An impatient and curious question about chinese laser tubes

[Greg Facer]

AS some of you might know, I have a Shenhui that originally came with a 150w RECI. That original tube was arcing to the frame much too easily, and it was recommended by Shenhui, Reci, and many here that get a warranty replacement. So, I did.....problem is that that replacement arrived broken....and the 2nd replacement arrived even more broken (but packed better, go figure).

Leading me back to replacement #1. On that tube, the break is right where the little coil is, as shown.

So my question is....what does that coil actually do? It isn't cooling related, and it seems to be a link from the outer gas reservoir to the inner laser tube. I know this for sure as I have the first tube with the ends broken off as RECI asked me too, so I could feel where the tubes met up. I have two possible theories. One is that the length of the glass coil insures that the arc of the laser voltage only wants to stay in the center tube. The second is that it is for preventing condensation from entering into the active laser section.

I am tempted to mount this tube and see what happens. Obviously, if the purpose of the tube is the first theory that would be a *bad* idea. If it's just condensation, should work fine (at least in short bursts). Any ideas?

(I just measured / guessed the length of the coil if it was extended, and it's a little longer than the lasering tube....hmm, time to see if anyone else knows the actual answer)


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[Nick Foley]

When installing my 90W RECI recently, I was very curious about this as well. Your theory about preventing arcing is interesting. I could see that being correct.

In other uses though, coils are frequently used as heat exchangers- maybe the purpose of the coil is to ensure that the CO2 moving in to the inner tube becomes the same temperature as the inner tube itself.

[Rich Harman]

I don't know but my guess is that the purpose of the coils is to aid in circulation of the gasses. A break like yours could mean that the gasses stagnate in the central portion of the tube.

[George Carlson]

The laser tube has a mixture of gasses in it at very low pressure (vacuum). For the laser to operate, the gas must be cool. In the original CO2 lasers, they used a high pressure cylinder that leaked fresh gas into the tube while a vacuum pump pumped out the old. Now we use sealed CO2 lasers. The outer envelope on the Chinese tubes is a gas reserve. The actual laser is the very small tube in the center. The coil acts as a pump to pump cool gas from the outer resovoir through the center laser tube. There is another tube surrounding the laser tube, that's the water jacket. The glass work in these tubes is truely amazing.