Multiphoton detachment of H- near the one-photon threshold: Exterior complex-scaling–generalized pseudospectral method for complex quasienergy resonances

Abstract

We perform a nonperturbative study of the multiphoton above-threshold detachment of H- in the presence of 1.640−μm and 1.908−μm laser fields by means of the non-Hermitian Floquet formalism. The laser parameters used are related to the recent experiments [L. Præstegaard, T. Andersen, and P. Balling (unpublished)] on the two-photon detachment of H- near the one-photon threshold. The total and partial (above-threshold) detachment rates as well as the electron angular distributions are calculated for the laser intensities from 109W/cm2 to 1012 W/cm2. It is found that at the weaker intensities (below 1011 W/cm2), the perturbation theory provides a reasonable description of the two-photon detachment process and the detached electrons are largely in the d state. For higher intensity, however, the process becomes highly nonperturbative in nature. To perform the calculations, we have introduced an exterior complex-scaling–generalized pseudospectral (ECS-GPS) technique for the discretization and solution of the non-Hermitian Floquet Hamiltonian. The ECS-GPS procedure is accurate, simple to implement, and computationally more efficient than the basis-set expansion–variational methods for resonance-state calculations. It also provides a simpler procedure than the uniform complex-scaling method for the calculations of partial rates and electron angular distributions.