Evanescent vortex: Optical subwavelength spanner

Conventional optical spanners based on free-space focusedvortex beams are very difficult to manipulate subwavelength objects due to thediffraction limit, while optical subwavelength spanners are not explored.Evanescent wave is one potential tool to realize subwavelength trapping. By combiningvortex with evanescent field, we find that the evanescentvortex can function as an optical subwavelength spanner. We investigate the factors that will affect the generation/function of this subwavelength spanner, including numerical aperture and topological charge. Further, by calculating the optical force and potential on the illuminated objects, we have demonstrated that the evanescentoptical vortex field is able to trap 200  nm polystyrene spherical particles and to rotate them around the ring-shaped field at the same time, making it a subwavelength optical spanner. This mechanism can be used as a tool to study the behaviour of very small objects in physics and biology.

Source: Applied Physics Letters - November 9, 2016 Category: Physics Authors: Shengtao Mei, Kun Huang, Tianhang Zhang, Muhammad Qasim Mehmood, Hong Liu, Chwee Teck Lim, Jinghua Teng and Cheng-Wei Qiu Source Type: research