High vibrational temperatures in optically-pumped CO/sub 2/

A pulsed 4.3- mu m CO/sub 2/ laser was used to optically pump mixtures of CO/sub 2/ and He, and create transient gain at 9 and 10 mu m. A conventional continuous-wave CO/sub 2/ laser operating on both regular and sequence bands measures this transient gain, and determined the nu /sub 3/ (asymmetric stretching)-mode vibrational temperature T/sub 3/. The measured values of T/sub 3/ are generally much higher than those attained in discharge-excited CO/sub 2/. It is shown that a Treanor distribution must be used to describe the populations in the nu /sub 3/-mode when dilute mixtures of CO/sub 2/ in He are optically pumped to nu /sub 3/-mode temperatures of 3000 to 4000 K. Under these conditions the sequence-band gain coefficients are almost equal to those on the regular bands. The collisional relaxation of energy from the nu /sub 3/ mode shows evidence of fast V-T relaxation at high values of T/sub 3/, followed by a slower relaxation rate characteristic of the 00/sup 0/1 population lifetime.<
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