Controllable optical nonlinearity and ultrafast electron dynamic of epsilon-near-zero materials

The epsilon-near-zero (ENZ) materials have been shown to be as one of the most promising optical materials in recent years. This talk will review our recent studies on the active linear and nonlinear properties of conducting oxide epsilon-near-zero materials in planar and optical fiber platforms. I will discuss the observation of abnormal nonlinear temporal dynamics of hot electrons and enhanced optical nonlinearity in AZO and ITO ENZ thin films under different pump fluences and excitation angles using a degenerate pump-probe spectroscopy technique. I will also discuss the enhanced nonlinear absorption mechanism of ITO near the ENZ region, where the nonlinear absorption is dominated by (i) saturable absorption caused by the conduction band electrons and (ii) three- photon absorption caused by valance band electrons. These studies enrich the fundamental understanding of nonlinear properties on ENZ thin films and will open the path to revolutionary ultra-compact nonlinear optical devices.