Prelasing investigations of recombination of chlorine atoms

An experimental investigation was made of radiative recombination of chlorine atoms in order to study the feasibility of developing a gasdynamic recombination laser utilizing electronic phototransitions. Nonequilibrium atomic concentrations were obtained using a method of thermal dissociation of molecular chlorine in a shock tube followed by rapid cooling in a supersonic nozzle. Small-scale nozzles were used for rapid cooling. Recombination luminescence at high (>10/sup 17/ cm/sup -3/) nonequilibrium atomic concentrations was observed for the first time experimentally. The downstream distribution of the radiation intensity in the supersonic nozzles was studied. It was found that the radiation was in the near infrared in the 800--1100 nm range. A shift of the spectra toward the red and narrowing with cooling was observed. A theoretical estimate was made of the rate of vibrational relaxation of chlorine molecules under the experimental conditions. It was shown that light amplification should occur for phototransitions to high vibrational levels of the ground state. From measurements of the absolute radiation intensity in various spectral ranges, it was possible to estimate the gains feasible under experimental conditions: (5 x 10/sup -4/)--10/sup -2/ cm/sup -1/.