Time-dependent R-matrix calculations for multiphoton ionization of argon atoms in strong laser pulses

A recently developed [Guan , Phys. Rev. A 76, 053411 (2007)] general ab initio and nonperturbative method to solve the time-dependent Schrodinger equation (TDSE) for the interaction of a strong attosecond laser pulse with a general atom is applied to multiphoton ionization of argon atoms. The field-free Hamiltonian and the dipole matrices are generated using a flexible B-spline R-matrix method, which allows for the use of nonorthogonal sets of one-electron orbitals. The solution of the TDSE is propagated in time using the Arnoldi-Lanczos method. The effects of the pulse length and the laser intensity on the ionization rate for different photon energies are analyzed. In the long-pulse regime, good agreement with predictions from R-matrix Floquet calculations is achieved.