Role of angular momentum for atomic scattering in intense laser fields

Abstract

We have used nonperturbative quantum-mechanical close-coupled scattering calculations to investigate inelastic atomic collisions induced by strong laser fields. If a partialwave expansion in molecular total angular momentum states is used for the scattering wave function, the selection rule $\ensuremath{\Delta}J=\ifmmode\pm\else\textpm\fi{}1$ for the radiative interaction matrix elements results in an infinite set of close-coupled equations. Model calculations for the total laser-induced inelastic cross section for both beam and homogeneous-gas experiments are carried out for two $^{1}\ensuremath{\Sigma}$ states coupled by linearly polarized light. A truncated expansion is used with a sufficient number of rotational states to ensure convergence of the cross section. The results show that the exact cross section saturates much more slowly with increasing laser intensity than the cross section calculated for a two-state $J$-conserving model. Angular momentum changes larger than \ifmmode\pm\else\textpm\fi{}1 are possible when the laser intensity is sufficiently high. Thus, a sufficient number of rotational states must be included in the expansion basis to take into account scattering paths that can lead to large changes in angular momentum.