Investigating Total Charge Liberation From Low Intensity Laser Ablation of Solid Targets

Abstract

Measurements of the total charge liberated by laser ablation near the photoemission/plasma production intensity threshold are presented in this thesis. These data are necessary to benchmark theoretical descriptions of laser ablation phenomena in the difficult-to-model threshold intensity regime. The total charge expelled from laser irradiated metallic surfaces is determined from voltage pulses created when a replacement current neutralizes the ablated surface via a well characterized detection circuit. Repeated measurements are made for a laser beam of a known wavelength, energy, pulse duration, and intensity on target. The total net ablated charge is investigated by substituting metallic targets and varying laser parameters. A simplified discrete-element circuit model is used to describe the observed voltage pulses and determine the charge emitted from the laser irradiated surface. Single-shot and multishot measurements are also presented which indicate how laser repetition rates affect the emitted charge.