Evolution dynamics of optical angular momentum and torque through a birefringent metallic subwavelength aperture

Abstract

The interaction of light and matter results in the transfer of linear momentum and angular momentum (AM) which induces optical force and torque, respectively. It is revealed that the linear momentum and AM are conserved for a system of matter and electromagnetic field. In this paper, we present a waveguide-mode analysis to show the dynamic evolution rules for both longitudinal and transverse angular momenta in a metallic subwavelength aperture with different symmetries. In addition, we demonstrate the relationship between AM and optical torque that is based on the AM conservation of light and the metallic subwavelength aperture. Accompanying with the change of AM is the existence of non-zero optical torque, which is promising for dynamic optical manipulation in nanoscale. We believe that unveiling such phenomenon is conducive to the further development of the angular-momentum-based optical mechanics in subwavelength aperture.