WA2--Comparison of theory and experiment for a transversely excited high-pressure CO2laser

Small-signal gain and laser output power have been measured as a function of time for a pin-resistor transversely excited atmospheric (TEA) CO
2
laser gain device. Both fixed-mirror and
Q
-switched rotating-mirror laser cavities were studied. A set of coupled differential equations describing the mechanisms underlying gain and lasing behavior are presented. Electrical excitation of the CO
2
and N
2
vibrational modes, collisional relaxation of vibrational energy, and interaction with TEM
00
and plane-wave laser radiation are explicitly treated. Electrical excitation is calculated using the measured time-resolved voltage and current input to the TEA CO
2
gain tube in conjunction with a simple model of the discharge geometry. A single adjustable parameter relating to the physical extent of the electrical discharge enters the calculations. Direct comparisons are made between the measured quantities and the numerical predictions of the model. The value of the adjustable parameter that gives close waveform fits is consistent with the results of other experiments. Use of the rotating-mirror
Q
-switched cavity resulted in laser pulses with enhanced peak power for one set of the device parameters studied. An explanation of the phenomenon is presented and a limitation on the applicability of the technique in terms of gas mixtures is discussed.