Gain limitations in TE CO2laser amplifiers

The factors which limit the small-signal gain of TE CO2laser amplifiers are investigated with a novel technique based on gain measurements of the sequence, hot, and regular CO2laser bands. This new technique enables us, for the first time, to determine accurately and independently the rotational and vibrational temperatures characterizing the CO2laser system. The gain ratio of the sequence band (00° 2) to the regular band (00° 1) provides a simple and accurate determination of the ν3mode vibrational temperature. It is found experimentally that the ν3mode vibrational temperature saturates at a high input discharge energy. This saturation sets an upper limitation to the gain attainable in TE CO2laser 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 CO2laser dynamics and the validity of our measurement technique for vibrational temperatures.