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Thread: Trying to revive an old argon laser

  1. #1
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    Default Trying to revive an old argon laser

    Last year I found this LGN503 russian argon laser that has a glass tube and is rated for 1W at 488nm line. This is a single line tunable version of the LGN502 laser that is multiline. So here wavelength can be switched by a prism on the rear of the laser. Unfortunately the tube appeared to be leaky, so I decided to try refilling it with fresh vacuum and argon. I've built the following vacuum station that has a rotary pump, an oil diffusion pump and a glass manifold with a valve, Pirani vacuum gauge, the second vacuum gauge filled with diffusion pump oil for measuring argon pressure when filling the laser tube and a couple of ports for connecting gas cylinders and laser tubes. Then I did the following:

    1) Pumped down the laser tube to the pressure <0.0001 Torr.
    2) De-gassed the getter by heating it orange-hot until it stoped emitting gases and vacuum became <0.0001 Torr.
    3) Slow heating of the filament from 0 to nominal 4V with 0.5V steps. Proceeding to the next step was at the moment when vacuum became less that 0.0001 Torr.
    4) Short-term overheating of the filament to 6.3V, for a couple of minutes.
    5) Powering off the filament and filling the tube with 1 Torr of argon.
    6) Powering on the getter to purify the argon fill.
    7) Trying to start the arc.

    So, the last step is unsuccessfull -- the arc does not start. Further research showed that the cathode has zero emission. I applied up to 6 kV between the cathodr and auxillary anode that is quite close to the cathode and the ammeter showed 0 mA of current. Where I could be wrong? Or the cathode is desperately dead?

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  2. #2
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    Does it double up as a vodka still?

  3. #3
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    Does it double up as a vodka still?
    Sorry, but what do you mean by such question?

  4. #4
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    OK, getter outgassed when activated for last step and poisoned the cathode...
    Your vacuum was not high enough for dispenser cathode activation. Quite simply, if you have rubber tubing on high side of vacuum station you will NEVER achieve good enough vacuum to activate cathode.
    ~
    Diffusion Pump oil residue will ruin the cathode surface unless trapped by dry ice or LN2.
    Your vacuum never was good enough.
    ~
    Try this, because the tube is not in an oven, it would outgas immediately on start anyways.
    ~
    This is not like a vacuum tube, getter is a NOT thing you want to run once you add the argon fill.
    ~
    Looks like nice version of BeO tube design invented by US Air Force and Dr. William Bridges right down to using SP magnet design.
    ~
    Following procedure is ONLY for tubes with external gas return and thin BeO bore. Using this on post 1969s tube designs will CERTAINLY kill the tube.
    ~
    EDIT!
    PROCEDURE REDACTED AFTER VEWING BY LASERBUILDER !
    EDIT


    ~
    Last edited by mixedgas; 08-17-2018 at 13:26.
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  5. #5
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    Thanks for a detailed answer. It will be cheaper and easier to find a working tube... You mentioned way too sophisticated equipment that I cannot afford.

    Also this tube has hard-welded mirrors instead of Brewster windows, so I'm not sure that coatings will survive heating.

  6. #6
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    I've done this at home before. I have full turbo, ion pump, cold traps, vacuum plasma isolator to protect pump, special PSU for cathode activation special tool to cold weld seals etc. It took seven years for me to work it out and get proper gear by scrounging when I was young. Best to find new tube. Ask JSC-Plasma if they have old one laying around you can have.
    I would have used special gas mix of krypton-helium-neon to clean tube interior. Doing my procdure to sealed mirror tube would kill it. You mind if I delete it? Would cause much damage to many tubes!

    NICE TRY!

    Best of Luck..

    Steve
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  7. #7
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    Ask JSC-Plasma if they have old one laying around you can have.
    Already done that. They don't have any NOS tubes for this type of laser, moreover, they don't work with private customers, only with companies and they don't even work with ukrainian customers at all. JSC Polyaron manufactured this lasers here in Ukraine, but it doesn't exist now. So the only possible way to get a tube is to look for it in the places that used these lasers, like university labs etc.

  8. #8
    mixedgas's Avatar
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    Sorry about that... If I send you small tube (And I Would!) I run risk of jail under US ITAR rules. Let me ask friend in Europe if she can help you...
    If you can hit 30 micron you can make a pulsed cold cathode tube with what you have in pumping station.


    Steve
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  9. #9
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    Thanks, I would be very grateful for any help.

  10. #10
    mixedgas's Avatar
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    Let me dig you up published documents on pulsed argon.. You may be able to re-use the optics.
    Steve
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