Momentum-Topology-Induced Optical Pulling Force
H. Li, Y. Cao, B. Shi, T. Zhu , Y. Geng, R. Feng, L. Wang, F. Sun, Y. Shi, M. Ali Miri, M. Nieto-Vesperinas, C. Qiu, W. Ding
We report an ingenious mechanism to obtain robust optical pulling force by a single plane wave via engineering the topology of light momentum in the background. The underlying physics is found to be the topological transition of the light momentum from a usual convex shape to a starlike concave shape in the carefully designed background, such as a photonic crystal structure. The principle and results reported here shed insightful concepts concerning optical pulling, and pave the way for a new class of advanced optical manipulation technique, with potential applications of drug delivery and cell sorting.
(a) Changes of max[Fx(x, 0)] exerted on different elliptical objects (see the inset). The refractive index varies from 1.4 to 2.6, and the semiaxis rx changes from 0.1 to 1 μm, (ry = 0.1 μm is fixed for convenience). In the colored region, the objects experience continuous pulling forces when they shift along x axis. P1 and P2 are two representative objects analyzed in detail in (b) and (c). (b) Scattered field by the object P1. Because of the symmetry of the structure, only the half space of y > 0 is shown. Forward scattering occurs which generates a continuous pulling force. (c) Scattered field by the object P2. Backward scattering results in a pushing force and cancels the pulling force generated by the forward scattering.