TEA Laser Question

quote: My question; why not eliminate the left plate and just short the left lasing electrode to the bottom plate through the spark gap? Thanks, Mike

beginners explanations simplifing a lot of the physics:

look up "traveling wave laser" or "Blumlein circuit", although that is not a true "Blumlein"

A hypothetical quickie for beginners explanation (but very wrong) is by collapsing the voltage on the smaller capacitor (left plate)very fast, you can a even shorter discharge surging back across the main gap.

If the spark gap is at one corner of the laser, and the capacitor electrode is properly shaped, you can get the discharge energy to "walk" down the electrodes nearly in phase with the lasing action, but that is not the case here.

google "Sam's Laser FAQ," and look up nitrogen lasers. Steve Roberts

A little bit better explanation, as the left plate discharges its voltage swings below zero, as the main gap starts to conduct, so you now have a faster discharge with a much greater voltage across the gap, The nitrogen's laser upper state is just a few nanoseconds long, you need maximal energy transfer in the shortest possible arc time to excite it. The long plates drasticly lower the inductance of the circuit.

Steve Roberts

Thanks for the info, it sounds like you get ringing and the second swing is negative with respect to the bottom plate so the lasing gap potential is increased. I don't see how the second (left plate) helps cause that action to happen. Mike

The spark gap acts like a small inductor (tens of nH) in series with a small resistor (maybe 50 ohms?). The left cap and this inductance form a series LC circuit that in the absence of the main laser gap and right cap will ring down as an exponentially damped sine wave with peak positive value with respect to ground equal to the inital charge voltage, and peak negative value slightly less (due to loss in the "resistor") than minus the initial charge value, so the sine wave is basically centered on zero. The inductance connecting the left and right caps for charging is much larger than this so on this ringing timescale the tops of the left and right caps are only connected by the main laser discharge gap. The maximum voltage across the laser gap is slightly less than twice the charging voltage, but usually the gap voltage will never reach this value. Instead, once the gap voltage exceeeds the breakdown voltage (determined by the gas composition and pressure, electrode spacing and shape, and any predischarge ionization) the gap voltage will fall to some low value (hundreds of volts, maybe) and the discharge gap current will quickly rise as both caps discharge across the gap. This current risetime must be faster than the lifetime of the upper lasing level to get efficient excitation and a population inversion, and the ristime is controlled by the gap inductance, the capacitance, and the self inductance of the capacitor leads (which is partly why those leads are big sheets of material). You could actually leave out the right capacitor but if the caps are equal in size you would lose half the peak voltage, excitation energy and laser output.

-- Regards, Carl Ijames carl dott ijames aat verizon dott net (remove nospm or make the obvious changes before replying)

"amdx" wrote in message news:ba80b$47922cf3$450139ad$ snipped-for-privacy@KNOLOGY.NET...