Time-dependent quadratic nonlinearity and polarisation control in the epsilon near-zero regime (Keynote Presentation)

Ultrafast nonlinearity which results in modulation of linear optical response is a basis for development of time-varying media, in particular those operating in the epsilon-near-zero regime. Here, we demonstrate that the intraband excitation of hot electrons in the epsilon-near-zero media results in the strong second-harmonic modification while the changes in linear transmission are negligible. We also show that nonlinear response of anisotropic epsilon-near-zero materials can be controlled by coupling to vibrational modes and influences the polarisation of the reflected light.