Nonlinear optical interactions are of fundamental significance for advanced photonic applications, but often the nonlinearity magnitude is insufficient. In the past decade, we apply laser scanning confocal microscopy, which is a routine tool in biology but unusual with nanomaterials, to inspect single metallic and semiconductor nanostructures. Via the combination of Mie resonance and coupled photothermal/thermo-optic effects, we discovered 1000- to 100000-fold enhanced nonlinear optical indices over bulk materials. The potential applications include all-optical switch and label-free super-resolution microscopy, based on suppression of scattering, saturation (sub-linearity) and reverse saturation (super-linearity). More recently, we uncovered novel light-matter interactions, such as optical bistability in nano-silicon with record-low Q-factor and footprint, as well as displacement resonance. The latter features that linear scattering efficiency is maximal when the focus is misaligned, thus showcasing a significant reduction of nonlinear response threshold, sign flip in all-optical switching, and spatial resolution enhancement.
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