Noncollinear harmonic spectroscopy reveals crossover of strong-field effects

Abstract

<p>The ability to control electron motion with light fields represents a transformative frontier in modern physics, enabling dynamic manipulation of material properties at ultrafast timescales. Yet, the complex interplay between light and excited carriers—via mechanisms such as the AC Stark effect, field-induced coupling of excitonic and Bloch states, the dynamical Franz-Keldysh effect, and the ponderomotive effect—continues to challenge our understanding of quantum systems driven far from equilibrium. Here, we establish non-collinear harmonic spectroscopy as a powerful technique for initiating, tracking, and steering femtosecond carrier dynamics across the energy landscape in the dielectric SiO₂ crystal. Combining rigorous numerical simulations with analytical theory, we identify the main mechanisms responsible for the crossover of different strong-field phenomena, which leads to the delay-dependent energy shift of excitonic and Bloch states. This control over the electronic and excitonic states opens new opportunities for tailoring carrier dynamics in quantum materials, paving the way for next-generation optoelectronic and nanophotonic technologies.</p>