Optimization of gain zone reduced fields in rf-excited CO₂ lasers.

The authors report the results of a systematic study of laser power optimization with respect to the main parameters available for selection in a plane parallel-geometry RF-excited laser. Experiments have been conducted for discharge electrode separations in the 4-10-mm range with the generator frequency and gas pressure as parameters. Measurements have been made of laser power output, interelectrode voltage, RF current, and gas tempertures for a square cross-section geometry of 200-mm length. A time-dependent model of the a-type RF capacitive discharge has been developed that allows for the voltage drop that occurs in the sheath region of the discharge close to the electrodes. Using this model, it is possible to determine internal discharge parameters such as the gain zone reduced field E/N and the mean electron energy and electron density. It is found that for all values of discharge cross section, the highest laser power is obtained for the frequency and pressure at which the calculated value of E/N, taking into account the gas temperature, is closest to the theoretical optimum value for pumping of the laser levels.