Welcome to Laser Pointer Forums - discuss green laser pointers, blue laser pointers, and all types of lasers

LPF Donation via Stripe | LPF Donation - Other Methods

Links below open in new window

ArcticMyst Security by Avery

Multiple electrodes to minimize voltage requirement

twelti

Member
Joined
Jan 3, 2019
Messages
40
Points
8
I'm interested in learning more about CO2 lasers. I would love to eventually build one. It's more of a thought process right now, I'm still learning about lasers in general. I'd be interested in a 80 + watt device (maybe start with a smaller one to learn on). I'd love to use a design that minimized voltage and length requirements. So I understand that it is possible to use more than one anode and one cathode, thereby minimizing required total voltage. I'm guessing there is a trade-off then? Is there some reason one could not have, say, a series of alternating electrodes, spaced so they don't arc, and then have a very much smaller required voltage?

Also, is it possible to fold the tube up into several shorter lengths, perhaps combined with the above multi-electrode approach? I did see reference to this idea in a book I have been reading. I'm guessing though, that the additional complications in construction, additional mirrors, and alignment would make it difficult. It is interesting to think about though...
 





Anthony P

Well-known member
Joined
Oct 7, 2018
Messages
529
Points
63
I have built several homemade CO2 lasers over the years. Among homebuilt lasers they are probably the easiest to get working. They are very forgiving of vacuum leaks and misalignment. There is a ton of information on SAM'S LASER FAQ. As you said, start with a simple design then expand. Some tips right off: Plan ahead so that parts can be re-used in future builds. Good vacuum system is worth investment, but ordinary pumps used for HVAC work great, valves and fittings are more important. Use a HR/OC combo, don,t waste time with polishing salt crystals.
Current is key to higher power, voltage needs to be high enough for stable discharge but power comes from current density. Also, get premixed gas. This will greatly simplify construction at least to start. Fat o-rings for adjustable mirror mounts work great. If you plan to use neon sign electrodes start looking for those now, as they are hard to come by in Pyrex in the USA.

I recently shelved the last of my scratch built CO2s for the prefabbed sealed tubes widely available now. It was soooo easy, but that's a Betty Crocker build. I look forward to hearing more about your progress and would be happy to help if I can.
 

twelti

Member
Joined
Jan 3, 2019
Messages
40
Points
8
Thanks for the advice! I would love to benefit from your real world experience. But what do you think about having more electrodes? I'm guessing it won't be a good idea especially given your comment about hard to find electrodes. I though people were using cheap metal fittings for that. I guess the electrodes are better (less sputtering etc.)?
 

Anthony P

Well-known member
Joined
Oct 7, 2018
Messages
529
Points
63
You are right, neon electrodes are not absolutely necessary. They do solve a lot of problems like keeping discharge away from mirrors or o-rings. A folded resonator is a very viable design. In essence it combines 2 discharge tubes in series. Using 4 electrodes in this configuration is workable. If running DC, Just place both - electrodes near folded end and + at HR and OC ends. If using AC just make sure both transformers are in proper phase with each other. In my experience AC works best. DC will cause heating at anode and then there is the rectifier to add to the mix. There are those who will argue that maximum power and efficiency come from DC but I have not seen this in experiments.

Again, I suggest a simple single bore set up to start with. Then you make it a complex as you like. Also, if all you want is an 80 watt laser, these can be bought "off the shelf" for the same money or less than home-built.
Gotta work now... talk later.
 

twelti

Member
Joined
Jan 3, 2019
Messages
40
Points
8
Very interesting about the AC. I also had heard DC was better. I like the AC also since no rectifiers or nasty capacitors! Relatively safer and simpler. Just the NST. Yes, it seems you can buy a 50w tube and matching power supply for around $300. I was wanting to make it from scratch, but yes, i could start with a prefeb tube just to get my feet wet.

When I was a boy, I bought one of those and played with it. Did all sorts of crazy stuff, like grounding one end and burning ants with the other. Seems like I'm luck I didn't fry myself.
 

Anthony P

Well-known member
Joined
Oct 7, 2018
Messages
529
Points
63
Sorry for misunderstanding. I did not mean to use a prefab tube, I meant to keep the first scratch built very simple in design. I would not go straight for a folded resonator design until you have got the hang of a single straight tube. Same goes for multiple electrodes. Whether you use neon sign electrodes (NSE) or use the metal fittings as electrodes there a things to learn. Such as the fact that your vacuum line is going to act as an Earth ground. There are parts that may unexpectedly become electrified. High voltage seems to have a mind of its own sometimes.There can be static build ups and wire insulation can fail even if it's rated for double what you are sending through it. Could go on and on.

I am all for scratch built! The prefab tubes take all the fun out of it. I am just saying start with a simple, straight axial flow device. Gain high voltage, gas, alignment and vacuum experience, and then go for something more complicated. Last year I scratch built an argon ion laser similar to the Scientific American design. Just bore sighting the alignment laser took weeks ( trying to get a 2+mm laser beam to shine perfectly down a 1.75mm bore). Scratch built is difficult and frustrating... but it is also very rewarding when you get that first light from your work.
Also, I may have some parts I'd be willing to part with.
 

twelti

Member
Joined
Jan 3, 2019
Messages
40
Points
8
Regarding the HV twitchiness, is it possible to use a high voltage probe to check to see which parts are "hot"? Of course, if it is intermittent...

I'm just trying to think of how I would design it so there is no need to get anywhere near it when operating. I guess you would need to when adjusting the optics though. Or do you only adjust the optics when using a separate alignment laser?

Perhaps I can pm you if/when I'm collecting parts, so see if there is anything you want to sell. Cheers.
 

Anthony P

Well-known member
Joined
Oct 7, 2018
Messages
529
Points
63
Common sense is first line of defense with HV safety. A voltage divider probe is cheap and easy to build. A neon idicator light attached to ground wire is helpful. Never touch anything metal on the device when powered even if it is not part of the electrical system. Ground power supply. Volts jolts, but mills kills. If you accidentally brush up against a hot part it probably won't kill you but it will make you spit out your chewing gum.LOL. Mirror alignment can be done with power off. I still use allen wrenches attached to wooden dowels.
Do you have any drawings of your design?
 

twelti

Member
Joined
Jan 3, 2019
Messages
40
Points
8
Good advice! Your "Volts jolts.." reminds me of some of the mnemonics I learned in school (BSEE). I should know most of this, but it has been over 30 years. Since I have been in acoustics, I rarely had occasion to think about volts, mills, divider etc. But it is coming back.

I was thinking about getting a HV screw driver, or make one as you did.

No dwgs yet, I'm still considering general options. I really like the AC only idea. Unlikely anything is going to get charged up. even so, I think I will make it with an insulating, IR blocking screen around it, like in the S.A. article, but maybe enclosing the entire thing. If I am not needing to adjust the optics while it is running, i could enclose it entirely, except the variac. Maybe a pc and some sensors (temp, current, pressure maybe). Any suggestions for a cheap material? Plexiglass? I will try to find someone around here to assist if possible.
 

twelti

Member
Joined
Jan 3, 2019
Messages
40
Points
8
I think my general approach will be to start with a small pre-made tube, then build a short one from scratch, then a longer one. This way I can get the gas mixture, vacuum and high voltage parts and general safety figured out on a known working tube. The second tube will be same length as the pre-made one so I won't have to change anything in the power, vacuum systems. After all that, if I am still obsessed as I am right now :)-) I will build a folded version for higher output. I really want that since I don't have a lot of room for a long device and want to keep the voltage down but get more power out. I will design everything so that if possible I can reuse each component when I go to the next laser, and learn as I go. For example, the enclosure will be sized for the largest laser I am contemplating. Same for power supply, vacuum system etc.

I will try to find someone with high voltage savy to look over the entire setup before I power it up.

BTW, I found a very nice web page giving a lot of info on setting up and safely operating a CO2 laser: http://experimentationlab.berkeley.edu/sites/default/files/writeups/CO2.pdf
 

Anthony P

Well-known member
Joined
Oct 7, 2018
Messages
529
Points
63
There is a lot of good info in your link. The only problem is sifting out what you need and what you could get away without. There are a couple of books by Robert Iannini that detail CO2 laser construction: "Build your Own Working Fiberoptic, Infrared, and Laser Space-Age Projects" and "Build Your Own Laser, Phaser, Ion Ray Gun & Other Space -Age Projects". The second details a simple and inexpensive cooling tank.
I would stay away from the metal bellows design as they are expensive and easily lose alignment. For a folded resonator you will likely need 2 NST. Each on Heavy duty Variac( Marlin P Jones & Associates #15163 TR). Single tube only needs 1. These run on 110, you need a heavy duty house receptacle on 30Amp breaker. You will need vacuum pump, gas bottle with regulator.
I am going to send you a PM.


prop_65_tall.gif
 

twelti

Member
Joined
Jan 3, 2019
Messages
40
Points
8
I wonder if a single multi-tap transformer would work?
For vacuum pumps, do you think the el-cheapo HVAC ones you can get on Ebay for $120 would work? It is hard to find specs on what they will pull.
Is Robert Ianinni the same one who did the CO2 laser plans form Information Unlimited? I have bought those already.
 

Anthony P

Well-known member
Joined
Oct 7, 2018
Messages
529
Points
63
I wonder if a single multi-tap transformer would work?
For vacuum pumps, do you think the el-cheapo HVAC ones you can get on Ebay for $120 would work? It is hard to find specs on what they will pull.
Is Robert Ianinni the same one who did the CO2 laser plans form Information Unlimited? I have bought those already.
Vacuum pumps are sensitive creatures. They have to be well maintained and used properly. NEVER buy used. Look at JB Industries or Robinair. A pump that has been used for HVAC has been exposed to moisture, heat and refrigerants. This creates sludge in the pumps. Invest a few bucks in a decent one. Look at CFM and ultimate vacuum. Higher CFM will allow you pull a higher vacuum on leaky system. No pump will pull its rated ultimate vacuum... even blanked off and fresh out of the factory box. An isolation valve is not 100% necessary, but very nice to have. Another useful feature is a gas ballast valve. If you plan to continue to do vacuum/laser work, get a good pump and take good care of it.
Send link to the Ebay pumps and I will take a look.
 

Anthony P

Well-known member
Joined
Oct 7, 2018
Messages
529
Points
63
Cheapest good pumps I found on e-bay are Robinair 15500 or JB Industries DV-4E. Either is suitable for CO2 project. They have fancier versions with more bells and whistles, but these will work. Both are 2 stage. Those really cheap ones are single stage with lower ultimate vacuum. The CO2 laser will operate around 29" Hg. The limitations of the recommended pumps would be if you wanted to do future projects requiring a deeper vacuum. In which case a third stage would be necessary. These pumps could still be used as forepumps for Hg or oil difussion pumps if you ever went down that road.
 




Top