CO2 laser - Wilson Fabrication

In February of 2017, I thought it would be cool to build a CO2 laser. Keep in mind that I have no background in lasers, high voltage, or vacuum systems, and I was a junior in high school.

I’m now writing this in 2023, as I recently bought a real CO2 laser tube from eBay for $10 and have no real plans for it. Sometimes, you obsess over some technology that interests you for years, and when the technology eventually becomes cheap enough, you can finally buy it just to hold it in your hands.

Back in high school, one of my close friends, Brent, had recently gotten into glass blowing for his projects. He purchased an oxyacetylene torch head, two used supplementary nasal oxygen devices, a high-pressure pump, and an industrial oxygen tank. We would spend afternoons messing around with different projects. He was interested in building his own transistor from scratch and making scientific glassware, and I was having fun helping. That is until I decided I wanted to build a CO2 laser, and who can blame me? Isn’t every guy at least somewhat interested in burning things from a long distance? Unfortunately, today I no longer have the pictures of our first attempts, but I can tell you we used a borosilicate glass tube, used nails as electrodes, pulled a vacuum on the tube, and fed it with a neon sign transformer.

It did not work at all. The wavelength of light produced from a CO2 laser is absorbed by borosilicate glass, so even if it produced any laser radiation, there’s no chance it would have made its way out of the tube. And so, V2 was started.

I started with the glass from a fluorescent light, $50 worth of copper plumbing, and some steel brackets. The idea was that I was going to solder the copper pieces together and to one of the cast steel wall mount brackets. This bracket would house a rubber O-ring to seal it against the vacuum and a Zinc Selenide lens, which I could adjust its angle using 4 bolts clamping the bracket together. Zinc Selenide is one of the few materials that are optically transparent to the 10,600 nm light produced from the laser. On the other end of the glass tube, there would be a matching bracket which would house a mirror. In a CO2 laser, light only passes out one side of the tube, so you have to use a mirror reflective to the laser to bounce the light back through the gas and out the lens. This has the added benefit of encouraging more CO2 molecules to drop to a lower energy state and release their light in the same direction as the rest of the light.

Above, you can see these ends all soldered together. I added hose barbs to attach the vacuum pump and the CO2 canister. The copper tubes acted as a mirror/lens mount, gas ports, and the electrodes for the 10 +- 2kv arcs used to power the laser.

Fluorescent lights work by exciting the gas inside (Argon, Krypton, Mercury vapor, and others) to a higher energy state and then allowing these atoms to fall back to a neutral state. This energy is released as ultraviolet light, which is not visible to humans. A coating of phosphorus on the inside of the tube is hit by this UV light, which is then absorbed and re-emitted as visible light and heat. For fun, I wanted to see the CO2 arc inside, so I passed a small piece of sponge tied to a string through the glass to wipe away the phosphor coating.

As I’ve mentioned before, I used a neon sign transformer to power the laser. These transformers are terrifying; they put out 12,000 volts at 35 milliamps. That’s like elephant-killing territory. Who knows how I convinced my mom to let me build this in the garage. Anyways, the transformer was driven by a variac that I built myself. The best kinds of projects are the ones you have to complete to use as a tool for another project. Who better to narrate the whole setup than high school me.

That was actually one of the few views of V1 CO2 laser. As you can see, I used a home water filter as the pressure tank to hold the high-pressure CO2 that I got from airsoft gun CO2 canisters. These canisters sit at about 800 PSI, but once expanded to the volume of that tank, it sits at ~50 PSI. I would pre-fill the tank, pull a vacuum on the tube, and then flush all the oxygen out of the tube with CO2 and allow it to come back to a low vacuum pressure. At this point, I could slowly increase the supply voltage on the variac to about 10 kV, which would initiate an arc. Then I could dial the voltage down, as that amount of power really heated up the tube.

In order to test if I was actually producing any laser light, I used a PS3 eye camera. These are the joystick tracking cameras for the PlayStation 3, and at the time, they could be had for $5 on Amazon. I then removed the IR filter from the lens and aimed both the laser and camera at a wall to see if I could see a dot of light on the wall. And I could! Who knows if it was laser light or some other emission on the visible spectrum, but the “laser” produced something. Something I didn’t know at the time is the gas inside a CO2 laser is actually only a small portion CO2. Most commercial CO2 lasers are 10-20% CO2, 10-20% Nitrogen, and the remainder is helium. At the time of building this laser, I did not have the tools to properly mix gases at known ratios, but this is something I would love to revisit and try again someday. There are multiple types of gas lasers, and having the ability to switch between them and tune their emission by changing the gas would be a fun challenge.

Back to me winning a bid as the only bidder on an eBay listing for a real CO2 laser tube. Someday I hope to have a proper project for this thing. It would be cool to couple it to a fiber optic cable and attach it to a custom-built 3D printer or CNC machine. But, as I’ve mentioned, 10,600 nm doesn’t play well with glass, so some fancy hollow-core fiber would be required. For now, it’ll live as a nice piece of wall art.