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.
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Did you make this in Pyrex or Lead Glass?
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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.
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Commercial CO2 lasers use an electrode known as a Hochuli cathode with a gold and nickel catalyst to regenerate the gas.
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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.
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Steve
Qui habet Christos, habet Vitam!
I should have rented the space under my name for advertising.
When I still could have...