From ablation to radiation pressure in intense laser–matter interaction

The transition from ablation to radiation pressure with increasing laser intensity in linear polarization is studied in a steady state model. At moderate intensities and laser wavelength λλ up to Iλ2=1015–1016W/cm2μm2 the pressure is determined basically by the hot plasma and its flow dynamics. The contribution of the ponderomotive (radiative) potential to the total pressure is determined by plasma outflow inhibition which causes flow stagnation in the critical region and ablation pressure lowering already at ratios radiation/plasma pressure as low as a few percent. When approaching relativistic intensities the dominance of the ponderomotive pressure leads to a continuous transition from a I2/3 to I1 dependence. The location of this transition is governed by heat conduction into the dense target interior. We attribute the strong deviations of the measured exponents from 23 in the low intensity domain to energy losses also by electron heat flow. Basic features of the model have been tested by particle-in-cell simulations.