Optical Pulling Force Arising From Nonparaxial Accelerating Beams

We study the optical forces experienced by a dielectric microsphere placed in a nonparaxial vector self-accelerating beam. Following the beam's peak intensity (or the main lobe), where the dominant transverse trapping appears, the longitudinal optical force is found to switch from a purely pushing case to an impure case involving pulling forces. The pulling forces tend to appear away from the optimal transverse trapping position, particularly for large particles but populate largely within the transverse trapping potential. In terms of magnitude, such forces can be comparable to the transverse ones when manipulating small particles. The cases of both Mie and Rayleigh particles are discussed. Our work opens the possibility to uncover the pulling effect in nonparaxial accelerating beams, which may lead to applications in optical trapping and manipulation.