Interaction Of Ultrashort Intense Laser Pulses With Foil Targets And Temporally Resolved Study Of Laser Plasma Channel

We present our work in four parts: (1) Construction of diagnostics in the targetareas of Xtreme LightⅡ(XL-Ⅱ) and Xtreme LightⅢ(XL-Ⅲ) laser systems; (2)Measurements of fast electrons generated in the interaction of ultrashort intense laserpulses with foil targets; (3) Study of the rear-side optical radiation generated by hotelectrons; (4) Temporally and spatially resolved study of laser generated plasmachannel with a streak camera.In the first part, constructions of target area of XL-Ⅲare presented, including thevacuum chamber, vacuum system, fine mechanics and control system, et. al. A laserbeam pointing stabilization system is also built on the XL-Ⅱlaser system.We investigate the interaction of XL-Ⅱlaser pulses with foil targets firstly. Acollimated fast electron beam along the target surface is observed. This resultconfirms directly the guide of fast electrons along the inner surface to the tip in there-entrant cone scheme of fast ignition experiments. The surface fast electrons alsohave potential applications such as laser-based electron source etc. The three mainfactors that affect the generation of surface fast electrons are studied.Secondly, the rear side optical emission is studied in the interaction offemtosecond laser pulses with foil target. The red-shifted second harmonic emissionof the laser light is observed in the laser propagation direction. The emission isattributed to the coherent transition radiation (CTR) generated when the hot electronsaccelerated by the V×B heating process traverse the solid-vacuum boundary. The redshifting results from the expansion of the critical density surface towards the vacuumside. The measurements of the CTR provide a potential diagnostic to the movement ofcritical surface in the laser-plasma interaction process.Thirdly, a long plasma channel is generated in the propagation of intensefemtosecond laser pulses in air. The fluorescence generated by the channel ismeasured temporally and spatially resolved with a streak camera. The ionization front,life time of plasma channel and length of plasma channel are deduced.