<p> The characteristics of small-signal gain in a TE CO₂ laser amplifier are investigated using a new technique based on gain measurements of the sequence, hot and regular CO₂ laser bands. This new technique enables us, for the first time, to determine accurately the rotational and vibrational temperatures characterizing the CO₂ laser system. The gain ratio of the sequence band to the regular band provides a simple and accurate determination of the ν₃ mode vibrational temperature. The variation of this ν₃ mode vibrational temperature with discharge energy enables us to determine the net pumping efficiency to the ν₃ mode levels as a function of input energy. It is found that the ν₃ mode vibrational temperature saturates at high input energy. This saturation sets an upper limit to the gain attainable in TE CO₂ laser amplifiers. Once this saturation occurs, increasing background gas temperature causes a reduction in gain at high input energy. </p> <p> As we can measure all the characteristic temperatures relevant to the gain medium, a comparison between the calculated and experimental gain can be carried out with no adjustable parameters. The result of such a direct comparison confirms both the validity of the conventional "mode temperature" model for CO₂ laser dynamics and the validity of our measurement technique for vibrational temperatures. </p> <p> The results of the present study have shown the existence of a de-excitation mechanism occurring in the discharge, which reduces drastically the pumping efficiency to the ν₃ mode at high discharge energy. It is therefore essential to incorporate such a de-excitation mechanism in the accurate modeling of CO₂ laser dynamics. The present study contributes to a better understanding of CO₂ laser dynamics at high discharge energies. </p> / Thesis / Master of Science (MSc)