Extended Drude Model for Intraband-Transition-Induced Optical Nonlinearity

Optical nonlinearity due to intraband transitions (which is important for the application of epsilon-near-zero nonlinearity in metasurfaces and active plasmonics) requires a model to fully predict the spectrum, for design considerations. The extended Drude model, presented here, serves this purpose. It further elucidates the origin of the nonlinearity to be due to both band nonparabolicity and temperature-dependent mobility. The model matches experiment well for the representative compound indium tin oxide, and simplifies the description of spectrally resolved optical nonlinearities of transparent conductive oxides.