Gain limitations in TE CO2laser amplifiers

The factors which limit the small-signal gain of TE CO
2
laser amplifiers are investigated with a novel technique based on gain measurements of the sequence, hot, and regular CO
2
laser bands. This new technique enables us, for the first time, to determine accurately and independently the rotational and vibrational temperatures characterizing the CO
2
laser system. The gain ratio of the sequence band (00° 2) to the regular band (00° 1) provides a simple and accurate determination of the ν
3
mode vibrational temperature. It is found experimentally that the ν
3
mode vibrational temperature saturates at a high input discharge energy. This saturation sets an upper limitation to the gain attainable in TE CO
2
laser amplifiers. As we can measure all the characteristic temperatures relevant to the gain medium, a detailed comparison between the calculated and experimental gain can be carried out with no variable parameters. The result of such a direct comparison confirms both the validity of the conventional "mode temperature" model for CO
2
laser dynamics and the validity of our measurement technique for vibrational temperatures.