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Breathing Life into a Vintage Gas Laser

Andrew Back
5
Open source (hardware and software!) advocate, Treasurer and Director of the Free and Open Source Silicon Foundation, organiser of Wuthering Bytes technology festival and founder of the Open Source Hardware User Group.

Comments

March 21, 2014 16:02

Back in high school I'd attempted to build an organic dye laser--Scientific American had just published an article on how to build one in their Amateur Scientist column. I got the high-voltage flash lamp to fire, but could never get it to lase. I suspect it was a problem with the mirror alignment, as I didn't really have a good way of doing that. Anyway, good luck!

0 Votes

March 18, 2014 01:34

Check the power supply transformer for any kind of hissing noise. Check the lead insulation. Recoat the mirrors using information from hobby telescope makers. Refill the tube using HVAC repair equipment. I guess the half mirror could have lost reflectivity over time.

0 Votes

March 17, 2014 15:51

Hi,

You could have a look at:- http://www.repairfaq.org/sam/laser/sp120opm.pdf

This is the instruction manual for your laser, and gives information on cleaning the mirrors, etc..

Good Luck,

Roger

0 Votes

March 17, 2014 14:58

I worked with one of these lasers when they were new. The power supply works just like one for a neon sign, although DC rather than AC. The point is, it's open circuit voltage is high enough to strike an arc in the gas tube. Then the supply drops into constant current mode and the voltage is determined by the impedance of the gas tube. So, what you see, 7KV open circuit, and much lower voltage, at constant current, is normal operation.

I would worry about the buzzing and shut down though. Overheating and protective shut down, perhaps.

The tube is glowing neon colored in your pictures, so I doubt if there is much oxygen in the gas. I think that would move the color toward the blue, but this is just a guess.

I had a smaller HeNe laser at one point that failed through Helium escape, and I would put that high on the list of likely causes. However, I am not sure there is enough helium in what you buy to fill balloons to do the job of soaking back into the tube. That tank has nitrogen, etc. in it to reduce the cost. Partial pressures at work here if your fill is not mostly helium? Again a guess.

Good hacking,

Charles

0 Votes

March 17, 2014 10:40

You could test the power supply by putting a dummy load on it and see how the power supply holds up. For a power supply of that age it is likely that all the electrolytic capacitors need changing.

Another possibility is the some of the high voltage insulation is breaking down. This could be just dirt or dust on the tube or the high voltage cabling. You could switch the unit on in a darkened room any high voltage break down may be obvious.

There was a article in the scientific American about 40 - 50 years ago that had article about making a HeNe gas laser from scratch but it did have a very comprehensive section on setting up the optics.

Good luck

Jeff

0 Votes

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