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Thread: Need help with HR mirror for CO2 laser.

  1. #1
    Join Date
    Mar 2016
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    Default Need help with HR mirror for CO2 laser.

    So currently I'm stuck on my CO2 laser build. I made the laser tube 1016 mm long with a 25 mm bore. I plan to have borosilicate electrodes on either side of the tube powered by one? 9 kv neon transformer. I have a extra 9 kv transformer (same model) I could use to power the other side if needed. My mirror mounts are made of 24/40 glass joints with a ~45 mm flange on the female 24/40 joint that will be connected to a washer with a oring in the middle. A similar setup to the one here.


    I can take a picture of my mount if that will help.

    Some things that are holding me up are that I'm unsure of curvature of the mirror I need for the HR side. I've read that 10 meters is preferable but am having trouble locating a source for a 25 mm mirror with a 10 m roc.
    I'm also unsure of the output coupler that I will need. Would this work fine?
    http://www.ebay.com/itm/25mm-10600nm...D_yaJ_DZFVEHnw

    Any help sourcing these parts would be greatly appreciated as well as any build advice. Building the glassware was the easy part, figuring out optics is proving to be much harder.

    I ran PSST and with my values it was stable but I'm still a little lost.

  2. #2
    mixedgas's Avatar
    mixedgas is offline Creaky Old Award Winning Bastard Technologist
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    Default

    Skip Ebay...

    Go right to

    http://www.laserresearch.net/

    Professional CO2 optics made by Meller Optics. You'll pay a little more, but you'll get what you specify.
    ~
    Then go download PSST! Software and run the cavity simulation based on the length between your optics mounts, and the radius of what you can buy.
    ~
    Calculate the radius and watch PSSTs indicated beam diameter. Yeah, a 10 meter and a flat will certainly lase for the right transmission, but it might not extract full power from your mode volume.
    ~
    Then determine your gain per meter for a typical flowing gas mix and calculate how much OC transmission you can safely have, then derate that transmission a bit, ie if you calculate a 15% T, buy a 10 to be safe.
    ~
    Don't rely on just the web site, talk to them on the phone... They may have some good advice for a new guy.
    ~

    I have one set new in the box for a 40-48" flowing gas CO2 if that fails. I've been holding onto them, but now can get sealed mirror systems if I need them.

    ~
    Steve
    Last edited by mixedgas; 04-05-2016 at 15:36.
    Qui habet Christos, habet Vitam!
    I should have rented the space under my name for advertising.
    When I still could have...

  3. #3
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    Mar 2016
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    Default

    Thanks Steve. That helps, I'll give laserresearch.net a call tomorrow and run PSST again after I have a idea on what radiuses are available.
    So for powering the laser will the neon electrodes work, or should I just use aluminium electrodes or something else possibly? I can seal wire through a piece of boro and connect that to a the electrode if that'd work better.
    I plan on mounting the electrodes like this.

    ...|.............|
    |---=====---|



    I'm a glassblower making the laser for a school project but I'm hoping to build something I can continue to use in future projects.

  4. #4
    mixedgas's Avatar
    mixedgas is offline Creaky Old Award Winning Bastard Technologist
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    The modern Neon electrodes will probably deliver chemical dust into your system if not processed at high current. There is a electron emissive layer inside the hollow cathode that needs activated to reduce the barium and calcium oxides to the electron emissive pure metal. For short term you should be fine, long term (weeks or more) that dust will crawl and sputter onto the optics.
    ~
    Did you make this in Pyrex or Lead Glass?
    ~
    As your probably using AC off the NST, you need a hollow cathode structure at both ends, traditionally this can be thin wall stainless steel (K&S Hobbies) or Nickel tubing. The neon electrodes classically use a Nickel tube. The Kovar in the glass to metal seals works fine as a low emissivity metal. Uncoated electrodes will have a higher voltage drop when running and will take more voltage (about 300V) to start the discharge. If you've found the rare, European, Pyrex neon electrodes you should also be fine.
    ~
    Commercial CO2 lasers use an electrode known as a Hochuli cathode with a gold and nickel catalyst to regenerate the gas.
    ~
    If this is for a kid's school science project I'll be glad to drop some glass to metal seals for Pyrex into the mail. If its lead glass I'd go with the neon electrodes.
    ~
    Steve
    Qui habet Christos, habet Vitam!
    I should have rented the space under my name for advertising.
    When I still could have...

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