Time-varying optical spin-orbit Hall effect in tightly focused femtosecond optical field.

The spin-orbit Hall effect (HE) is dominated by the law of conservation of angular momentum of a beam and is highly significant in light-matter interactions. The electromagnetic field, phase, topological structure, and spin-orbit HE of an azimuthally polarized vortex pulse beam in a tightly focused system are studied theoretically here. Calculations show that the focal field has ultrafast bright-dark alternating characteristics and a distorted phase distribution. Furthermore, the time evolution of the polarization singularity in the focused light field is explained using Stokes parameters. Importantly, the spin-orbit HE of the pulsed beam is shown to be time-varying in a tightly focused system. This time-varying spin-orbit HE is particularly sensitive to the pulse width and central wavelength. Our method has important applications in particle manipulation.