Application of the Complex Kohn Variational Method to Attosecond Spectroscopy

TL;DR

This paper extends the complex Kohn variational method to calculate light-driven electronic transitions in atomic and molecular systems, enabling detailed study of multiphoton processes in attosecond spectroscopy.

Contribution

The paper introduces a new finite-pulse perturbative approach based on the complex Kohn variational method for simulating multiphoton ionization processes.

Findings

Good agreement with independent simulations for helium ionization spectra.

Demonstrated applicability to two-photon pump-probe spectra near Feshbach resonances.

Paves the way for ab initio studies of weak-field attosecond phenomena in molecules.

Abstract

The complex Kohn 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 several two-photon ionization pump-probe spectra, resonant with the (2s2p)1P1o Feshbach resonance, with independent simulations based on the atomic B-spline close- coupling STOCK code, and find good agreement between the two approaches. This new finite-pulse perturbative approach is a step towards the ab initio study of weak-field attosecond processes in poly-electronic molecules.