Coherent Vortices Properties of Partially Coherent Elegant Laguerre-Gaussian Beams in the Free Space

Miao Dong,Yuanjie Yang

doi:10.4236/opj.2020.106017

Abstract

The analytical expression of the cross-spectral density of partially coherent elegant Laguerre-Gaussian beams propagating in free space has been derived. The coherence vortex properties of such beams have been investigated. The effect of the beam parameters, including the topological charge, radial mode index and coherence length on the coherent vortex, is analyzed. The results show that the higher order (lth) of coherent vortices split to lth first order of coherent vortex. New coherent vortices of opposite sign appear, and then pairs of coherent vortices form. The propagation distance and coherence length affect the generation of coherent vortices, while the radial mode index doesn’t affect the coherent vortices. These results might be helpful for potential application of such beams in optical communication.

Highlights

Vortex beam has been widely studied due to its special properties [1] [2], such as the helical phase structure, the phase singularity, the dark hollow area and the orbital angular momentum
The analytical expression of the cross-spectral density of partially coherent elegant Laguerre-Gaussian beams propagating in free space has been derived
The results show that the higher order of coherent vortices split to lth first order of coherent vortex

Summary

Introduction

Vortex beam has been widely studied due to its special properties [1] [2], such as the helical phase structure, the phase singularity, the dark hollow area and the orbital angular momentum. This makes it difficult for studying vortex beam with low coherence. It was shown that there exist phase singularities of the spectral degree of coherence of the field at pairs of points. Such phase singularities are termed as “coherence singularities”. Further investigation showed that the phase of spectral degree of coherence possesses a vortex structure around these singular points [9]. The new term “coherence vortices” is used to refer to them These findings reveal that the vortex structure of partially coherent vortex beam is just “hidden” in the correlation function. The effect of topological charge, radial mode index and coherence length on the coherent vortices have been analyzed

Coherence Vortex of Partially Coherent eLG Beams

Numerical Simulation

Conclusion