Investigation of ultra-intense laser interactions with long scale length pre-plasmas and nanowire targets via escaped fast electrons

In this thesis the results of two experimental campaigns investigating the performance of novel nanowire targets via escaping fast electrons at the target rear surface are presented. An initial experiment was carried out to diagnose the efficiency of laser interactions with nanowire coated and planar targets using imaging of coherent transition radiation (CTR) emission induced by exiting fast electrons. This experiment was subject to an intense pre- pulse of intensity I ∼ 10 17 W/cm^2 irradiating the targets prior to the arrival of the main laser pulse. Hydrodynamic simulations demonstrate the pre-pulse irradiation launched a shock-wave into the target, disrupting the rear surface of the thinner targets. CTR emission was still observed experimentally from these thinner targets, despite the significant target expansion. Particle-in-cell simulations are used to show the scale length of the density disruption was short enough to retain the efficient production of CTR emission in the optical regime. In addition, the hydrodynamic simulations revealed the formation of an extended pre-plasma at the front surface of the targets. This is predicted to facilitate the generation of super-ponderomotive electrons, beneficial towards the production of CTR. Remarkably, under these non-ideal conditions an increase in CTR emission was observed for a subset of shots on the nanowire coated targets compared to planar targets. This result is explained by proposing a less dense, longer scale length pre-plasma is produced from the nanowires, expediting the production of fast electrons with a greater hot electron temperature.

A subsequent experiment aimed to realise a high contrast laser interaction with nanowires through the use of a frequency doubled laser pulse. In this campaign a pepper-pot diagnostic was employed to measure the emittance of the exiting fast electron beam, a novel measurement for nanowire targets. The results indicate fast electrons with a greater emittance are obtained from the nanowire targets relative to planar targets. Particle-in-cell simulations are carried out that predict a greater transverse momenta of fast electrons from the nanowire targets, supporting this conclusion.