3D optical trapping by a tightly focused circular airy beam

In this Letter, we report on the experimental investigation of three-dimensional (3D) optical trapping by a tightly focused circular Airy beam (CAB). We compare the trapping strength of the beam for 800 nm polystyrene particles, with two equivalent Gaussian beams of the same envelope (SEGB) and the same spot-size (SSGB). Through video microscopy, we found that SEGB is incapable of forming a 3D trap, and particles are pushed along the beam propagation direction, while SSGB and CAB could form stable 3D traps. Measurements of trap stiffness revealed that although both beams have similar lateral trap stiffnesses, interestingly CAB has a 6.6-fold stronger axial trap, owning to its autofocusing nature. Furthermore, we found that trap stiffness at various trapping depths is nearly constant for CAB, in contrast with the Gaussian beam, implying that CAB is robust against spherical aberration.