Effects of Preplasma in 10-ps Relativistic Laser Matter Interaction

Experiments were performed using the kJ 10-ps OMEGA EP laser to study the effect of preplasma on fast electron generation and energy coupling in relativistic laser plasma interaction (LPI) with a controlled preplasma at various scalelength created by a 1-ns UV laser. Targets were multilayered planar foil consisting of an Al substrate, a buried Cu layer and a thick conductive CH layer. Preplasma density profile and relativistic LPI generated fields were characterized using a 10-ps 4$\omega$ optical probe (angular filter refractometry and polarimetry) together with radiography using a high-energy proton beam produced by the second kJ 10-ps EP beam. Fast electrons were diagnosed by measuring Cu K-shell fluorescence emission and bremsstrahlung radiation. Electron energy spectrum was monitored by a magnetic spectrometer. Preliminary results showed nonlinear interaction instabilities and a reduced electron temperature with increasing preplasma scalelength. Dynamics of the relativistic LPI and the resultant fast electron beam characteristics and energy coupling will be presented.