Homemade CO2 laser

This has been an ongoing project for about 3 or 4 months now, it's part of my A levels and has so far been a huge learning curve, I feel I'm slowly getting there finally, despite the hefty set back of a burnt out transformer flyback transformer yesterday! The laser tube is 40cm between electrodes, 60cm between mirrors and has a bore of 11mm. The HR is plane, and the OC is zinc selenide of unknown splitting ratio. I won 4 beam splitters, 4 lenses and a mirror all for 10.6 microns on ebay for £50, and thankfully CO2 lasers aren't too picky about OC reflectivity so it should still work. The optics were an absolute bargain, the beam splitters are 35mm, as are two of the lenses and the mirror, so a lot of pricey germanium and zinc selenide. I machined the mirror mounts myself, and they have an acrylic mirror holder to take the strain off the optics when adjusting the mirrors, and to maintain adjustment when replacing the optics. The cooling pump will be an aquarium pump, and the gas supply is going to be a mixture of He, N2 and CO2 fed through a needle valve and out via a vacuum pump. I now need to sort out a power supply, rig up the gas supply, align the mirrors and I should hopefully be lasing.

Forums / High Voltage / Winding a flyback secondary - 4hv.org that's the transformer I had going until yesterday

And here are a few pictures of my progress so far, any advice, questions or neon sign transformers are very welcome!

Nice! I've run my 40W tube from a 30kV 25mA NST before, and it works just fine, even unrectified. Good luck with your project, those optics were a steal!

Thanks! Oh I know they were, I was considering spending £50 on a tiny ZnSe output coupler and about £100 on a concave HR, then this lot came up on ebay and I just had to have them! The focussing lens should be useful as well. If the plane high reflector makes aligning a pain I'll either grind a concave one or sell some of my optics to buy a new concave one.

Nice work HD,

Where abouts in the world are you? I have quite a few HV laser supplies kicking round that I don't need. I also have some dead tubes that have perfect mirrors and couplers in them that could be smashed and scavenged

You going for a flowing gas? Dam I love seeing this kind of stuff, reminds me of my Uni days.

cheers

Dave

Thanks Spooky, I'm in Bath so not far from you in fact. That sounds very interesting! Are those the sealed chinese tubes? I've heard they haven't got the best lifetime, it still amazes me how cheaply a 10watt plus tube can be made and sold for!

Yep flowing gas, picked up a vacuum pump on trade it a while ago, I'm planning on going down a very similar route to Jarrod Kinsey here Jarrod's Laser World: First CO2 Laser for the gas. Now just looking for a beefy power supply as my flyback has failed, I've put up a request for a neon sign transformer on 4HV, the postage seems to be the killer as all the best stuff is on the other side f the world! What kind of supplies do you have?

I've got a few in the 25 to 28 Kv range from laser cutters that I don't use any more

Mostly Japanese PWM stuff if that is any good to you?

The Chinese tubes are getting better, the ZX EFR series are up to 15,000 hrs now and fast catching up with the RF units that costs 30x as much
On my last visit to China I went to one of the factories, health and safety? whats that...the pay rates are silly levels of tiny and everything is focussed on price. I was surprised to find most of the glass tube makers still hand blow the tubes!!

If you need something lower powered what about a non PWM from China?

Your only 30 minutes away

cheers

Dave

Indeed, although I don't think CO2 lasers are mass produced enough to be worth a custom machine to manufacture them. Cheaper just to pay workers peanuts to hand make them. Would be an interesting process to watch for sure.

Also, to add on to the NST thing above, it's not the best way to drive them, however it wouldn't matter too much in your case. Reason being is the sealed CO2 tubes have return paths for the gas, allowing it to circulate through the tube, react with the catalyst to combine it back into CO2 and then back into the bore, but yours doesn't have that.

The regular tubes operate DC, which helps push the gas around the system, whereas with AC there isn't really any driving force, so you may notice a slight decline in power in a sealed tube over a short time.

In your case with flowing gas though, AC or DC doesn't matter as much.

That should be plenty voltage! What current do they supply, and I assume they are constant current sources? And can I adjust the voltage to the needs of my tube?
I imagine that'll certainly work, what kind of money would you be asking? I was looking for a neon sign transformer to put on one end of my variac, that's what most people seem to do but if you're happy to part with one of your power supplies for not too much that'd be great.

Yeah I can imagine the factories are like hell to work in, but what can you expect with those prices!

Looking on ebay they are still a bit pricey for me, especially considering the ridiculous postage they put on them.


Hi Things,

I've got 200 1kv diodes I need to solder into a bridge rectifier at some point, I know that DC operation also allows you to exhaust any stuff sputtering from the electrodes a bit more easily too, but AC operation should be alright. I just like the idea of an NST for reliability.

Thanks

I think a nice Co2 is next on my list, so any parts donations gratefully accepted

I'll dig out the old ones guys, free....they are just literally kicking around from upgrades so no real use to me. I still have some tubes with life left in them too but in the job I'm in consistent power is paramount so a half life tube isn't much good to me. (a 90 watt tube putting out 70 watts is effectively dead for what I'm doing as it may mean hours of modifying power / speed settings on different jobs)

I know very little to nothing about the electronics inside them, Physics and Lasers (resonator onwards) is my speciality but electronics is well above my pay grade.

From memory the voltage isn't adjustable but the current is. (getting anything info wise from Japan or China about how they work is dam near impossible)

cheers

Dave

That would be fantastic, I'll see if I can get my dad to give me a lift to yours soon if that's ok? And have a look at what you've got when it comes to the tubes, I could be well be interested in salvage or a worn out one of those too... and I'll definitely have one of those power supplies! I'll try and get it done before all my university application hots up and gets serious.

Thanks so much, I was absolutely gutted when my power supply burnt out.


Henry

Hiya Henry,

Sure no problem, gimme a week or so to get on top of this weeks workload and I'll get them sorted for you I can always drop over there if you are transportless, I go to Jennor Timber quite a lot for supplies so right in your backyard I think I have an 80 watt supply and half life 80 watt tube here somewhere that just needs connecting up.

cheers

Dave

Dave@opticalpower.co.uk and my works phone is 07429149371

Great, just emailed and PMed you, thank you very much for this.

Found the tube, Bejing EFR F2 80 watt, just gotta find the matching supply now.

Its about 5 feet long Henry, I have some mounts here somewhere as well.

cheers

Dave

That's great thanks, I' have space to keep it till I feel like having a closer look, testing it and possibly acquiring some optics. My father runs a small engineering operation and we're planning on a workshop rebuild soon so we may even set it up with an X Y table, the mounts could be useful! I've looked up similar ones and the supply shuld be great for my project, I'm right in saying it has terminals at the back for controlling the output?

I'm right in saying it has terminals at the back for controlling the output?

Click to expand...

I'll take a look in the morning, most of the connections on the PSU are for step controllers or such like, theres a TTL connection as well as a host of other screw terminals for various machine functions but I swap out like for like on those so never really got involved in what they actually do (my skills with electronics really are basic)

cheers

Dave