Optical absorption properties of laser-dressed matter

We develop a theory for the optical absorption of electronic materials driven far from equilibrium by resonant and non-resonant lasers. In it, the interaction between matter and the driving light is treated exactly through a Floquet analysis, while the effects of the probing light are captured to first order in perturbation theory. The formalism is employed to characterize the optical properties of a nanoscale semiconductor dressed by non-resonant light of intermediate intensity (non-perturbative, but non-ionizing). As shown, non-resonant light can reversibly turn this transparent semiconductor into a broadband absorber and open strong absorption/stimulated emission bands at very low frequencies (~meV). These developments offers a platform to understand and predict the emergent optical properties of materials dressed by the electric field of light, and catalyze the design of laser-dressed materials with desired optical properties.