Gain Characteristics in Optically-Pumped CO2

Abstract

Optical pumping at 4.3 µm is used to create high gain coefficients and high vibrational temperatures in the asymmetric (V3) mode of CO2. A pulsed 4.3 pm CO2 laser excites mixtures of CO2 and He to create transient gain at 9 and 10 µm. A conventional cw CO2 laser operating on both regular and sequence bands measures this transient gain and thus determines the v3 mode vibrational temperature T3. The measured values of T3 are generally much higher than those attained in discharge-excited CO2. It is shown that a Treanor distribution must be used to describe the populations in the v3 mode when dilute mixtures of CO2 in He are optically pumped to v3 mode temperatures of 3000 to 4000 K. Under these conditions, the measured sequence band gain coefficients are almost equal to those on the regular bands. The collisional relaxation of energy from the v3 mode shows evidence of fast V-T relaxation at high values of T3, followed by a slower relaxation rate characteristic of the 00°l population lifetime. Attempts to create lasing by utilizing the partial inversion predicted in high-lying v3 band levels were unsuccessful.