Transient Second-Order Optical Nonlinearity Induced by Hot-Electron Transport

Second-order optical effects are essential to the active control of light and the generation of new spectral components via nonlinear processes such as second-harmonic generation, sum/difference harmonic generation, Pockels effect, and optical parametric oscillation. The portfolio of Chi-2 media, however, is rather limited as the inversion symmetry in most optical materials prevents achieving a non-trivial Chi-2 response, under the electric dipole approximation. It is a long-standing challenge and pressing need to address this fundamental constraint and enable second-order nonlinearities in semiconductors and oxides that dominate the optoelectronics arena. Here, we present a new scheme for breaking the inversion symmetry and enabling Chi-2 processes via the generation and transport of hot electrons. The sub-picosecond kinetics of hot carriers enables the ultrafast conversion of statically-passive oxides into transient second-order nonlinear media, immediately expanding the portfolio of Chi-2 materials beyond the family of conventional nonlinear crystals. In addition, the proposed scheme could be considered as a nonlinear optical probe to monitor the dynamics of interfacial charge transport in hybrid metal/dielectric material platforms.