Temporal effect on tight focusing, optical force and spin torque of high-order vector-vortex beams

We theoretically study the dependence of the light field distributions, optical force and spin torque of high-order vector-vortex (HOVV) beams focused by a high numerical aperture objective on ultrafast variable time (0–400 fs). It is accomplished by the fast Fourier transform, time-dependent vectorial diffraction theory and Rayleigh scattering model. Firstly, it is shown that the light field patterns of tightly focused HOVV beams can be quasi-periodically reshaped by adjusting the intrinsic fleeting time. We further examine the three-dimensional (3D) distributions of optical force on a Rayleigh particle (with a size much smaller than the light wavelength) in the focal volume induced from tightly focused HOVV beams, which reveals that the distinct vector-vortex light fields as a function of ultrafast time endow the capability of the selective trapping for particles. Beyond that, we proceed to the 3D spin torque on the given particle, which makes the conversions between transverse and longitudinal spin torques possible, resulting in the 3D spatial rotation within an ultrafast timescale. Additionally, it is found that the vortex order plays a pivotal role in steering the focused light fields and related optical forces and spin torques. The proposed pathway and acquired results not only provide a novel degree of freedom for the ultrafast control of light fields, but also have potential applications in integrated spectroscopic analysis, ultrafast optical tweezers and spanners, and high-speed optical measurements.