Optical pulling of Mie particles along a curved path by optical scattering forces.

Optical pulling along straight trajectories has been successfully demonstrated for both dipolar and Mie particles using optical gradient and/or scattering forces over the past decade. However, much less attention is devoted to the pulling along curved paths, particularly for Mie particles, since the mechanism of continuous attraction based on intensity gradients is effective only for dipolar particles, thus limiting its practical applications. Here, we demonstrate the optical pulling of Mie particles with gain along a parabolic trajectory immersed in a two-dimensional vector Airy beam.

Interception force assisted optical pulling of a dipole nanoparticle in a single plane wave.

The optical pulling force is generally believed to originate from the recoil force due to the simultaneous excitation of multipoles in the particle, which overcomes the interception force contributing to the optical pushing force. However, we show that the interception force can induce optical pulling force on a small isotropic spherical particle with gain in a uniform electromagnetic plane wave, in which multipole excitation is negligible within the dipole regime. Based on the multipole expansion theory, a rigorous analytical expression is derived for optical force acting on a spherical particle of arbitrary size and composition illuminated by a single plane wave, regardless of its polarization.