Breakdown of a gas on a metal surface by a CO2 laser pulse of duration 10–1000 μsec

A study was made of plasma formation on a metal surface under the action of a rectangular pulse of CO₂ laser radiation. It was found that for each metal there exists some critical radiation intensity below which optical breakdown occurs in the target material vapor formed after heating the surface to the boiling point. In this case, the experimentally measured time for breakdown to develop is in good agreement with theory. However, if the radiation intensity exceeds the critical value, the breakdown undergoes a discontinuous shift to the leading edge of the laser pulse and does not involve heating of the surface to the boiling point.