Effects of foreign gases on the pulsed operation of a CO2 laser

The time behavior of the pulsed output from a 10.6-μm CO2 (2.2 Torr) laser with a foreign gas additive, such as CO2, He, N2, or Xe, was studied. Its operation was accomplished by a pulsed discharge method with a current pulse width of about 7 msec. The peak current was varied from 30 to 700 mA. Each gas mixture was filled into a discharge tube of 2-cm inner diameter and 70-cm length. A nonflowing gas system was used. The laser output from a CO2-only discharge was saturated at the initial part of a current pulse and quenched, so that the laser output could not continue to radiate out during the current pulse. The laser pulse width, much shorter than the current pulse width, was almost independent of CO2 gas pressure but decreased with increasing discharge current. Addition of He to the CO2 laser system strongly quenched the saturation effect in the pulsed operation and increased either the output pulse width or the peak power. Addition of N2 increased the output pulse width, but not as much as He. In the pulsed operation of a low discharge current, the N2 gas additive increased the laser peak power much more than the He gas additive, contrary to what one expects from the results of cw operation. It was newly observed that the discharge current was suppressed at the initial part of a current pulse by adding N2 gas to a CO2 discharge and that the laser beam radiated only during its suppressed period. The Xe additive slighly affected the laser pulse and the discharge current. The laser pulse width decreased to approach a constant value of less than 0.3 msec with increasing discharge current for a given gas mixture.