GAS BREAKDOWN BY A CO2 LASER BEAM NEAR A METAL SURFACE WITHOUT RAPID EVAPORATION.

Laser breakdown of air and other gases can occur near the surface of a refractory metal in the absence of rapid evaporation. The concentration of metal vapor above a laser-bombarded surface is calculated. It is demonstrated that the initial degree of ionization of the air and the absorption coefficient for the laser beam are determined primarily by the metal vapor in the air. A breakdown condition is derived; this condition gives the minimum surface temperature at which the gas near the surface may undergo breakdown. The breakdown delay time is calculated.