Boosted High Order Harmonics from Electron Density Singularity Formed at the Relativistic Laser Bow Wave

TL;DR

This paper demonstrates that relativistic laser bow waves create electron density singularities which reflect and upshift the frequency of incident laser pulses, generating coherent high-order harmonics through particle-in-cell simulations.

Contribution

It introduces a novel mechanism of high-order harmonic generation via electron density singularities at relativistic bow waves in laser plasma.

Findings

Generation of relativistic harmonics up to several times the driver frequency.

Reflection and compression of incident laser pulses at electron density singularities.

Validation through particle-in-cell simulations of the harmonic generation process.

Abstract

We demonstrate coherent hard electromagnetic radiation generation from reflection by the electron density singularity formed at the relativistic bow wave in laser plasma via particle-in-cell simulations. Wake and bow waves driven by an intense laser pulse form an electron density singularity at the laser pulse front where they join. A counter-propagating laser pulse is reflected at the electron density modulations moving with relativistic velocity. The reflected electromagnetic pulse is compressed and its frequency is upshifted. Its frequency spectrum contains relativistic harmonics of the driver pulse frequency generated at the bow wave front, all upshifted with the same factor as the fundamental mode of the incident light.