Surface plasma in a cw CO2 laser beam

An experimental study was made of a plasma near the surface of a metal subjected to cw CO₂ laser radiation of ~10⁶ W/cm² power density. It was established that evaporation of a metal in air could create a steady-state erosion jet without optical breakdown of the vapor. When the threshold conditions were exceeded, a surface optical discharge was struck in the metal vapor, but up to 2×10⁶ W/cm² the air surrounding the target was not ionized and the optical discharge did not propagate in the air from the target toward the laser. The results could be of considerable practical importance in the selection of the conditions for the processing of metals by CO₂ laser radiation.