only on soft material (wood, leather etc).

    Seed pump diode current/voltage is approx 9A/5V when lasing.

    Even when I disconnect the RF connection to the Q-Switch, the engraving result is exactly the same so I suspect the RF driver may be defective ?
    Is there a simple way to check the RF driver, or to check anything else on the laser ?

    Any help appreciated, many thanks!

    Sebastien
    Attached Thumbnails Attached Thumbnails Pump diode + RF driver.jpg  

    cavity.jpg  

    Q-Switch.jpg  


  2. #2
    mixedgas's Avatar
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    Do you have access to an RF power meter capable of working at VHF and a 50-100 watt dummy load at 50 Ohms? An RF spectrum analyzer and sampler might help too.

    Else send the driver to Gooch in England.

    The modulator is subtractive, as you have guessed. So it will lase CW unless the AOM crystal is good and the RF driver works / is triggered.

    That driver has a first pulse suppression system, so the designers were worried about "Giant Pulsing" damaging cavity optics or the laser crystal if the Q-switch stuttered.

    Steve
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  3. #3
    mixedgas's Avatar
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    Gooch is amazingly supportive (at least in the US) call them and get a driver manual.

    Steve
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    Thanks Steve, no unfortunately I don't own a RF power meter nor spectrum analyzer, only a good multimeter - shame on me I know, I used to have access to a whole lab equipment at my former workplace but no more since I'm a full time laserist...

    Yes the driver has first pulse suppression, nice to learn that this feature was to prevent optics from melting rather than preventing a hot spot on the target being engraved.

    Ok will try to keep in touch with Gooch, was just afraid that they don't care much as a large manufacturer.
    The driver manual I already found it.

    You talk about lasing CW because modulator is subtractive - ok so assuming there is a problem with the RF driver not driving the modulator, is it relatively good sign that the laser is still lasing though only CW ? Does a missing driver impacts the CW power as well?

    Sebastien

  5. #5
    mixedgas's Avatar
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    If the crystal and or intracavity polarizer are properly aligned the laser should run at a CW power just slightly less then the Q-switched average power.

    One way to check the crystal is to carefully note it's alignment, remove it, and aim a HENE or polarized diode laser through it. You should see the beam deflect into an array of spots like a diffraction grating, or at least fly back and forth as you pulse the driver on or off.. May need to rotate the crystal by hand in a couple of different directions looking to the spots.

    If the cavity optics are properly peaked before removal, reinstalling the crystal and peaking it is usually easy.

    Steve
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