By employing the angular spectrum representation, we successfully derive the partial-wave expansion coefficients of the circular Airy beams (CABs) with different polarizations, based on which the scattering of a spherical particle in the CABs is solved exactly. Special attention is focused on exploring the potential applications of the CABs in the abruptly autofocusing (AAF) property and optical manipulation of microparticle by optical force. It is found that both the linear and circular polarizations are the best candidates to implement the AAF property robustly against strong disturbance by a large-sized particle. In addition, although the CABs can be intensively focused to a small region, resulting in an abrupt increase of light intensity by two orders of magnitude at the focal point and enabling three-dimensional stable trapping of a Rayleigh particle near the focal point, the usual CABs fail to generate an optical force outweighing the Brownian force to achieve a stable transverse trapping in the region before the focal point. On the other hand, a Mie particle can be confined transversely in the primary ring and accelerated along the curved trajectory of CABs to the focal point, then pushed further all the way through the focal point rather than being trapped therein, and eventually accelerated further along a straight trajectory in the direction of light propagation over 100 wavelengths, due to the weak diffraction characteristic of a morphed Bessel-like beam of CABs. The exotic curved-straight trajectory transport of particles by the CABs may find applications in the case where the transport path is partly blocked.

Based on the generalized Lorenz-Mie theory and Maxwell stress tensor formulism, we calculate the transverse force constant matrix and perform a linear stability analysis on a spherical particle that is subject to negative longitudinal optical force (NLOF) under the illumination of Bessel beams. Phase diagrams with respect to the material parameters are presented, which exhibit the possibility of the appearance of NLOF. From dynamical simulations of the particle performed both in the transverse plane and along the longitudinal direction, an even clearer picture of the realization of stable NLOF is presented. It is shown that, due to rotation induced by the orbital angular-momentum of light, higher order Bessel beams cannot stably confine a particle to the beam center where NLOF occurs in the absence of ambient damping, which largely limits their applications for long-distance, stable, backward particle transportation. On the other hand, zero-order Bessel beams can achieve stable transverse confinement of the manipulated particle and act as an optical tractor beam per se. In addition, for a nonmagnetic particle with relative permeability $\mu =1$, a Bessel beam with transverse electric polarization is more favorable for the realization of NLOF than a transverse magnetic beam. Finally, a brief discussion is also presented of the conditions under which an off-beam-axis particle could be suitable for backward transportation using NLOF.

We demonstrate a magnetically controllable nonreciprocal Goos-Hänchen (GH) shift enabled by the magnetic plasmonic gradient metasurfaces (GMSs) consisting of an array of ferrite rods with a rotation gradient introduced to the rod dimers in the unit cell. The incident Gaussian beam is observed to exhibit an evident GH shift about $5\lambda$ when it is incident from one side, whereas for the Gaussian beam incident from the geometrically symmetric direction with respect to surface normal only a very small GH shift comes into appearance. The phenomenon arises from the unidirectional coupling of the incident beam with the magnetic plasmonic GMSs due to the time-reversal-symmetry-breaking nature of the magnetic system as evidenced from the photonic band diagrams of the edge states. The unidirectional GH shift can also be implemented at different incident angles by either engineering the gradient of the GMSs or tuning the bias magnetic field. By designing the magnetic plasmonic GMSs with more exquisite configurations we can expect a lot more nonreciprocal properties, adding additional freedom in manipulating electromagnetic waves.

Based on the Mie scattering theory and Maxwell stress tensor method, we investigate the transverse optical force (TOF) acting on chiral particles illuminated by a zero-order Bessel beam. It is demonstrated that the particle chirality can induce an azimuthal optical force (AOF), resulting in orbital motion of particles around the optical beam axis. The AOF depends strongly on particle loss as well as the handedness of chirality, with its amplitude capable of changing by over an order of magnitude by particle's chiral loss. The other component of TOF, the radial optical force (ROF), is much less sensitive to the magnitude and handedness of the particle chirality as well as the loss when the chirality is small. Analytical result based on dipole approximation reveals that the AOF arises from the direct coupling of particle chirality to both the spin angular momentum (SAM) and optical vorticity (curl of Poynting vector), exhibiting a conversion of optical SAM of an incident beam to mechanical orbital angular momentum of an illuminated particle. Differently, the ROF originates from the transverse gradient force. In addition, particle chirality yields a negative contribution to the gradient force; thus the ROF can be attenuated and even reversed in direction when particle chirality is sufficiently large. These characteristics of TOF might find applications in chirality detection as well as sorting chiral particles of different handedness and separating them from conventional ones.

We demonstrate that a lateral optical force (LOF) can be induced on paired chiral nanoparticles with opposite handedness under the illumination of a linearly polarized plane wave. The LOFs on both chiral particles are equal and thus can move the pair sideways, with the direction depending on the separation between two particles, as well as the handedness of particle chirality. Analytical theory reveals that the LOF comes largely from the optical potential gradient established by the multiple scattering of light between the paired particles with asymmetric chirality. In addition, it is weakly dependent on the material loss of a particle, a feature of gradient force, while heavily dependent on the magnitude and handedness of particle chirality. The effect is expected to find applications in sorting and separating chiral dimers of different handedness.

We derive an analytical expression of the optical torque (OT) on chiral particles in generic monochromatic optical fields within the dipole approximation. Besides the extinction terms owing to the interaction between the dipoles excited on the particle and the incident field, our expression includes also some long missing terms that are understood as recoil due to the radiation of the dipoles excited on the particle. The recoil terms are shown to have a significant contribution to the OT in many situations. Inspired by our expression, we further proved that the net OT vanishes for a lossless isotropic chiral spherical particle of any size illuminated by arbitrary monochromatic optical fields. Finally, we trace the origin of OT on a small chiral sphere immersed in a zeroth-order vector Bessel beam, taking advantage of our analytical expression. It is found that the azimuthal OT perpendicular to the beam’s propagation direction comes from the transfer of the spin angular momentum of the incident field to the particle, while the longitudinal OT along the illumination direction originates from the particle chirality, which generates longitudinal angular momentum on the optical beam and thus makes the particle subject to a longitudinal OT by recoil. Thus the longitudinal OT tends to rotate the chiral particle with opposite helicities in opposite directions, while the transverse OT shows little dependence on the handedness of particle chirality. Our results may help in understanding OT as an extra handle for particle manipulations in optical tweezers.