Dual-plane multiple-trapping by tightly focused petal-like circular Airy beam in an aqueous medium

Abstract

Superposition of two circular Airy vortex beams (CAVB), with opposite sign topological charges (l), produces a new type of petal beam called petal-like circular Airy beam (PCAB) with a transverse field distribution in the form of azimuthally modulated concentric rings that follow Airy function over the radial distance on a transverse plane. In this paper, tight focusing of a truncated PCAB and its application in optical trapping is numerically investigated. It is shown that by adjusting the topological charge, l, and the aperture radius of the focusing objective lens, R, four different trapping configurations can be achieved: a single transverse trap at a single axial position, a multi-trap geometry at a single axial position, two single transverse traps at two positions along the axial direction, and two multi-trap geometries at two different axial positions. It is also shown that the number of trapped particles in the multi-trap configurations is 2l per focal plane, while the number of axial trap positions is determined by the truncation aperture size, R. Moreover, trap stiffnesses and corresponding potential energies for the trapping configurations are presented and discussed. Finally, for a special case of large R and l, it is shown that the focused beam may both guide and traps the particles.