Generalized gauge-invariant formulations of the strong-field approximation

TL;DR

This paper investigates the gauge dependence in the strong-field approximation for atomic and molecular systems under intense lasers, demonstrating that proper partitioning ensures gauge invariance of the S-matrix expansion.

Contribution

It introduces a generalized gauge and partitioning scheme that guarantees gauge invariance in the strong-field approximation.

Findings

Proper partitioning aligns different gauges to produce identical S-matrix expansions.

The gauge problem in SFA is resolved by a suitable choice of partitioning.

The approach enhances the theoretical consistency of SFA in intense laser physics.

Abstract

The gauge problem in the so-called strong-field approximation (SFA) describing atomic or molecular systems exposed to intense laser fields is investigated. Introducing a generalized gauge and partitioning of the Hamiltonian it is demonstrated that the S-matrix expansion obtained in the SFA depends on both gauge and partitioning in such a way that two gauges always yield the same S-matrix expansion, if the partitioning is properly chosen.