Modelling of non-LTE atomic physics processes in hot dense plasmas during the interaction with an intense short pulse laser

The implicit 2D3V particle-in-cell (PIC) code developed to study the interaction of intense lasers with matter (Petrov and Davis 2008 Comput. Phys. Commun. 179 868-80; 2011 Phys. Plasmas 18 073102) has been extended to include atomic physics under extreme energy density conditions. The atomic physics model is applied to aluminium. Each ionization stage contains two levels: one ground and one lumped excited state, for which various atomic physics processes such as optical field ionization, collisional ionization, excitation, de-excitation and radiative decay describe the population density. Two-dimensional PIC simulations have been carried out for laser pulses with peak intensity 1 x 1020 W cm(-2), pulse duration 60 fs, spot size 3 mu m and energy 0.75 J interacting with ultrathin (0.2 mu m) Al foil. Radiation emitted during the laser-target interaction is computed by accounting for both bound-bound transitions and bremsstrahlung radiation. We demonstrate that the radiation signature of laser-produced plasma can be used as a complementary tool to other diagnostic techniques used in laser-plasma interactions. Finally, results from the PIC model are compared to equilibrium calculations (Maxwell-Boltzmann and Saha). In the early stages of laser-plasma interactions (< 100 fs) the plasma is far from equilibrium and equilibrium models can not be applied with confidence to model the plasma.