Mapping light-dressed Floquet bands by highly nonlinear optical excitations and valley polarization

Ultrafast nonlinear optical phenomena in solids have been attracting significant attention for their potential in femtosecond spectroscopy and the control of material properties. In this work, we theoretically explore strong-field nonlinear optical transitions in the prototypical two-dimensional material hexagonal boron nitride (hBN), employing time-dependent density functional theory (TDDFT) and model calculations. Our findings reveal that the 𝑘-resolved conduction band charge occupations induced by an elliptically polarized laser can be understood within a multi-photon resonant picture—remarkably, however, only when considering the Floquet light-dressed states instead of the undressed matter states. Our work demonstrates that Floquet dressing affects ultrafast charge dynamics even in response to a single pump pulse, and establishes a direct measurable signature of band-dressing in nonlinear optical processes in solids, opening new avenues for ultrafast spectroscopy and valley manipulation.