TEA Nitrogen laser problems (homemade)

[Pieznice29]

I'm pretty sure this is the right section to be posting this...
I've been meaning to build a TEA nitrogen laser for a while now, only just got round to it.

My setup:
I have a 2mm thick piece of glass thats roughly 35cm by 25cm from an old scanner seperating 2 pieces of alaminium foil aprox 30cm by 20cm on either side. The glass is placed hoizontaly with the lower piece of foil being used as the ground. The upper sheet of alaminium foil is split into 2 about 2/3rds of the way along its length. I originally split it 50/50 but after seeing other designs I decided on the current configuration. I used the smaller top side for the HV in with sparkgap to ground, this is linked to the other side with 3 4.7Mohm resistors in series (using 1 or 2 just resulted in them arcing over). There is a 5mm gap between the 2 upper sheets of foil, between this gap are the laser electrodes. I tried many different electrodes but so far haven't had any luck. I'm currently using blanking plates from a computer case. Entire lasing channel is roughly 10cm long.

Power supply:
I'm using my homemade CO2 laser power supply with a handful of 4M7 resistors in series to limit the current. The power supply consists basically of a ZVS (push-pull) driver and a half-wave recitifed TV flyback transformer. It outputs aproximatly 20kV when used like this.

My problem:
I can't for the life of me get the laser to give any output, all I see is one or 2 sparks between the laser electrodes at fairly consistant places each time the sparkgap fires. I have tried moving and altering the electrodes many times, so far the most I have achived is about 10 to 15 sparks between the electrodes firing consistantly. From what I understand I should be getting a very even plasma discharge between the electrodes down their entire length.

Does anybody have any ideas on how I can achive an even plasma discharge?
From what I understand about these lasers these concentrated sparks are a result of the gas pressure being too high but I don't understand how atmopsheric pressure can be too high for an atmospheric pressure laser...

Oh and heres a video < Click the text

 

[BShanahan14rulz]

have you tried moving them closer together? also, those blanks aren't always the straightest pieces of metal...

 

[Pieznice29]

Yes, i've tried gaps from .5mm to 5mm, no luck

 

[BShanahan14rulz]

After looking at a few of my blanks, they look pretty straight. I only used steel L-channels. Is there enough pressure on them to make an even connection to the foil the full length of the rails?

Power supply is where my understanding starts dropping off. From what I understand, it sounds sufficient, and it's charging the caps...

I don't know why I'm the only one responding, I've only built one of these once, and that was a long time ago when I was just looking for something to do. TEA N2 was what got me hooked on turning electricity into light. Hopefully someone will chime in with some insightful advice.

 

[Pieznice29]

I don't seem to be able to get my hands on any alaminium/steel L channels around here unfotunatly, so i'm just making do with what I have around that seems fairly straight.
Making sure there is a good connection is a good idea, so far i've just rested the electrodes on the foil and hoped for the best. I'll give it a shot when I get chance. Thanks

 

[Event_Horizon]

There are a couple of design considerations when building a TEA nitrogen laser that you may or may not have taken into account. Because you're operating at atmospheric pressure, the entire lasing process, from the start of the dischage to the last photon being emitted, takes less than 5 nanoseconds. So you need to make sure your design is nearly perfect. First of all, the spark gap itself needs to have line of sight with the entire discharge gap. The purpose of this is so that the high-energy UV photons from the spark can pre-ionize some of the gas particles in the discharge cavity making it easier for an even discharge to take place. Secondly, the spark gap should be on the smaller capacitor, and should be at the back corner of the laser, so the discharge begins at the back of the laser and flows forward. Electrode spacing and straightness are also critical. You might need to place them as close as 0.2mm apart (depending on your voltage, and I don't have my old notebook handy at the moment), and they need to have exactly the same separation distance along their entire length (a variation of even 0.01mm can potentially ruin the whole thing. You may want to consider lightly sanding the electrodes down until you are sure they are completely straight.

Also, your insulation material (glass) may be too thick for the capacitor to store enough energy. I would recommend that plastic insulation vapour-barrier stuff they use in home construction to keep moisture out of the insulation, two layers of it is less than 0.2mm thick and I've seen it successfully used for these lasers before.

I hope this information helps. You should check out this page if you haven't already:
The Professor's Homebuilt Lasers Site - Nitrogen Laser
The guy was my professor in college and he knows what he is talking about.

Also I'm sure I don't need to tell you about the dangers of the high-voltage, but do also keep in mind that both the spark gap and the cavity dischage (nevermind the laser output itself) produce non-trivial amounts of UV light so be careful not to look directly into it whenever possible.

 

[Pieznice29]

There are a couple of design considerations when building a TEA nitrogen laser that you may or may not have taken into account. Because you're operating at atmospheric pressure, the entire lasing process, from the start of the dischage to the last photon being emitted, takes less than 5 nanoseconds. So you need to make sure your design is nearly perfect. First of all, the spark gap itself needs to have line of sight with the entire discharge gap. The purpose of this is so that the high-energy UV photons from the spark can pre-ionize some of the gas particles in the discharge cavity making it easier for an even discharge to take place. Secondly, the spark gap should be on the smaller capacitor, and should be at the back corner of the laser, so the discharge begins at the back of the laser and flows forward. Electrode spacing and straightness are also critical. You might need to place them as close as 0.2mm apart (depending on your voltage, and I don't have my old notebook handy at the moment), and they need to have exactly the same separation distance along their entire length (a variation of even 0.01mm can potentially ruin the whole thing. You may want to consider lightly sanding the electrodes down until you are sure they are completely straight.

Also, your insulation material (glass) may be too thick for the capacitor to store enough energy. I would recommend that plastic insulation vapour-barrier stuff they use in home construction to keep moisture out of the insulation, two layers of it is less than 0.2mm thick and I've seen it successfully used for these lasers before.

Don't worry, I've done my homework (Or at least some of it...)
From what I understand, due to the lasing process happening so fast and being so short, I need to dump as much energy as possible into the nitrogen as I can from my capacitor in that time. Any stray inductance and resistance needs to be done away with. Because i've never done anything like this before I find it hard to guage how much adding say another wire will inhibit the laser from lasing, so I was kind of just playing around with various configurations until my piece of paper at the end of the laser flouresces.

I've never heard of the spark gap being used to ionize the laser electrode gap before, which is why I hadn't done it. It's a great use of that spark gap though, I shall move my spark gap when I get chance.

For the insulation; I tried a few other insulating materials before I used glass. For example, at first I used those thin plastic wallets used to hold sheets of paper in binders but they just broke down and began to arc and burn between the layers of foil. I'll go have a look around, see what I can find thats thin and can stand ~20kV

I hope this information helps. You should check out this page if you haven't already:
The Professor's Homebuilt Lasers Site - Nitrogen Laser
The guy was my professor in college and he knows what he is talking about.

Thats where I learnt most of what I know about nitrogen lasers, and many other lasers too. Very nice website, bookmarked it long ago...

Also I'm sure I don't need to tell you about the dangers of the high-voltage, but do also keep in mind that both the spark gap and the cavity dischage (nevermind the laser output itself) produce non-trivial amounts of UV light so be careful not to look directly into it whenever possible.

I use laser goggles rated for 405 and 445nm lasers whenever im using this, I assume they are good for blocking the deeper UV wavelengths too. Or at least I hope so...

Thanks for all the info

 

[Seoul_lasers]

I'm pretty sure this is the right section to be posting this...
I've been meaning to build a TEA nitrogen laser for a while now, only just got round to it.

My setup:
I have a 2mm thick piece of glass thats roughly 35cm by 25cm from an old scanner seperating 2 pieces of alaminium foil aprox 30cm by 20cm on either side. The glass is placed hoizontaly with the lower piece of foil being used as the ground. The upper sheet of alaminium foil is split into 2 about 2/3rds of the way along its length. I originally split it 50/50 but after seeing other designs I decided on the current configuration. I used the smaller top side for the HV in with sparkgap to ground, this is linked to the other side with 3 4.7Mohm resistors in series (using 1 or 2 just resulted in them arcing over). There is a 5mm gap between the 2 upper sheets of foil, between this gap are the laser electrodes. I tried many different electrodes but so far haven't had any luck. I'm currently using blanking plates from a computer case. Entire lasing channel is roughly 10cm long.

Power supply:
I'm using my homemade CO2 laser power supply with a handful of 4M7 resistors in series to limit the current. The power supply consists basically of a ZVS (push-pull) driver and a half-wave recitifed TV flyback transformer. It outputs aproximatly 20kV when used like this.

My problem:
I can't for the life of me get the laser to give any output, all I see is one or 2 sparks between the laser electrodes at fairly consistant places each time the sparkgap fires. I have tried moving and altering the electrodes many times, so far the most I have achived is about 10 to 15 sparks between the electrodes firing consistantly. From what I understand I should be getting a very even plasma discharge between the electrodes down their entire length.

Does anybody have any ideas on how I can achive an even plasma discharge?
From what I understand about these lasers these concentrated sparks are a result of the gas pressure being too high but I don't understand how atmopsheric pressure can be too high for an atmospheric pressure laser...

Oh and heres a video < Click the text

Try polishing your electrodes with some fine grit sand paper and re-position the hot to the centre of the electrode. You may be getting too much resistance along the discharge surface. Electricity goes to the point of least resistance... hence why I suggest polishing the discharge surface and repositioning the electrode.

Also I suggest using Tungsten Zirconium welding rod next time. Best spark gap to be found anywhere!


Additionally I'd also be using PE/ PP capacitors as they are good for HV HFreq pulse discharge applications.
DO NOT USE GLASS. Glass is lossy at High Frequency and that loss translates to heating of the dielectric.
I have some plans on making a homemade dry pulse caps and a sample of a homemade one. If you are interested I can send you a PM.
Get rid of the resistors as your plates already have enough (too much) resistance!

 

[Seoul_lasers]

Here is a picture of a capacitor I built using PE film. Actually this is 1mil PE sheeting. 3x3 layers of sheeting. Total charged plates = 3. Each sheet is about 1mx1m square. 86cmx86cm is the charged surface.
This thickness is good up to 40Kvdc or 14.4Kvac. It is hand wound and uses Aluminum foil as the charge plates. Total capacitance is about ~20nF @ 40Kvdc. Fully charged it can easily deliver a few 100A's !

This would make your TEA nitrogen sing!

 

[blrock]

I built a TEA nitrogen laser around 2001. I used an HT from a small TV. I tried and tried and tried and tried and eventually got it to lase. I then terminated the project. They are so noisy to operate it was actually anoying me. For quick results, use a closed cavity with some low pressure N2.

Still a nice feeling when it does lase and you can tell yourself that you produced coherent light!

Good luck

 

[Bluefan]

Seoul_lasers, you necroposted (that's brining up a very old thread probably not relevant to the OP anymore) and doubleposted. Try not to do that.

I had a try on an N2 laser too, but it never worked. I used clear tranparencies from an overhead projector and aluminum foil to make capacitors, tha may not have been a good choice.

 

[regalis]

I found a nice youtube video just 5 minutes before reading this thread
Look here: Homemade dye laser using Coumarin - YouTube

 

[Seoul_lasers]

Seoul_lasers, you necroposted (that's brining up a very old thread probably not relevant to the OP anymore) and doubleposted. Try not to do that.

I had a try on an N2 laser too, but it never worked. I used clear tranparencies from an overhead projector and aluminum foil to make capacitors, tha may not have been a good choice.

Hey just trying to help. I double posted to post the pic of the pulse cap. It is relavent to the thread. The post was on a recently posted list. I saw it and jumped in.

 

[Bluefan]

There is an edit function if you want to include things into an already made post. Also, I'd say ~2 month old would be a bit old, but in a not so busy forum section you're probably right it's not that old. But consider the remark just as a suggestion, nothing more.

Your cap does look very nice, have you made an N2 laser with it? I've heard of rolled up caps before, it looks like a neat way to amke it more compact. What kind of material is a PE sheet? I'm trying to find suitable materials for a cap, but I don't have much succes yet. would 1 mil thick be 0.025mm thick? That's quite thin, did you test it at 40kV?

 

[regalis]

PE=polyethylen (Plasticbag material i assume)

 

[Seoul_lasers]

PE=polyethylen (Plasticbag material i assume)

This is a sheeting for making forms from. It is very stiff. I originally said 1mil. It is actually 2.5mil with 1mil foil. Yes, it has actually taken up to 40Kvdc and survived. measures around 20nF. More than enough energy to do some damage.

I made a N2 laser from it a while back using a Car Ignition coil and a mosfet driver. I had it
running ~35Kvdc. IT worked well but I killed the laser in about 10 minutes. I melted the rails from the discharge current. It was also FAR too loud. I'm guessing the discharge current was in the neighbourhood of ~3-400As 120Hz.
I also tried making a mini N2 (air) laser from a stun gun kit. IT actually worked quite well.


I think the next time I try a N2 laser, I will get a professional tube made at a neon shop out of quartz glass (IF) it is possible.