Numerical studies of light-matter interaction driven by plasmonic fields: the velocity gauge

TL;DR

This paper develops a velocity gauge formulation for light-matter interactions driven by plasmonic fields, demonstrating its equivalence to the length gauge in high-order harmonic generation simulations and discussing numerical efficiency.

Contribution

It introduces a velocity gauge approach from first principles for plasmonic field interactions and compares it with the traditional length gauge in HHG modeling.

Findings

Velocity and length gauges produce equivalent HHG spectra.

Velocity gauge offers potential numerical advantages.

Theoretical validation of gauge equivalence in plasmonic fields.

Abstract

Theoretical approaches to strong field phenomena driven by plasmonic fields are based on the length gauge formulation of the laser-matter coupling. From the theoretical viewpoint it is known there exists no preferable gauge and consequently the predictions and outcomes should be independent of this choice. The use of the length gauge is mainly due to the fact that the quantity obtained from finite elements simulations of plasmonic fields is the plasmonic enhanced laser electric field rather than the laser vector potential. In this paper we develop, from first principles, the velocity gauge formulation of the problem and we apply it to the high-order harmonic generation (HHG) in atoms. A comparison to the results obtained with the length gauge is made. It is analytically and numerically demonstrated that both gauges give equivalent descriptions of the emitted HHG spectra resulting from the interaction of a spatially inhomogeneous field and the single active electron (SAE) model of the helium atom. We discuss, however, advantages and disadvantages of using different gauges in terms of numerical efficiency.