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

Abstract

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-folds 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-folds 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.

Optical trapping and fluorescence control with vectorial structured light

“…Structured beams that reconstruct themselves after being distorted by a trapped particle (Bessel beams) have allowed for trapping in multiple planes 12 , whereas the far-field Bessel beam can be used as an optical shield assisting with trapping in crowded environments 13 . Structured light beams have not only been shown to enhance the trap strength 14 but Airy beams, for example, can guide a particle along a certain trajectory enabling selective removal of particles in a sample 15 , 16 ; with petal beams it is possible to trap particles with different refractive indices simultaneously 17 and frozen waves can increase the stability and 3D control of the trap 18 . The fact that light carries linear momentum is well-known and is the reason why light can trap particles, however, light can also carry orbital angular momentum (OAM), like Laguerre-Gaussian (LG) beams.…”