Dynamical symmetries in laser harmonic generation via a cubic nonlinearity

TL;DR

This paper explores how dynamical symmetries in laser-target configurations can be used to analyze and predict harmonic generation spectra, connecting symmetry principles with existing diffraction and wave theories.

Contribution

It introduces a symmetry-based framework for understanding harmonic generation, reconciling it with the beat wave approach and classical wave diffraction theories.

Findings

Symmetry analysis reproduces previous harmonic spectrum results.

Connections established between symmetry methods and diffraction theories.

Framework applicable to various literature examples.

Abstract

In our earlier work on harmonic generation with complex light [Nature Communications 15, 6878 (2024)], we demonstrated how the harmonic spectrum of a complex laser beam in a nonlinear medium can be obtained through the judicious application of the ``beat wave'' concept. In this paper, we show how the same results can be obtained via the full set of symmetries of the initial laser-target configuration, and how this can be reconciled with the ``beat wave'' approach. We also highlight the connections between our work and existing theory for diffraction of EM waves from crystals: Laue equations, Mathieu equation, and theorems by Noether, Floquet and Bloch. The specific nature of our approach to harmonic spectra allows these connections to be revealed. We illustrate this with numerous examples taken from existing literature to show the wide applicability of our approach.