Instability of continuous optical discharge

A continuous wave CO2, laser beam was focused in a gas thus maintaining plasma initiated by other means. It was noted that convective flow parameters oscillate with steady frequency. This frequency depends on the pressure and sort of gas but not on the power of the laser beam. Theoretical considerations show that the oscillations are due to gas-dynamic-type instability. The criterion for instability was checked in experiment. Those oscillations influence plasma. This influence is stronger for higher pressure. This effect may explain the hitherto unexplained extinction of the discharge when the pressure reaches a certain (upper) level. (author)