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Thread: DPSS laser crystal quesion?

  1. #1
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    Default DPSS laser crystal quesion?

    I was messing around with my older Crystalaser branded heads, in the last month I have two dire for different reasons and playing around with them I found the crystal assembly at fault, it outputs a very dim multi mode beam, I confirmed it was that section as I put that into a different head and had the same problem so I used it's pump diode to fix the other head. but I am wondering why it failed like that, what goes bad with the crystals on a laser that only outputs 25mw?
    Can the crystals be visually inspected for this?

    I don't know the power of the pump as I have no data on it, looks like a C-mount but the beam is inline with the mount and screw

    Thanks
    Polk SDA SRS, Parasound HCA 3500, Luxman M117, Onkyo 504, 7.62X39, sometimes a ball on a string is the greatest of toys for us nonhuman types. oh and some lasers, lots of lasers

  2. #2
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    Id bet the coatings got damaged. Maybe water maybe the pump diode. Maybe heat. If all it does is 25mw unless its an exotic wavelength Id just toss it. It could a damaged pump diode too.

  3. #3
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    mixedgas is offline Creaky Old Award Winning Bastard Technologist
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    Low power DPSS often use a Vandate/KTP or Vandate/LBO bonded crystal assembly that is very thin, a fraction of a millimeter thick. While self aligning and often having the mirror coatings on both sides of the assembly, thermal shock caused by the pump 808 beam often debonds the crystals. They also die from optical coating damage or internal optical damage from the pump diode being too tightly focused.
    ~
    Good ones are contact bonded, they are polished so smooth that the crystals fuse togther on contact, under modest pressure. The best ones are possibly diffusion bonded, but that would not be the case in a low cost laser. Low cost ones are often glued together. Either way, the materials have slightly different coefficients of expansion and thus can break apart from mechanical, optical, or thermal stress.
    ~
    You can usually get the raw bonded crystal for a 50 mW or less greenie on Ebay for 19.95 and shipping. They have to be oriented to match the pump beam polarization, and you have to be careful where you put the focused pump beam spot. Obviously its best if its in the Vandate or YAG and not in the KTP side. Overdriving cracks them quickly.
    ~
    These assemblies are for ease of manufacture, the sides are so close together that cavity alignment is not needed, or they are coated to need just one external output coupler mirror...
    Without this sort of thing there would be no 19,95$ green pointers..
    ~
    Steve
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  4. #4
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    I’d still check the pump diode first. What makes you think the crystal has an issue? The fact that the output
    Is all multimode and stuff is what makes me think pump diode. Steve’s dead on but I’d check that first before ripp8ng the crystal out. Though I doubt there would be any output with messed up pump since it can’t couple right. Worth looking at first. Prob have to remove pump to get to crystal anyway.

    Never mind I see you already looked at the pump. Tried to delete post but it didn’t

  5. #5
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    thanks for the info, I need to put the crystal under some magnification, was also wondering what would be a ball park number for the efficiency the 532nm lasers get? is 10% total too optimistic?
    Polk SDA SRS, Parasound HCA 3500, Luxman M117, Onkyo 504, 7.62X39, sometimes a ball on a string is the greatest of toys for us nonhuman types. oh and some lasers, lots of lasers

  6. #6
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    I looked at the crystal assembly under my microscope and I am indeed seeing what looks like a bonding failure and discoloration. what is odd on these is there is a square window and the crystals bonded to that like a sandwich with the glass in the middle, the substrate the crystals are bonded to is bonded to a copper block so they are suspended in the middle and all of that and is stuck to a TEC, the small postage stamp size little ones that I can't seem to find, so that will get dunked in epoxy remover to harvest the TEC.

    The reason for the efficacy question is I lack a meter precise enough to calculate that number.
    I have another laser that's 200mw and needs a diode and am unsure on what wattage pump I should get for it

    Thanks again for the help
    Draco
    Polk SDA SRS, Parasound HCA 3500, Luxman M117, Onkyo 504, 7.62X39, sometimes a ball on a string is the greatest of toys for us nonhuman types. oh and some lasers, lots of lasers

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