Gauge invariance of the strong field approximation

TL;DR

This paper demonstrates that the strong field approximation (SFA) can be formulated in a gauge-invariant way at each order of expansion without partitioning the Hamiltonian differently in various gauges.

Contribution

The authors present a gauge-invariant formulation of SFA that avoids the need for multiple Hamiltonian partitions across gauges.

Findings

SFA can be made gauge invariant order by order.

No need for different Hamiltonian partitions in various gauges.

Provides a consistent theoretical framework for SFA.

Abstract

It is shown that strong field approximation (SFA) can be formulated in a gauge invariant manner order by order of the expansion with no need for various partitions of the Hamiltonian in different gauges.