Self-injection in a moderately relativistic LWFA regime

My thesis work is centered on the study of the injection properties of LWFA using gas target with different ionization properties including He an N2. The study is centered on experimental work performed at the Intense Laser Irradiation Laboratory (ILIL) in Pisa where application of LWFA including radiobiology and secondary radiation sources studies are being developed. For the thesis, a moderately relativistic LWFA regime was considered, characterized by a maximum intensity on target of I0=2×10^18W/cm 2 with a normalized vector potential a0 =0.96 and a pulse duration of τ=40fs . In these experimental conditions self-focusing allows the main pulse to remain focused along the entire acceleration length without external guiding. In addition to that, self-focusing also leads to a significant increase of the laser intensity enabling ultrarelativist regime. Background plasma is created via tunneling ionization during the interaction between the laser pulse leading front and the gas targets. The different ionization properties of nitrogen and helium, combined with the strong dependence of laser pulse intensity upon plasma density, produce substantial differences in the accelerated electron bunch properties. Selected experiments designed to identify the role of ionization in the injection mechanism will be described. In addition, a preliminary experimental study of the role of tailored density profile will also be presented.