Our paper on the optical properties of laser-driven matter is published in Phys. Rev. A. In this work, we develop a theory of optical absorption that is valid for non-equilibrium systems, in particular, laser-driven systems. We applied this theory to investigate the emergent optical absorption properties of a nanoscale semiconductor driven by a intense non-resonant light. It turns out that the optical absorption properties of a laser-driven matter is qualitatively different from the pristine material. Depending on the strength of the dressing light, it can generates replicas of absorption bands that are separated by integer number of photon energies, and generates absorption/emission signals at THz regime.