Visualizing lateral optical force through surface plasmon-coupled emission.

In this Letter, we report the intrinsic relationship among surface plasmon polaritons, lateral optical force, and surface plasmon-coupled emission. The spin-orbit coupling in the near field through circularly polarized beams would lead to the unidirectional excitation of surface plasmon polaritons, where the symmetry state of the electromagnetic field on the surface is broken. This asymmetric scattering would generate the counter-intuitive lateral optical force due to momentum conservation. As the inverse process of surface plasmon polaritons, surface plasmon-coupled emission enables the guide of the near-field surface plasmon polariton signal to the far field. We found that the lateral optical force produced by the unidirectional excitation of surface plasmon polaritons can be observed in the surface plasmon-coupled emission patterns. The elliptical dipole model was used to demonstrate these coupling processes. The magnitude and direction of lateral optical force can be a dipole, respectively. Moreover, the intensity convergence degree and direction of the surface plasmon-coupled emission distribution can reflect the magnitude and direction of lateral optical force, respectively. This work has great potential in the applications of weak force measurement, dynamic optical sorting, and light-matter interaction research.