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Thread: Co2 Laser Re-Gas discussion

  1. #21
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    You missed the tip on H20.... It is what regenerates the gas in cheapies.
    You missed the tip on Xenon, it is needed for high power.
    You missed the tip on electrode processing,
    You need a tube oven.


    ~
    Yeah , I tried the go cheap with chop and pump on many gas lasers two decades ago... I learned. There is no such thing as cheap when there is 8760 hours in a year, and your client wants two years minimum.
    ~
    I spent three years working my way through college by often cleaning and rebuilding medical flowing gas co2s, and resealing the parts on Ebay. I've built my own Co2 tubes. I'll wager I have torn more commercial sealed tubes apart then you have ever seen tubes. My parts source was the largest reseller of medical gear in the Midwest. They had many brands of Co2 that I could pick up at 50$ a laser, because no one wanted an expensive commercial rebuild.
    I know this beast.
    ~
    If you value your reputation, do it right. If you go anywhere near a vacuum or physics conference (and there also was one shirt at SELEM this year) you will see T-Shirts that say "In VACUO VERITAS". (In Vacuum is Truth) It is a reference to how difficult it is to get vacuum and plasma devices right. Take the time to do it right because your customers will rat out a bad experience on the Internet in microseconds.
    This is not an easy industry.
    ~
    If you process a Hochuli cathode the way you would treat a Nickel cathode and vice versa your tube is dead, and both types are out there. BTDTGTS. Take the time to do it right and buy the gear.

    Steve
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  2. #22
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    That diffusion pump needs a Dry Ice cold trap or the oil vapor will seriously mess up the optics. Tubes need to be on station overnight.

    Steve
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  3. #23
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    Default thaks for all the tips

    Quote Originally Posted by mixedgas View Post
    You missed the tip on H20.... It is what regenerates the gas in cheapies.
    You missed the tip on Xenon, it is needed for high power.
    You missed the tip on electrode processing,
    You need a tube oven.


    ~
    Yeah , I tried the go cheap with chop and pump on many gas lasers two decades ago... I learned. There is no such thing as cheap when there is 8760 hours in a year, and your client wants two years minimum.
    ~
    I spent three years working my way through college by often cleaning and rebuilding medical flowing gas co2s, and resealing the parts on Ebay. I've built my own Co2 tubes. I'll wager I have torn more commercial sealed tubes apart then you have ever seen tubes. My parts source was the largest reseller of medical gear in the Midwest. They had many brands of Co2 that I could pick up at 50$ a laser, because no one wanted an expensive commercial rebuild.
    I know this beast.
    ~
    If you value your reputation, do it right. If you go anywhere near a vacuum or physics conference (and there also was one shirt at SELEM this year) you will see T-Shirts that say "In VACUO VERITAS". (In Vacuum is Truth) It is a reference to how difficult it is to get vacuum and plasma devices right. Take the time to do it right because your customers will rat out a bad experience on the Internet in microseconds.
    This is not an easy industry.
    ~
    If you process a Hochuli cathode the way you would treat a Nickel cathode and vice versa your tube is dead, and both types are out there. BTDTGTS. Take the time to do it right and buy the gear.

    Steve
    i skipped the oven since tube is not going to be at atm pressuere for more than 10 minutes,
    the difusion pump does have a cold trap that is running on a nitrogen cooler
    im totally un aware of the electrode processing needs, but since a tube is being refilled and not assembled from scratch i gess safe to skip for the moment,
    BTW my oldest refilled tube has been going on for a year now conserving its output power with only a 5watt loss (out of 100), on cheapy chinese tubes warranty is 6 months at most, and 3 months average
    so customers ARE happy with my work becouse i explicity tell them the output power obtained on the recharge, and at 50% the cost they dont care much for the power reduction, what they are convinced for is duration, and so far doing it for friends for almost a year and have no complaints on duration, actually the refilled tubes are lasting longer than the new ones, at expense of power loss i guess.

    if i could bup the power a little higher and keep the duration it would be worth all the efforts done

    Regards
    Ed.

  4. #24
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    Ten minutes up to air is an eternity if you have a cathode that uses a barium/calcium/strontium emitter layer. These are a "One Shot" cathode. They are a nickel or stainless cylinder with a layer of metallic carbonates coated on the inside of the cylinder. During processing the cathode is heated red hot in a reducing gas mixture to convert the carbonates to the pure metallic form that then bonds to the cathode. That tri-metal layer has a low work function which allows it to emit copious amounts of electrons when heated by the discharge. Exposing it to air at atmospheric pressure rapidly forms oxides which barely emit at all. This would not be my first choice for a quality tube but they are cheap, readily available because of neon and cold cathode lamps, and they work well. If the tube pressure is not correct they sputter metal which buries gas and ends up on the coolest part of the tube, which is the ballast or on the part with a neutral electric field, which is often the inside of the optics, making them slowly become more or less opaque.
    ~

    If you have a pure nickel cathode that acts as a catalyst to regenerate gas, you have to process it to strip the oxides off it. Usually done by baking in a hydrogen or forming gas furnace before assembly then cleaning with a hydrogen discharge or in some other proprietary gas mix. Having never processed one for a sealed tube, and having never learned the exact details of that secret second step, I have no idea how you would clean it in place. Sandpaper and baking in hydrogen (800'C) worked well on flowing gas tubes, but your electrodes are not removable.
    ~
    Aluminum cathodes are processed with a pure oxygen discharge at 2 to 5 mA per square centimeter, and the oxide forming process takes a day or two.
    Usually a second anode is used as it gets trashed by the oxygen..
    ~
    Hochuli and other alloy/oxide cathodes have their own techniques.
    ~

    Things that kill power: Sputtering of tube materials onto the optics. Mirror alignment. Hydrogen from the water vapor diffusing out of the tube walls . CO/CO2 balance in the tube. Poisoned or eroded catalyst layers. Formation of nitrogen oxide gases in the tube from a bad gas mixture.
    ~
    If I'm you:

    I'm going to try to find a cleaning mixture and a cathode processing mixture. Being aware that there is more then one type of cathode and that some tubes may have getters or catalysts that I might damage.
    ~
    I'd make sure I'm adding my .2% water vapor to the discharge. This is done perhaps, by taking a sorbent such as Molecular Sieve or activated charcoal powder, baking it under vacuum to free it of stored gases, soaking it in water, let it air dry, putting it in on a storage tube on station and backfill the storage tube with a little Co2. When you need your tiny amount of water vapor, you GENTLY heat the sieve causing the stored water to release as vapor when I crack open the needle valve. That gets monitored with a capacitance manometer. Make damn sure no dust from the sorbent gets back into the tube.
    ~
    I'm going to puff in some xenon to cool the discharge. I'm going to watch the sidelight spectrum at this point. Xenon is an expensive commodity.
    ~
    I'm going to bake the tube as much as I can to get "Crud" off the optics during pumping.
    ~
    I'm going to find a way to correct the CO/CO2 ratio, maybe by adding Co2. The correct ratio forms as the plasma runs for a few hours, so you cannot just puff in an excess co2 mix
    ~
    I'm going to open the tube in a glove box if I can. I'm going to seal directly to the 8250, 7720, or 7740 glass using a 8250, 7720, or 7740 tube, depending on what glass the Chinese used.
    ~
    If I have an RGA, I'm going to watch my gas mix.
    ~
    I might find a way to deposit very thin nickel or gold films or maybe a manganese dioxide film (pinkish) in contact with the plasma. One wag inserted nickel wire rings into the bore, but he was rebuilding tubes on a glass lathe. The best lasing is around the tube walls, so I'm not going to block the bore with a bulk catalyst.
    ~
    You have a heck of a lot of research to do.
    https://ntrs.nasa.gov/archive/nasa/c...9730020748.pdf
    http://www.repairfaq.org/sam/knapp/dksco2.pdf

    ~
    Thank my lucky stars I only have to deal with Krypton, Argon, mixes of the two, straightforward cathode processing under UHV, and a cleaning mix that adds helium or neon.
    I have to hit 1x10-8 or better for cathode activation and use a pinch seal, with NO oil, which is a whole different vacuum ball game, ie turbopump and Ion Pump. If I leave a mere fingerprint inside the manifold, I'm done for the day, however.


    Steve
    Last edited by mixedgas; 09-25-2018 at 08:58.
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  5. #25
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    You can watch him place the pre-processed electrode in the tube in this video. In the US that would be done in a glove box. The tubes coming out of the big metal boxes are the bake/burnoff vacuum oven step for removing "crud" from the glassblowing lab.
    ~
    https://www.youtube.com/watch?v=-0zYack5jUw
    ~
    See the fade/blink step, that is outgassing done so as to not crack the glass by overheating the electrode. YUK, NO oven.
    Looks like they flush in pure Helium, the purple evolving is Nitrogen outgassing from the tube walls. My guess is they are flow gas processing the tube.
    See how the white plasma moves on the cathode until it is hot enough and clean enough to fully activate? Done very slowly. When done right the plasma should be even across the inside of the electrode and very little plasma on the outside.
    Very cool, very clean, plant, thought....
    ~
    Steve
    Last edited by mixedgas; 09-25-2018 at 10:42.
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    Hey Steve;

    I've always wondered what the purpose of the Xenon gas is for in a CO2 laser. You mentioned that it helps with cooling.?. I thought that Helium was the best gas for that (high thermal conductivity). How does a huge atom like Xenon (especially when only present in trace amounts) help keep the tube cool?

    And a side question about CO2 tubes that are electrically excited - are the cathodes in those tubes similar in structure to what you'd find in an Argon laser? I would have assumed that the cathode filament in a CO2 tube could be smaller, since CO2 lases with much greater efficiency than your typical ion laser.

    Adam

  7. #27
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    Quote Originally Posted by buffo View Post
    Hey Steve;

    I've always wondered what the purpose of the Xenon gas is for in a CO2 laser. You mentioned that it helps with cooling.?. I thought that Helium was the best gas for that (high thermal conductivity). How does a huge atom like Xenon (especially when only present in trace amounts) help keep the tube cool?

    And a side question about CO2 tubes that are electrically excited - are the cathodes in those tubes similar in structure to what you'd find in an Argon laser? I would have assumed that the cathode filament in a CO2 tube could be smaller, since CO2 lases with much greater efficiency than your typical ion laser.

    Adam
    ~
    Xenon tempers or lowers the " electron temperature" of the gas mix, making it easier to pump the correct upper state of the nitrogen for best power transfer to the CO2. Basically lowers the electron velocity by collisions and reradiating the electrons. Helium is what actually gets the discharge heat out of the tube. Nitrogen serves to pump the CO and Co2 molecules to the upper lasing states by molecule to molecule transfer of what essentially pure heat in the form of molecular vibration. . Nitrogen gets very hot in a glow discharge compared to most gasses, in fact they add a trace of N2 to fluorescent lamps so they will heat up the mercury inside to run in winter.
    ~
    Xenon is helping tune the energy transfer in the plasma. it helps In creating the optimum N2 upper state for best energy transfer to the Co2. From what I just read, Xenon addition, done correctly kicks power up by as much as 10-15% in flowing gas lasers. Too much or too little Xenon lowers power. It also lowers the creation of N2O and NO which lower the output power in sealed tubes.(1) Forming N2O robs Oxygen from the Co2 molecules and does not disassociate in the plasma once formed, removing available CO2 from the tube and converting it to CO. Hence that whole CO2/CO balance thing lowering power when you seal the tube off is partially caused by N2O formation.
    ~
    Those are " Hollow cold cathodes" in the video intended to generate free electrons from just ion bombardment inside the cylinder and a high local electric field. They get mildly hot but do not glow red hot in operation like a thermionic cathode in a Ion laser. Same concept as a neon sign electrode. The current per unit area emitted is far smaller, compared to an Ion Laser Cathode. So yes, they can be small, but if they are too small they heat up and sputter metal/crack the glass. They will have some sort of emission coating on the inside.
    ~
    http://multimedia.3m.com/mws/media/9...data-sheet.pdf compare to https://www.egl-lighting.com/electrodes/
    ~
    Simple explanation: https://www.researchgate.net/post/is...Cathode_Effect
    ~
    (1) INFLUENCE OF XENON ON CO2 LASER PLASMAS
    Appl. Phys. Lett. 12, 289 (2003); https://doi.org/10.1063/1.1651996
    P. Bletzinger and A. Garscadden
    ~
    Steve
    Last edited by mixedgas; 09-25-2018 at 10:45.
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  8. #28
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    OK, I'm done for a while. This whole initial gas balance mess is why I will send my RF pumped tubes to a professional for re-gas, rather then do it myself. Time is money, and process development takes time and more money.
    ~
    BTW, Sinfocomp, never give away the final mix recipe or the fill pressures... It is too expensive to learn how to do all this stuff, to give it away.
    I read forum post after forum post on machining forums where folks just want to know the magic mix, put it with just a roughing pump, and skip the other steps. That can really bite you when you need your 15,000$ RF laser to work well with jobs on the line. I also know many RF lasers need critical adjustments to the exciter circuit when changing mixes. Hence the warning.
    ~
    I once ran a DC excited flowing gas tube on AR/Co2 only when out of mix just for a quick experiment. Only 10% of rated power at best, but it did lase. Leaking a little air in then raised the power to say 20% of rated. Nearly any co2 mix will lase, but there will always be an optimum mixture that you have to get RIGHT for the balance of lifetime and power.
    ~
    Steve
    Last edited by mixedgas; 09-25-2018 at 10:51.
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  9. #29
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    Default thanks for all the tips

    Quote Originally Posted by mixedgas View Post
    OK, I'm done for a while. This whole initial gas balance mess is why I will send my RF pumped tubes to a professional for re-gas, rather then do it myself. Time is money, and process development takes time and more money.
    ~
    BTW, Sinfocomp, never give away the final mix recipe or the fill pressures... It is too expensive to learn how to do all this stuff, to give it away.
    I read forum post after forum post on machining forums where folks just want to know the magic mix, put it with just a roughing pump, and skip the other steps. That can really bite you when you need your 15,000$ RF laser to work well with jobs on the line. I also know many RF lasers need critical adjustments to the exciter circuit when changing mixes. Hence the warning.
    ~
    I once ran a DC excited flowing gas tube on AR/Co2 only when out of mix just for a quick experiment. Only 10% of rated power at best, but it did lase. Leaking a little air in then raised the power to say 20% of rated. Nearly any co2 mix will lase, but there will always be an optimum mixture that you have to get RIGHT for the balance of lifetime and power.
    ~
    Steve
    i have invested weel over 2 years on this, and not giving up on it, i have found many incorrect ways of doing it, and if i keep trying i will eventually find the correct way.

    and each day that passes im one day closer to sucsess.

    Regards

    Ed.

  10. #30
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    Quote Originally Posted by sinfocomp View Post
    i have invested weel over 2 years on this, and not giving up on it, i have found many incorrect ways of doing it, and if i keep trying i will eventually find the correct way.

    and each day that passes im one day closer to sucsess.

    Regards

    Ed.
    Ed, let me know when you have all this copy-pasted and have grabbed the links. There is one post here I'd like to redact.

    Steve
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