Fabrication, Characterization and Application of High Density Gas Targets for Intense Laser Interaction Experiments

Abstract

We report on the generation and characterization of submillimetric Argon gas jets with peak density higher than 10^21 atoms/cm3 from capillary nozzles of varying throat diameter in the range of 50-450 μm. The use of gas jet targets to generate a suitably dense, reliable, and reproducible interaction medium is particularly important in the broad field of laser-plasma interactions, in areas such as high energy density physics (HEDP), plasma waveguides, electron/ion acceleration and x-ray generation.

Here, it is essential to place those targets in the laser focus with subwavelength accuracy and have control over the gas flow using a sonic or supersonic nozzle to provide the desired interaction density. The use of a sonic or supersonic gas flow provides a Gaussian like or plateau neutral density profile. By changing the gas pressure and temperature, one can change the initial neutral density and by using a combination of gases, one can obtain plasmas with multiple ions species, which is needed to localize electrons injection for innovative laser-plasma accelerator schemes. In this thesis, we present a study of the specific characteristics of gas jets produced by micron-sized nozzles in the context of laser-plasma physics. The study is based on experimental work on gas jets of varying sizes and parameters such as backing pressure and temperature.

The thesis is organized as follows: Chapter 1 examines the motivation for generating such high density gas jets in the context of laser wakefield acceleration and the flow physics of supersonic gas jets. Chapter 2 presents the work in manufacturing the nozzles and characterizing the gas jets produced from the straight capillary nozzles using interferometry methods to measure the density profiles and Rayleigh Scattering to identify clusters in the target. Chapter 3 explores the possible applications of the gas jets in terms of generating gas targets in atmospheric conditions, producing icy filament targets by cooling and demonstrating multi-nozzle arrays.