Ultrafast Control of Material Optical Properties via the Infrared Resonant Raman Effect

The Raman effect -- inelastic scattering of light by lattice vibrations (phonons) produces an optical response closely tied to a material's crystal structure. Here we show that resonant excitation IR and phonons gives rise can induce giant shifts the refractive index new constants are forbidden in equilibrium We complete description light-matter interactions mediated coupled crystalline insulators currently focus numerous experiments aiming dynamically control material properties including forgotten pathway through nonlinear polarizability. Our work expands toolset for development technologies revealing absorption within terahertz gap enable materials over broad frequency range.