  Ultrafast nonlinear optical phenomena in solids have been attracting major
interest as novel methodologies for femtosecond spectroscopy of electron
dynamics and control of material properties. Here, we theoretically investigate
strong-field nonlinear optical transitions in a prototypical two-dimensional
material, hBN, and show that the k-resolved conduction band charge occupation
patterns induced by an elliptically-polarized laser can be understood in a
multi-photon resonant picture; but remarkably, only if using the Floquet
light-dressed states instead of the undressed matter states. Consequently, our
work establishes a direct measurable signature for band-dressing in nonlinear
optical processes in solids, and opens new paths for ultrafast spectroscopy and
valley manipulation.
