Controlling light with light via structural transformations in metallic nanoparticles

Reversible light-induced structural transitions in metallic nanoparticles, taking the form of surface-driven dynamic phase coexistences, provide an optical nonlinearity suitable for controlling light with light in nanophotonic and plasmonic switching devices. Using low-power diode lasers (giving excitation powers of a few tens of nanowatts per particle) operating at telecom wavelengths, we studied this nonlinearity in gallium nanoparticles grown from atomic beam at the tip of silica optical fiber. The nonlinear response characteristics indicate the occurrence of both solid-solid and solid-liquid transitions and are consistent with an effective medium model for the optical properties of closely packed nanoparticle films. The megahertz dynamics of light-by-light control in the particle film provide an insight into the kinetics of structural transformations in nanoparticles. Transitions between two solid phases of gallium in the nanoparticles, occurring on application and withdrawal of optical excitation, take considerably less than a microsecond. The transient characteristics of the nonlinearity associated with the solid-liquid transition are dominated by the recrystallization time, which is typically of the order of a microsecond.