co2 tube problems

[nitrous]

Thanks for your thoughts.
So, is it fair to say that He loss is a major contributor to short tube life in cheap laser tubes?

I've read recently about refillable CO2 lasers. They have a resealable fill tube that is easily accessed for evacuation/filling of gas.
It looks like they fill to an "optimum pressure" by monitoring the laser power output.

I wonder if this is a compromise between flowing gas and a sealed tube type laser?

Nitrous

[mixedgas]

No, the refill valve is there to adjust pressure and remove impurities and degraded mix. There is a bit more to it then just pumping down and refilling, there are bake-out steps to remove contaminants on better lasers, etc.

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In all gas lasers the gas circulates due to thermal and electrical effects. For a HENE or RF CO2, the flow is marginal, for an Argon its really fast, requiring return paths built into the tube, and for a flowing gas Industrial CO2, its rock and roll. The magnitude of that flow level is beyond the scope of this discussion.
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In a flowing gas laser, the gas is really moving, either straight to a vacuum pump, or in much larger lasers, through a sealed pump called a Roots Blower and into a heat exchanger to avoid wasting expensive gas. Laser grade gasses are purity certified and are not inexpensive. Xenon is about 700$ a bottle for a D2 size these days.
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The goal is two fold, very hot gas does not lase well, and fresh gas is not degraded by high energy densities.
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How that is balanced against different models of laser is beyond the scope of this discussion and requires a trip to your nearest university library or internet with a good laser physics book.
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Steve

[nitrous]

Perhaps I should have put in a link to the system I was talking about.
These tubes are just evacuated and filled - multiple times.

https://www.youtube.com/watch?v=_EjXaSnyATM

I hope this link makes it.

Nitrous

[Laser Wizardry]

" 15 characters"

[swamidog]

stop! you're making the free-trial sized laser cutter in my garage sad and jealous.

Can't Resist... Industrial CO2 laser porn. I loved hearing these turbofans spool up in the morning to get that gas flowing between the 4' long electrodes... Almost as much as as I loved watching it cut half inch steel plate at a feedrate of 26 inches per minute......

http://www.laserwizardry.com/mitz.jpg
http://www.laserwizardry.com/mitz2.jpg

[mixedgas]

Perhaps I should have put in a link to the system I was talking about.
These tubes are just evacuated and filled - multiple times.

https://www.youtube.com/watch?v=_EjXaSnyATM

I hope this link makes it.

Nitrous

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Having worked with lasers for years, and done plasma tubes for years, I can tell you much about this. If the difference between my laser working and not working was a copy of an ACE Glass 8192-209 valve with high leak rates, I would not be purchasing that system. I would use all metal valve actuator type mechanisms, or a pinch seal, both of which I have used before, and have the tooling for.
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They also do not bake the tube out under vacuum to drive off water vapor, they only had it at high vacuum for a few minutes, they do not use a heavy flushing gas, no cathode cleaning gas mixture, etc.. I could go on and on about what that does to tube reliability.
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Also for a 150 watt tube, those optics are WAY too close to the plasma discharge for my comfort.
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With respect,
If you think that video shows you how to do a reliable tube refill, well, ROFLOL. It shows you a very simple refill process that we might use in a teaching lab here at the university. I use a proprietary mix of heavy inert gasses to clean tubes while they are running.
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At least they did use a turbo-pump instead of just a roughing pump. But the pump is so far from the tube its pump rate is very limited.
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This is a credible tube refiller for CO2 lasers, and note what he says about Chinese lasers in his rant section:
http://www.parallax-tech.com/services.htm
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That valve and O-ring seal has a heck of a high leak rate for the task at hand. You will be pumping that tube WEEKLY!
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See:

http://www.parallax-tech.com/hardsea...m/hardseal.htm

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Steve

[nitrous]

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Having worked with lasers for years, and done plasma tubes for years, I can tell you much about this. If the difference between my laser working and not working was a copy of an ACE Glass 8192-209 valve with high leak rates, I would not be purchasing that system. I would use all metal valve actuator type mechanisms, or a pinch seal, both of which I have used before, and have the tooling for.
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They also do not bake the tube out under vacuum to drive off water vapor, they only had it at high vacuum for a few minutes, they do not use a heavy flushing gas, no cathode cleaning gas mixture, etc.. I could go on and on about what that does to tube reliability.
.
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Also for a 150 watt tube, those optics are WAY too close to the plasma discharge for my comfort.
.
.
With respect,
If you think that video shows you how to do a reliable tube refill, well, ROFLOL. It shows you a very simple refill process that we might use in a teaching lab here at the university. I use a proprietary mix of heavy inert gasses to clean tubes while they are running.
.
At least they did use a turbo-pump instead of just a roughing pump.
.
This is a credible tube refiller for CO2 lasers, and note what he says about Chinese lasers in his rant section:
http://www.parallax-tech.com/services.htm
.
.
That valve and O-ring seal has a heck of a high leak rate for the task at hand. You will be pumping that tube WEEKLY!

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Steve

wow, I really wished you hadn't replied.
There is absolutely no respect in your post whatsoever., but I think you knew that when you posted it.

I spent much of my career prior to medicine in a research lab. Not a laser lab, but a physical chemistry lab doing dielectric relaxation studies in glassy systems. Yes, it was at a university.

If I had responded to a question like you did, even my most junior undergrad students would have challenged me with all the conclusions I jumped to in reviewing that video. I won't go into the obvious ones. I hope someone else will.

Take care,

nitrous

[Laser Wizardry]

" 15 characters"

[mixedgas]

If you want to find out about plasma interactions in the tube while sealed and running in the initial gas mix, you would need to start with references in Hochuli's works. Then find works by Anthony DeMaria and Thomas Hennessey. That is outside of my scope, as I build them, fix them, and apply the technology to research and commercial ventures. However I have worked on medical 60 watt DC flowing gas, and sealed systems, including the glasswork. I've used systems for cutting and engraving to 400 watts. I have re-processed Ion Laser and CO2 Laser tubes.
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I take pride in my fine care of the students I encounter with respect to patience and learning.
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Basic laser rate equation and design is covered by Silfvast. . Find 2nd Edition if possible.
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http://www.creol.ucf.edu/Research/Publications/3613.pdf
ISBN 10: 0521833450 ⁄ISBN 13: 9780521833455
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Slifvast, William Laser Fundamentals, Cambridge University Press, 2004.
ISBN 10: 0521833450 ⁄ISBN 13: 9780521833455
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Dr. Silfvast is the inventor of a whole class of gas lasers, and his book is a good mix of theory and practice.
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My apologies, its rare we get a deep plasma physics and vacuum technology discussion around here.
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Ok, I'm trying to think of Socratic questions, so here goes.
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You be the student two years into your plasma physics masters, Doctor? Based on your linked video...
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What are the ramifications of the fill valve being located on a long, narrow, tube to the vacuum station with respect to pumping rate and ultimate vacuum?
Why does this affect plasma lifetime?
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Please research the specified leak rate of a PTFE sealed valve in high vacuum service? How does the narrow aperture affect pumping speed and ultimate tube cleanliness?
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With respect to the initial pump-down as shown in the video. At what pressure range will laminar flow cease and turbulent flow take over? When turbulent flow has also ceased, if the plasma tube was instantly isolated from the vacuum station, lets discuss how we would estimate the percentage of old gas remaining in the tube, if the tube had a volume of 500 mL and the design fill pressure was 30 Torr of standard laser mix?
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If a slight leak occurred at the O-ring seal to the pump manifold, how would we detect it, given the equipment in the video? Since Air contains at least three of the constituents active as ions or neutral species in the laser plasma, can we detect a leak by viewing the visible optical spectra? Make an argument for or against that technique. Why would a professional tube re-processor own a helium leak detector?
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Why would I have a flowing gas other then laser mixture or air gently flowing down the vacuum manifold when I connected the manifold to the refill valve? Why would initial connections to the tube normally be made in a glove box?
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Based on Hochuli's 1970s work, why would we add or avoid adding trace amounts of water vapor to the plasma?
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Would the water vapor in the room air in the video settle on the plasma activated glass surfaces in the tube?
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Can we discuss three physical or chemical processes that retain undesired materials on or in the tube wall?
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Which orbital is bonded during a pinch compression seal of a copper tube used as a vacuum fill stem? Is this an improvement over a flame seal or valve?
Once we have solved the problems related to the construction of the vacuum manifold, How could we accelerate pumping of containments remaining in the tube ? What is the physical limiting factor in the tube construction for the amount of heat or cooling we could apply?
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Which rare gas, based on first principles, would be the best for removing residual water and organics from the plasma tube bore during the initial bombardment? Why would I use a mixture of 8:1:1 Argon, Neon, Helium to plasma clean the tube walls before admitting new gas? (Not the mix I was taught to use, but close enough for discussion)
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A rote memory question for you? What is the commonly accepted current density per unit area of cathode when using oxygen plasma for initially activating an aluminum cold cathode? What damage could the oxygen plasma do to other tube electrodes? What are the signs of an improperly processed cathode?
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How does a Epoxy Seal exposed to plasma degrade the interior of the tube? What materials are released? There is a common type of epoxy used for long term sealing of plasma tubes, what does it contain that reduces its leak rate, reduces helium diffusion, and makes it resistant to indirect plasma? How long did early soft sealed helium neon laser tubes last?
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What are the variables in creating a successful partial hard seal using indium-gold alloy bonding for a GaAs laser mirror to pyrex glass?
What is the expansion co-efficient of Kovar? How can I tell visually if Kovar is well sealed to pyrex glass?
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You come across a heavily oxidized piece of metal sealed to an unknown type of glass. The joint is not mousey grey, but a shade of orange. Do you have an idea of what alloy is sealed to the glass? Name the probable coefficient of expansion of the glass. Is this glass less permeable to helium then borosilicates?
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You can view this as me showing off, or me starting a serious discussion, please pick one. There are some areas of which I am under a previous NDA, and will refrain from discussing with respect to tube processing techniques.
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Shall we make amends and discuss? Please be aware that this will take a long while. I am currently responsible for a whole college department's technology support with respect to new equipment and repairs. They have not had a budget for an electronics technician for eight years, so I am busy.
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The double dots are placeholder spacers, because this forum software shows the text collapsed on my machine.
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Please watch this video of a reasonably serious Chinese laser manufacturer showing you a carefully edited view of their tube processing. Note they do have hard sealed tube junctions but possibly not hard sealed mirrors, in their top line of tubes.

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Please note the details of the processing stations, although much of what I would look for is hidden..
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https://www.youtube.com/watch?v=tYDHQ_mH1Bc

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I need to go wire 42 thermocouples on a three story undergraduate distillation column, and my next reply will be after the veteran's day holiday.
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Steve

[nitrous]

You know, I wondered if you're response was that of a burnt out academic who had lost his passion for teaching...or a disgruntled tech who "learned it all on the job" and knows more than those self important academics with all that useless book learning.

Your response says it all.

Please don't waste any more of your time with me. It's obviously far more important than that.
Make no mistake. I know a good tech is worth their weight in gold but a great tech doesn't waste their time getting into pissing matches with academics. There is never a win for anyone there. But you likely already know that. I'm sure you've heard this many times before. ��

Take care,
Nitrous