Propagation and evaluation of lateral linear momentum of optical vortices

The angular momentum distributions and their propagation evaluation characteristics of optical vortices, especially vortices with the complicated topological structure, which are difficult to measure accurately through an experiment, can be obtained by numerical computation. The lateral linear momentum density of optical vortices is obtainable by neglecting the longitudinal component of linear momentum density of linearly polarized optical field, and the angular momentum distribution is characterized by the azimuth component of lateral linear momentum density. The propagations of a single Laguerre-Gaussian beam and a vortex beam superimposed by two Laguerre-Gaussian beams with different topological charges are numerically simulated in free space. Through the simulation, the transverse profiles of intensities, phases, and lateral linear momentum density in Rayleigh range are obtained. It is shown that the lateral linear momentum density is reduced, and that simultaneously the radial component of linear momentum is increased due to the beam diffraction. Consequencely, the radial mechanics is enhanced and the azimuth one is abated. Therefore, the beam cross sections which are far away from the beam waist are not suitable to be utlized for the manipulation of microparticles.