Application of the Complex Kohn Variational Method to Attosecond Spectroscopy

Abstract

The complex Kohn (CK) variational method is extended to compute light-driven electronic transitions between continuum wavefunctions in atomic and molecular systems. This development enables the study of multiphoton processes in the perturbative regime for arbitrary light polarization. As a proof of principle, we apply the method to compute the photoelectron spectrum arising from the pump-probe two-photon ionization of helium induced by a sequence of extreme ultraviolet and infrared-light pulses. We compare various two-photon ionization pump-probe spectra, resonant with the (2s2p)1P_0 Feshbach resonance, with independent simulations based on the B-spline close coupling STOCK code, and find good agreement between the two approaches. This new finite- pulse perturbative approach is a step towards ab initio study of weak-field attosecond processes in polyelectronic molecules