Measurements of Laser-Induced Plasma and Optical Breakdown Spectra of Aluminium

Abstract

Time‐resolved spectroscopy is utilized in investigations of laser‐induced optical breakdown plasma. Atomic and molecular features are analyzed for diagnostics applications in laser materials processing. The micro‐plasma that is generated by nominal 1 to 10 nanosecond, focused laser radiation shows Stark broadened and shifted atomic lines early in the plasma decay. Subsequently, the emissions from the plasma reveal molecular recombination spectra. Analysis of the spectroscopic features allows one to infer species number densities and temperature. Measured spatial characteristics and post‐breakdown fluid physics phenomena are numerically modeled using computational fluid dynamics. Electron number densities as high as 1019 cm−3 are found, determined from Stark widths and Stark shifts of hydrogen Balmer‐alpha line. Stark broadened aluminium line spectra, following optical breakdown of solid aluminium, show electron number densities of typically 0.5 × 1019 cm−3 early in the plasma decay. The electron number densities for the aluminium experiments are inferred by comparison with hydrogen Balmer series lines.