Laser-plasma interaction during visible-laser ablation of methods

Abstract

We have investigated the dynamics of high-radiance visible-laser interacts with a metal vapor plasma during laser ablation of aluminum and carbon steel. The experiment with a copper vapor laser reveals strong plasma-absorption induced ignition at laser intensities above 1-2 GW/cm2. Approximation based on hydrodynamic relations indicates that the vapor density at the end of the 40-ns laser pulse is 3 X 1020-1 X 1021 cm-3 with a pressure of a few thousand atmosphere at the target surface. This high-density vapor with a temperature exceeding 10 000 K leads to pronounced plasma absorption via photoionization. Plasma absorption via inverse bremsstrahlung is determined to be negligible because of a relatively low electron density, measured to be peaked at ∼5 X 1018 cm-3.