Analysis of phase change of Laguerre-Gaussian vortex beam during propagation

In order to study the phase characteristics of Laguerre-Gaussian vortex beam during propagation, the vortex beam was obtained by means of spiral phase plates. Based on Fresnel diffraction integral formula, the phase change of the beam in the propagation process and the stability of vortex beam phase singularities at integer order and fractional order were studied by theoretical derivation and numerical simulation. When the beam was transmitted a certain distance, phase contours of the light field on the observation plane became from diverging rays into petal-shaped arcs. The results show that if topological charge of the vortex beam is integer order, the phase singularity of the beam assumes stability in the propagation process. The phase singularity of fractional order is unstable, intensity distribution on the observation plane is obvious asymmetric and the central darkness gradually disappears. The research results supply theoretical foundation and practical guidance for the application of optical micro manipulation and information coding techniques.