Hydrodynamic evolution of picosecond laser plasmas

Abstract

ABSTRACT The density profile evolution of picosecond laser-plasmas has been inferred from the angulardependence of the specular reflectivity of a probe picosecond pulse. Time-resolved density profiles,critical density scale-lengths as short as 3 nm and values for the plasma collisionality are presentedfor a gold target irradiated by a 580 nm, 0.8 p5 FWHM laser pulse with a peak intensity of up to2x1 013Wcm2. The results are best fitted at early times (<10 ps) by the self-similar isothermalexponential density profile and a critical density collision frequency of 0.3w, in good agreement with 1-D hydrodynamic simulations. I . INTRODUCTION The advent of high power, moderate energy and repetition rate picosecond lasers has spurred interest in table-top laser plasma research. Much of the effort has been directed towards producing a uniformsolid density high temperature plasma suitable for diagnosis.13 The difficulties associated with thisare twofold: the laser pulse duration must be short enough for efficient coupling to the solid target