Ultrashort - high intensity laser matter interaction studies

Synopsis My thesis work concerns the study of plasmas produced by high intensity lasers (IL 1014 W/cm2). More precisely, it addresses the study of the properties of strongly compressed materials (equations of state - EOS - in regimes of pressures of tens of Mbar). I have tried to address the physics of laser-plasma interactions in a comprehensive way, emphasizing the correlation between various phenomena. The theoretical part is based on a monodimensional analytical description of the plasma created by direct laser irradiation of the target. Such description takes into account the absorption of laser light, the transport of energy and the plasma hydrodynamics. The various regions of the produced laser plasmas are dealt in details: the plasma corona characterized by a very low density of the expanding plasma, the conduction region between the plasma corona and the shocked material, the region compressed by the shock. In this way, I could also estimate the shock pressure (identified with the ablation pressure). The experimental part is mainly devoted to the study of EOS of low density plastic materials (foams). The measurements, which are presented, are of interest because this kind of material may have important applications in experiments with shock waves (ICF, EOS) and for improving the hydrodynamic behaviour of the plasma. These were the first measurements performed at pressures higher than 3 Mbar for such low densities (~ 100 mg/cm3). I also present other experiments in my thesis, one of which is the "Polarimetric detection of laser induced ultra-short magnetic pulses in overdense plasma". This part was performed during a 6 months visit at Tata Institute of Fundamental Research in Mumbai, India. The interaction of intense (~1016 Wcm-2), sub picosecond pulses with solid targets can generate highly directional jets of hot electrons. These electrons can propagate in the solid along with the counter propagating return shielding currents. The spontaneous magnetic field that is generated by these currents, captures in its time evolution, important information about the dynamics of the complex transport processes. By using a two pulse pump-probe polarimetric technique the temporal evolution of multi megagauss magnetic fields is measured for optically polished BK7 glass targets, each coated with a thin layer of either copper or silver. A simple model is then used for explaining the observations and for deducing quantitative information about the transport of hot electrons.