Creating tunable lateral optical forces through multipolar interplay in single nanowires

The concept of lateral optical force (LOF) is of general interest in optical manipulation as it releases the constraint of intensity gradient in tightly focused light, yet such a force is normally limited to exotic materials and/or complex light fields. Here, we report a general and controllable LOF in a nonchiral elongated nanoparticle illuminated by an obliquely incident plane wave. Through computational analysis, we reveal that the sign and magnitude of LOF can be tuned by multiple parameters of the particle (aspect ratio, material) and light (incident angle, direction of linear polarization, wavelength). The underlying physics is attributed to the multipolar interplay in the particle, leading to a reduction in symmetry. Direct experimental evidence of switchable LOF is captured by polarization-angle-controlled manipulation of single Ag nanowires using holographic optical tweezers. This work provides a minimalist paradigm to achieve interface-free LOF for optomechanical applications, such as optical sorting and light-driven micro/nanomotors. It is a significant challenge to create an interface-free lateral optical force under the illumination of a single polarized plane wave. Here, the authors provide a minimalist paradigm to address this challenge by exploiting multipolar interplay in a single elongated particle.

Automated summary

This study reports a general and controllable lateral optical force in a nonchiral elongated nanoparticle illuminated by an obliquely incident plane wave. The magnitude and direction of the force can be tuned by multiple parameters of the particle and light. Experimental evidence of switchable lateral optical force is provided. This work has significant implications in optomechanical applications.