Manipulation of ultrafast nonlinear optical response based on plasmon-induced magnetic anapole mode.

Ultrafast all-optical switches are pivotal for advancing future optical communication and computing technologies. Plasmonic nanostructures, renowned for inducing strong Kerr nonlinear effects, have emerged as promising platforms for such devices. However, Kerr-type switches inherently face a trade-off between switching speed and modulation depth, posing a formidable challenge for their concurrent optimization. Herein, we propose a theoretically designed system comprising gold ellipsoid arrays, silica spacers, and gold films. This configuration achieves enhanced modulation depth by exploiting the strong optical confinement enabled by a magnetic anapole mode. Concurrently, the switching time is optimized through accelerated electron thermal equilibration via diffusion-mediated heat transport in hotspot regions. By systematically analyzing the spatiotemporal dynamics of electron temperature under varied pump wavelengths, we reveal the fundamental physical mechanisms underlying this performance enhancement. The proposed platform not only provides critical insights for ultrafast all-optical switching but also holds significant promise for advancing nanophotonic devices in optical information processing.