Ahhh, this discussion really takes me back to when at 14 I built this very style of Nitrogen Laser. Unfortunately, it’s so long ago that I don’t have any hints or recommendations.
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I strongly encourage that you maintain physical contact between the grounded discharge probe and the capacitor for at least a full minute, and longer if measurements indicate otherwise.
The estimates that the formulas you used are basically fine; however, there are a number of assumptions embedded in them. Most notably that the resistance will remain constant over the discharge period. The problem is that with real world components, particularly when you putting hundreds of watts of power through them they heat up. Resistance in components change with temperature.
It is better to be safe, and keep contact for at least a full minute.
BTW, the resistance through your body was likely MUCH higher then 50K, because the resistance between your body and earth ground is in series. And if you were wearing shoes, it should have been quite a bit higher. The latter is why standing in water and getting shocked is so much worse. You only have your bodies resistance to deal with at that point.
Most of the trouble we are having at this point stems from my decision to pull a Tim Allen for “More Power,” by making the laser cavity about a yard long. Jim Small had suggested in his “Scientific American” article that it should be possible to scale the nitrogen laser up to a meter long, resulting in megawatt beams, but the plans were for devices half that size or less. The problem with increasing the size is that the material used (plastics) aren’t dimensionally consistent at large sizes, and everything is more difficult to handle. Also, it’s difficult finding double-sided circuit board more than two feet long.
Agreed. Capacitors have the bad habit of “charging back up”, which is caused by:
Lesson: leave a resistor (100k, 1M, whatever) across those caps in storage or when you think you’ve discharged them already.
Unless I am gravely mistaken about the way lasers work (and I could be), you would need a 15,000V power supply capable of delivering in excess of 60 AMPS of current to provide a megawatt of power…
Which raises the question in the context of the author’s claim. Does increasing the size of the lazing chamber require an increase in power provided to the circuit? Simple common sense would seem to indicate it does, but I have no experience with lasers so I will leave that as a question for others.
On a side note, my basic practice when working from someone else plans for something I haven’t built before is to replicate them as closely as possible first, then (and only then) start tweaking the design.
It’s a pulsed laser, so we would only need pulses of high current, and, considering that the laser is less than 1% wall-plug efficient, we would need much more than 60 amps. The key to making a nitrogen laser (or other three-level laser) work is exciting the lasing medium to its upper laser level quickly; otherwise, population inversion wouldn’t be possible. For the nitrogen laser, the excitation needs to happen in less than about 20 ns (maybe much less, depending on the specific conditions). That’s why we can get away with using a pF capacitor as the current source. If we wished, we could use a 9V battery, instead of a neon power supply plugged into the wall outlet, but the charging time would be much longer (dropping the cycling rate from 120 Hz to 6 Hz).
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