Nitrogen Laser Build - June 27

Science
21

The problem is that if you are using the circuit Richard provided above, the copper plane connected to the spark gap is acting like an antenna. Any form of optical shield protects against the UV; however, you really need to shield against RF from that spark, which requires conductive metal shielding. Of course, this depends upon how your power supply is functioning. I know that if your using the neon transformer I donated, then you have a different supply from what is shown above.

Also from a safety perspective, you ought to be shielding the entire top/bottom as well, since according to that circuit diagram, it is conducting +20kv on that copper path to the laser tube (apparently as a capacitor). As someone who has received a similar voltage jolt from a similar power supply for my spark gap flash tube (photography), I can assure you it is quite painful and can be lethal.

As to the ARC welders, I can’t speak to their design, but I suspect they include elements to prevent the emission of any RF or the FCC would shut down their manufacture.

22

These type of lasers have been operated all over the nation for the last forty years. I’m sure that if the spark gap were attached to a suitable antenna, the FCC would complain. However, it won’t broadcast much without the antenna.

The two problems that people talk about with this system are UV radiation and noise.

I should have mentioned to ignore the electronics schematic in the diagram; we aren’t using that part. We are using your (Walter’s) neon sign transformer.

I recall someone once told me that the copper plates aren’t effective antennas, as they are oriented horizontally.

23

@OpCode,

Just because this ‘type’ of laser is operated all over the place, doesn’t mean that it is done so without the proper electrical and RF shielding. As a HAM enthusiast, I can assure you DFW is full of HAM operators who like to hunt down and report radio interference.

Also, the shielding I am talking about would have the ADDITIONAL benefit of actually making that device shown safe to operate, by protenting any passers by from accidentally touching (or being touched by a spark from) copper that is at +20,000V of potential.

As to antenna polarization, most HF antennas used to communicate around the world are horizontally polarized. But even those that are not (vertical whips for instance), are still able to transmit and receive signals around the world. Polarization makes a difference, but not that much.

Look, I don’t want to argue about this. You asked about shielding, and I have provided my suggestions. In my opinion, the device you outlined needs RF shielding, and it needs a physical barrier to prevent hurting anyone. In my experience, plastic doesn’t make a good physical barrier at these voltages since it can have very large potentials induced on it, by such high voltages. There is a reason HV supplies typically have grounded metallic cases.

24

Thanks for your input. I appreciate your thoughts on the matter.

I don’t know what the specific RF frequency radiation would be from this device, but in thirty years of looking at actual devices, some in operation, and now readily found all over the Web, I’ve never seen anyone consider RF shielding on them. Maybe it would be a problem at DMS; that’s something to consider. Perhaps we should have someone who could measure what the affects would be when we turn it on? I’m always curious.

Several people do put acrylic shields over the top of the capacitors. I’m planning to bring a glass tabletop to support the bottom, and tell people to stand back when the device is in operation, just like they would any other dangerous piece of equipment.

25

BTW, one version of the RF interference from these type of devices is labeled as an Electromagnetic Pulse… Which should give you an idea of the range of interference one can expect from devices like this. Now I am not saying your EMP generator has enough power to ‘destroy’ anything (except possibly that Scientific Computer a few feet away), but it does have the potential to generate a lot of interference for other members.

26

Think of the acrylic on top of the capacitor like another ‘layer’ in the capacitor. Air at these voltages is conductive, so the acrylic can accumulate VERY large electrical charge, several orders of magnitude greater then the voltage actually on the capacitor. Think large static electric charge. By itself that is only a minor annoyance; however, when you have a static discharge (think it jumping to someone a foot or more away), you provide a conductive path for the main +20kv to ground through the target of that initial static discharge.

I strongly suggest a grounded metal case to isolate any of the high voltage parts of your laser. I doubt you could show me a commercial laser (or other high voltage device) that doesn’t have such shielding. And I strongly suggest that you don’t take the momentary survival or lack of injury of youtubers as proof that what they are doing is safe.

Anyway, best of luck!

27

FWIW, I’m planning on using 9kV from the neon sign transformer that you donated. That might be sufficiently-high voltage. If not, I could run it through the voltage multiplier that I built and operated for my class on laser power supplies decades ago (if I can remember how to operate it).

28

You need DC right (assuming so since you said you can use a voltage multiplier)? If so, I suggest winding a DIY inductor to use with whatever output capacitor your using on your power supply filter to provide significantly better filter rejection. Such a DIY inductor is cheap and easy to make, and it is amazing how much less ripple you will see on the DC output.

29

I don’t have to use DC; the laser works fine on AC (the direction of discharge changes on each cycle).

30

The first place I look for those kinds of things is McMaster Carr

1 Like
31

The following website has useful information on building a nitrogen laser:

http://jonsinger.org/jossresearch/lasers/nitrogen/dkdiy.html

32

Did you see this quote on that site?

The reason I know that the EMP from one of these can damage equipment is that I have done so.

33

Yes, I saw that. I noticed, also, that it referred to equipment attached to the laser, not just equipment nearby.

34

That is only because a direct wired connection, like anyone else on the same electrical circuit, makes for an easier path. But it isn’t the only path for such damage.

35

Walter,

I can appreciate your broad knowledge in many areas including that of a HAM radio operator, but I have worked as an electromagnetic consultant specializing in RF interference for over 13 years plus I have a recent degree in Electrical Engineering.

As to the ARC welders, I can’t speak to their design, but I suspect they include elements to prevent the emission of any RF or the FCC would shut down their manufacture.

Sure, they sprinkle magic RF attenuation dust on the outer casing and voilà! Static be gone…

Not true. Try listening to an AM radio while someone is using a stick welder 20 feet away and tell me what you can hear above the sound of spattering metal.

They may have components that cut down on CONDUCTED RFI in the power line, but there is nothing that prevents the broadband RADIATED noise from the arc itself. I have consulted on numerous jobs where very high powered RF clamshell welders caused substantial computer interference (not damage) at VERY CLOSE range only. RF power falls off very quickly with distance.

I am not saying that this setup will not put out any noise, in fact I am certain it will. But to a degree that requires a Faraday cage? I seriously doubt it, but we are all curious DMS members so how about we measure it?

I have a number of RF meters and a Line Noise EMI Meter. Let’s give it a try and see what we come up with before enclosing the laser inside of a reactor vessel.

Sound good?

At the worst, we will learn something!

I even have a computer we can test it on… I want to see if it goes BOOM!

JAG “White Noize from the Southern Boyz” MAN

1 Like
36

AS you know a faraday cage is simply metal shielding. Not tough nor expensive to implement. And it will make the operation of the laser significantly safer.

And you may not be aware, but about 40 feet above your broadband spark generator the DMS amateur radio committee has several antennas, which I guarantee you will interfere with if someone is using that radio when you power up the laser.

As I said above, I am simply making a suggestion. But if youll radiate a lot of noise there are a large number of local hams that can triangulate the source and love filing complaints with the fcc.

$10 in sheet metal and about a man hour would all but eliminate the potential problem.

37

Walter,

AS you know a faraday cage is simply metal shielding. Not tough nor expensive to implement. And it will make the operation of the laser significantly safer.

Yes, a faraday cage much like the structural metal of the DMS building itself (particularly the warehouse) if I am not mistaken so there is most likely already some shielding already present between the interior and exterior.

And you may not be aware, but about 40 feet above your broadband spark generator the DMS amateur radio committee has several antennas,

I am well aware of the Amateur Radio Committee and that there are several antennas nearby - I would also like to know what the characterization of the background noise level is with all of the machinery running, compressor kicking in, the welders being used, etc.

which I guarantee you will interfere with if someone is using that radio when you power up the laser.

And I would love for someone from the committee (you if you will accommodate) to turn on one or more of the radios while the laser engages because I want to hear the effect for my own experience.

As I said above, I am simply making a suggestion. But if you’ll radiate a lot of noise there are a large number of local hams that can triangulate the source and love filing complaints with the fcc.

And I am one of the people who gets hired to find these sources by individuals, corporations and other large companies.

I have already considered the potential effect of the laser on HAM radio and it makes sense to first be more concerned about the immediate, localized influence of the spark gap on the DMS group’s equipment. Also, it is not like this is going to be on 24/7 - Richard, how long are these test firings typically?

What I want is some empirical data with a known source and here is a great opportunity. I agree with the recent statements that both you and Richard made.

You don’t want to argue, and Richard would like to take some readings.

$10 in sheet metal and about a man hour would all but eliminate the potential problem.

Okay - make you a deal.

You have superior metal fabrication skills and I would like to learn. (I signed up for your Bridgeport Mill class for instance) Indulge my curiosity in exchange for showing me how to build the cage out of sheet metal.

Plus any results can be recorded as part of the Science Committee.

Win, win, win.

JAG “Electromagnetic Cheshire Cat” MAN

1 Like
38

I ought to plan ahead for us to conduct some quick experiments, such as making radiator antifreeze glow or even lase. That should be either easy or impossible. Based on the fact that operation of the laser likely would produce enough noise for it to be irritating to the people nearby, I’d say we wouldn’t run it more than a few minutes at a time without good reason.

Later, when we begin doing experiments… well, we probably want to improve this laser before we begin doing other experiments. Right now, the laser is the experiment!

I read last night that some researcher in the '80s used a nitrogen laser to perform cellular surgery. Apparently, he was amputating dendrites from nerve cells using the nitrogen laser beam. More common uses are pumping dye lasers and performing spectroscopy.

2 Likes