Nonlinear Optical Trapping of Gold Nanoparticles

This paper presents the most complete framework to date for understanding the nonlinear optical trapping of highly absorbing nanoparticles within the dipole regime. Highly absorbing and plasmonic particles garner considerable interest due to their enhanced optical interactions, yet traditional linear theory fails to predict their trapping behavior, particularly in the longitudinal direction. We introduce a more comprehensive theory that incorporates four-wave mixing and two-photon absorption, addressing significant gaps in the current literature. Our research shows TPA to be crucial for longitudinal trapping stability. Furthermore, our findings propose a novel phenomenon of multiple split traps in both saturable absorption and reverse saturable absorption regimes. Our framework extends beyond existing models by including factors such as self-induced back-action and scattering forces, aligning theoretical predictions with experimental observations, and laying a robust foundation for future nonlinear optical trapping and manipulation research.