Ray optics analysis of optical forces on a microsphere in a (2 + 1)D Airy beam

Shuhe Zhang, Jinhua Zhou, and Yu-Xuan Ren

The optical forces of a (2 + 1)D Airy beam on a microsphere are studied in the ray optics regime. The ray model of a (2 + 1)D Airy beam is derived from its Fourier angular spectrum using a stable aggregate of the flexible elements theory. Numerical results demonstrate that the microsphere can be trapped by the transverse optical force and pulled towards the beam major lobe. Longitudinal optical forces further push the microsphere towards the positive z-direction. The trend for the movement of a microsphere in an Airy beam is clearly demonstrated as the stream line of optical forces, which is consistent with the observed phenomena in optical trapping experiments. In the meantime, both the transverse and the longitudinal optical forces increase when the relative refractive index of the trapped microsphere increases. Calculation of optical forces on microspheres with larger size reveals that the optical forces contributed by rays on each hemisphere are actually different due to the asymmetry of the Airy beam. The force difference could cause natural torque on the trapped objects if they are ovals or other asymmetric shapes.

DOI