Creation and spatial-temporal characterization of gas targets and plasmas for laser-electron acceleration

Abstract

The acceleration of electrons by lasers is a technique that has been gaining importance all over the world in recent years due to its potential to decrease the size and complexity of accelerators, favoring the diffusion of this technology to conventional laboratories, with the inevitable emergence of new science and applications. The High Intensity Ultrashort Laser Pulses Laboratory at IPEN has been working to implement the first laser-electron acceleration infrastructure in Brazil and Latin America. For this purpose, we are currently focusing efforts on different challenges, ranging from the creation and characterization of micrometric gaseous targets and laser-induced plasmas for particle acceleration, to the upgrade of a laser system to achieve the needed peak powers. This PhD thesis explores a significant portion of these challenges, starting with the fabrication of micrometric de Laval nozzles by ultrafast laser micromachining in alumina, to generate laser targets in the form of supersonic gas jets in vacuum. Nozzles were manufactured in a home-built trepanning setup, and their geometry and surface quality dependence on the laser and machining parameters were studied, resulting in fabrication protocols that create de Laval nozzles capable of generating supersonic jets used as targets for laser-plasma interactions. To diagnose the micro-jets and the plasmas, a time-resolved Mach-Zehnder-like interferometer was developed, built, and coupled to a pump-probe setup to study the plasma dynamics with femtosecond resolution. In this setup, density profiles of gas jets and laser-induced plasmas were measured with a spatial resolution of a few micrometers. In addition, a detailed study of the laser-induced plasma evolution in air was conducted from tens of femtoseconds to hundreds of picoseconds, in which plasma formation, impact ionization, and electron recombination were investigated, using algorithms and softwares developed by our group. This diagnostic setup proved to be reliable to characterize the density gradients of micrometric laserinduced plasmas, becoming a permanent setup for further laser-electron acceleration developments at IPEN.