I have made a third much smaller nitrogen laser but with higher power and it can be fired a lot faster.
“Continue reading” for more details and photos.
In addition I have a dye to highlight the beam. This was made by dissolving some fluorescent yellow marker pen dye in water.
Note the absence of sparks in the channel, just the glow of ionization spread fairly evenly. The beam is being reflected off some shiny aluminium foil. The spark gap is made of sections of brass tube.
I have taken oxygen from a cylinder, blown across the laser channel. It completely extinguishes lasing for 4 or 5 seconds and it is not restored for almost 20 seconds. Oxygen is poison! It also increased the intensity of the sparks in the channel. Note that none of these lasers, at least so far, have used pure nitrogen.
An interesting fact. I have made all my nitrogen lasers with no new expenditure. All equipment was available as scrap. In other words, they cost nothing. A pleasant change for laser stuff.
I am curious about my laser output. Certainly the output from yellow marker fluorescence is much lower than a 1 mW diode laser. Granted the UV output may be brighter depending on the efficiency of the fluorescence. A UV LED is not that bright either but I don’t know the output of the one that I have although typical eBay ones (from 2004) are 2000 mcd.

Here is a comparison of a N laser beam of about 2mm compared with a 20mm beam of a 5000 mcd blue LED (running at its rated 20 mA). The brightness is about equal but the area of the LED is 100 times greater. Hence the brightness of the UV paper fluorescence is about 50 mcd for my laser.
I seem to recall a 14000 mcd LED has about 5 mW output, hence 50 mcd = 0.018 mw. A long way from burning paper or causing tissue damage.
I have a photodiode linked to my frequency meter tonight to count the flash rate. The photodiode wavelength response is down to only 5% at 400 nm and presumably much lower at 331 nm but still seems to function directly sufficient to trigger the meter. In practice it is easier for aiming to put some yellow marked tissue paper in front of it and the yellow fluorescence will be much closer to it optimum wavelength.
For repetition rates of 1 to 50 Hz the voltage after the resistor is surprisingly constant at around 5.5 kV and drops to about 4.5 kV as the rep rate rises to over 200. Note that my HV meter reads peak DC or peak AC so these values are averages.
The greatest total brightness for nitrogen laser 3 is between 150 – 200 Hz and definitely falls off after that. I must admit that this is faster than I had expected. My impression (which has not been tested yet) is that my older larger nitrogen laser doesn’t tolerate fast rep rates. Note that 200 Hz may not be giving the greatest power per pulse. I could get some idea by measuring relative powers with the blue diode setup as described above but will have to set that up properly.
I measured my power input today.
1 With no sparks: There is 200 uA leakage at 5 kV = 1 watt before any discharge.
2 At a rep rate of 8 input current rises to 500 uA ie 300 uA above the leakage current. This would suggest an input current per pulse of 37 uA.
Power per pulse is around 200 mW and total power input is 1.6 W
3 At a rep rate of 200 input current is 6 mA. This would suggest an input current per pulse of 30 uA with voltage dropping to 4.5 kV.
Power per pulse is around 135 mW and total power is 27 W.
In terms of efficiency, 27 W in and a lower limit of .018mW out gives a spectacular efficiency of around 1 in a million or .0001%. How cool is that.
While these figures are a bit rubbery, they serve to give an idea of powers involved. The average voltage falls at higher rep rates but the peak input voltage must be rising or else it wouldn’t spark faster!
Nevertheless the power input per pulse seems a lot smaller at higher rep rates, hence the limit may not have been reached and the fall in output may be due to power supply issues rather than inversion states with nitrogen lasing at air pressure.
At full power I am overdriving my MOT (about1.5 kW input) and the dielectric is not likely to last long either at 27 W input.
I did try my older and larger N laser but couldn’t get much above 50 Hz before arcing starts to intensify at different points which I suspect is due to localised dielectric heating prior to melting and burning. The larger currents with the bigger capacitor are probably the issue here although most of the current “misses the boat” in terms of lasing.

Related pages

  Nitrogen laser 4

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Photo Date: 2004