Ultraviolet Laser Plasma Preionization and Novel Thomson Scattering Method for Weakly Ionized Discharges

Abstract

The first part of the paper presents initial studies of a dual pulse approach to create controlled laser plasmas in air using preionization. The method utilizes a 266 nm pulsed laser beam to create preionization, followed by a second overlapped 1064 nm pulsed laser beam to add energy. Electron number density measurements, based on a plasma conductivity method, indicate that the 266 nm beam is effective at preionizing the air. The preionization from the ultraviolet pulse is also shown to influence the breakdown threshold of an overlapped 1064 nm laser beam. The second part of the paper presents a novel method for measuring electron density and energy using Thomson scattering. The approach relies upon using a build-up cavity to provide a high power light source (~10-100 kW of average power). Initial modeling results supporting the viability of the approach and showing its potential sensitivity are provided.