Reversal of nonlinear optical forces in a Au-Ag Janus particle

Asymmetric nanostructures in chiral optical fields exhibit rich optomechanical behaviors, yet the influence of nonlinear optical effects on their lateral forces has remained largely unexplored. Here, we demonstrate a power-dependent reversal of the lateral optical force in a Au-Ag Janus nanoparticle under femtosecond chiral excitation. As visualized in simulation results, this force reversal arises from the interplay between the particle's structural asymmetry and a nonlinearity-induced evolution of its plasmonic response. This mechanism for nonlinear force switching provides a degree of freedom for optical manipulation, enabling dynamic and chirality-selective particle control that is inaccessible in the linear regime and opening avenues for reconfigurable optical sorting, micromanipulation, and the development of advanced light-driven nanodevices.