Nonlinear Transient Dynamics of Photoexcited Resonant Silicon Nanostructures

Optically generated electron–hole plasma in high-index dielectric nanostructures was demonstrated as a means of tuning their optical properties. However, until now an ultrafast operation regime of such plasma-driven nanostructures has not been attained. Here, we perform pump–probe experiments with resonant silicon nanoparticles and report on dense optical plasma generation near the magnetic dipole resonance with an ultrafast (about 2.5 ps) relaxation rate. On the basis of experimental results, we develop an analytical model describing the transient response of a nanocrystalline silicon nanoparticle to an intense laser pulse and show theoretically that plasma-induced optical nonlinearity leads to ultrafast reconfiguration of the scattering power pattern. We demonstrate 100 fs switching to a unidirectional scattering regime upon irradiation of the nanoparticle by an intense femtosecond pulse. Our work lays the foundation for developing ultracompact and ultrafast all-optical signal processing devices.