Broadband unidirectional scattering in the transverse direction and angular radiation realized by using a silicon hollow nanodisk under a radially polarized beam

In recent years, directional scattering has been one of the most active research hotspots in the field of nanophotonics. Herein, we study the directional scattering properties of a silicon hollow nanodisk illuminated by a tightly focused radially polarized beam. The induced strong longitudinal total electric dipole interferes with transverse magnetic dipole to achieve a highly-efficient transverse unidirectional scattering when the silicon hollow nanodisk is located at a specific position in the focal plane. Moreover, the manipulated unidirectional scattering in the transverse direction can be realized in the broad wavelength range from 581 nm to 656 nm. In addition, the unidirectional angular radiation towards all directions can be realized by adjusting the position of the silicon hollow nanodisk. Our research results are helpful for the design of nanophotonic devices that can manipulate the angular radiation direction, and have potential applications in sensing, optical communications, solar cells and other fields.

Optimized anti-reflection core-shell microspheres for enhanced optical trapping by structured light beams

In this paper, we study the optical trapping of anti-reflection core-shell microspheres by regular Gaussian beam and several structured beams including radially polarized Gaussian, petal, and hard-aperture-truncated circular Airy beams. We show that using an appropriate anti-reflection core-shell microsphere for the optical trapping by several structured light beams can dramatically enhance the strength of the trap compared to the trapping by the common Gaussian beam. The optimal core-shell thickness ratio that minimizes the scattering force is obtained for polystyrene-silica and anatase-amorphous titania microspheres, such that the core-shells act as anti-reflection coated microspheres. We show that the trapping strength of the anti-reflection coated microparticles trapped by the common Gaussian beam is enhanced up to 2-fold compared to that of trapped uncoated microparticles, while the trapping of anti-reflection coated microparticles, by the radially polarized beam, is strengthened up to 4-fold in comparison to that of the trapped uncoated microparticles by the Gaussian beam. Our results indicate that for anatase-amorphous titania microparticles highest trap strength is obtained by radially polarized beam, while for the polystyrene-silica microparticles, the strongest trapping is achieved by the petal beam.