Relaxation Oscillation in Transient Output of Pulsed CO2 Laser

Abstract

A periodic undulation was observed in the output of a 10.6 µm CO2 laser in the afterglow region of the pulsed discharge, while no undulation appeared in the output of a 9.6 µm CO2 laser under any of the experimental conditions studied. It is shown that the observed undulation is due to the relaxation oscillation and occurs in the balance between the rate of induced emission from the upper laser level and the rate of relaxation from the lower laser level. The rate equations for the model of the lasing system give the solution of the relaxation oscillation, even when the continuous pumping to the upper laser level is absent but the fast relaxation from the lower laser level is present. The calculations give a good description of the characteristics of the undulation, which depends on the partial pressures of the constituent gases. The relaxation rate constant relevant to the lower laser level (100) was determined from the analysis as ∼4.2×103/(Torr·s) (CO2–He). This agrees well with values previously obtained by the infrared pulsegain method.