Above-threshold multiphoton detachment from the H- ion by 10.6-μm radiation: Angular distributions and partial widths

Abstract

We present a general procedure for accurate nonperturbative treatment of the angular distribution and partial widths for multiphoton above-threshold detachment (ATD) of atoms or negative ions in intense laser fields. The procedure consists of the following two steps: (1) The resonance wave function is determined by means of the non-Hermitian Floquet Hamiltonian method. The Floquet Hamiltonian is discretized by the complex scaling generalized pseudospectral method recently developed by Yao and Chu [Chem. Phys. Lett. 204, 381 (1993)]. No computation of potential matrix elements is required, and the kinetic-energy matrix elements can be evaluated analytically. (2) The angular distribution and partial rates are calculated, based on an exact differential expression, and a procedure is developed for the backrotation of the total complex resonance wave function to the real axis. The method is applied to the study of multiphoton ATD of H- in strong fields at 10.6 μm. An accurate one-electron model potential [Laughlin and Chu, Phys. Rev. A 48, 4654 (1993)], which reproduces the known H- binding energy and the low-energy e-H(1s) elastic scattering phase shifts, is employed. At this low frequency, the resonance wave functions can be obtained efficiently and rather accurately by means of a nonperturbative adiabatic approach recently developed by Telnov [J. Phys. B 24, 2967 (1991)]. This adiabatic theory is also valid in the limit of weak fields, and its validation is justified by its agreement with the exact perturbation calculations for the seven- and eight-photon detachment of H-. Detailed results for the angular distribution and partial widths for multiphoton ATD of H- are presented for the moderately strong laser intensity regime (1010–1011 W/cm2) at 10.6 μm.