Morphology-independent general-purpose optical surface tractor beam

Abstract

Optical tractor beams capable of pulling particles backward have garnered significant and increasing interest. Generally, it is easier to push than to pull. Traditional optical tractor beams are limited to free space beams with fairly small forward wavevectors, enabling them to pull selected particles. In this study, we present a comprehensive theory for the optical force exerted by a surface wave (SW) through meticulous analytical and numerical calculations, uncovering the relationship between the canonical momentum and optical forces. Moreover, based on the theory, we demonstrate a general-purpose optical surface tractor beam (OSTB) that can pull virtually any passive particle, regardless of its size, composition, and geometry. The OSTB utilizes a SW with negative canonical momentum characterized by a single well-defined negative Bloch k. Unlike previous cases, it relies on a novel mechanism where the negative incident force always surpasses the recoil force. We demonstrate explicitly that the same OSTB, when excited on the surface of a double-negative-index metamaterial, can pull particles with varying morphologies.