Broadband nonlinear optical response of titanium nitride in the visible spectral range

Abstract

Epsilon-near-zero (ENZ) materials, a new class of materials with vanishing permittivity, which can significantly enhance the interaction between incident light and matters. Here, we investigated the third-order nonlinear optical response of titanium nitride (TiN), an ENZ material, in the visible range by using Z-scan method, and obtained a maximum nonlinear absorption coefficient β of −3.78 × 103 cm/GW at its ENZ wavelength. Furthermore, the carriers dynamic characteristics of TiN are revealed by time-resolved pump-probe measurement, including the intraband and interband excitation, the former is mainly derived from laser-induced to form a non-equilibrium distribution of hot electrons, resulting in the electron energy redistribution process in the conduction band, and the latter is the electrons located in the valence band being promoted to the conduction band, increasing the total free carrier density and thus causing a change in the optical properties. Our results indicate the great potential applications of TiN in nonlinear optical and all-optical modulation devices.