High-Harmonic Probe for Relativistic Laser-Matter Interactions Driven by Ultrashort Pulses in the Mid-Infrared

High-order harmonic generation (HHG) is one of the central effects in strong-field nonlinear-optical physics [1]. Within the past two decades, HHG has been at the heart of a paradigm-shifting breakthrough to attosecond physics [2]. Much less limelight has been given to the ability of HHG to serve as a highly sensitive and in many ways unique analytical tool. When used in this modality, HHG can help detect and understand ultrafast electron dynamics in complex gas-phase, solid-state, and laser-plasma systems [3]. Here, we extend this concept by using HHG as a probe for relativistic laser-matter interactions driven by ultrashort pulses in the mid-infrared.