High harmonic interferometry of the Lorentz force in strong mid-infrared laser fields

TL;DR

This paper demonstrates a method using two non-collinear circularly polarized laser beams to control and cancel the Lorentz force in high harmonic generation, enabling recollision processes in strong mid-infrared fields.

Contribution

It introduces a novel optical setup with opposite circular polarizations to monitor and mitigate the Lorentz force effects in high harmonic generation.

Findings

Controlled recollision processes enabled beyond the dipole approximation

Lorentz force effects can be canceled using ellipticity from two beams

Observation of the dipole approximation breakdown in high-harmonic generation

Abstract

The interaction of intense mid-infrared laser fields with atoms and molecules leads to a range of new opportunities, from the production of bright, coherent radiation in the soft x-ray range to imaging molecular structures and dynamics with attosecond temporal and sub-angstrom spatial resolution. However, all these effects, which rely on laser-driven recollision of an electron removed by the strong laser field and the parent ion, suffer from the rapidly increasing role of the magnetic field component of the driving pulse: the associated Lorentz force pushes the electrons off course in their excursion and suppresses all recollision-based processes, including high harmonic generation, elastic and inelastic scattering. Here we show how the use of two non-collinear beams with opposite circular polarizations produces a forwards ellipticity which can be used to monitor, control, and cancel the effect of the Lorentz force. This arrangement can thus be used to re-enable recollision-based phenomena in regimes beyond the long-wavelength breakdown of the dipole approximation, and it can be used to observe this breakdown in high-harmonic generation using currently-available light sources.