Experimental investigation of the optical properties of laser erosion plasma in the interaction zone

An optical study was made of the surface plasma generated in an open interaction zone by laser radiation of 6 · 10⁶ W/cm² density impinging on a metal. A characteristic emission of a continuous background and of spectral lines by the surface plasma was reported. It was established that the continuous background reached its maximum intensity at some height from the surface being irradiated. The transparency of the plasma was determined using an optical system in which the distribution of the transparency could be determined in a single experiment. It was found that plasma jets generated by laser erosion were optically opaque in a surface region up to 2 mm thick. The measurements were used to determine the temperature distribution along the plasma jets in the surface region (0.3–2 mm). The temperature had a maximum due to heating of the plasma jets by the laser radiation in the course of their gas-dynamic motion. This maximum indicated strong screening of the surface from the incident laser radiation.