Direct calculation of inverse-bremsstrahlung absorption in strongly coupled, nonlinearly driven laser plasmas

Inverse-bremsstrahlung absorption in strongly coupled plasmas produced by high-intensity lasers is studied numerically. The simultaneous presence of high density and intensity makes it difficult to treat this problem with standard methods. A technique for modeling collisional plasmas is demonstrated which uses a hierarchical tree code---an accelerated molecular dynamics algorithm with an N log N computation time---adapted to model periodic, non-equilibrium two-component plasmas. Good agreement is found with standard theoretical results for classical, weakly coupled plasmas. In a series of further simulations, the dependence of the inverse-bremsstrahlung absorption coefficient on plasma coupling parameter, laser frequency, and the ratio of quiver to thermal velocity v₀/vₜₑ is computed. An important outcome of this study is that the Langdon effect---a change of the velocity distribution function due to an imbalance of heating and equilibration rates---is verified in a direct microscopic particle simulation.