Generation and Propagation of Partially Coherent Power-Exponent-Phase Vortex Beam

Hao Zhang,Chengliang Zhao,A P Konijnenberg,Yangjian Cai,Xingyuan Lu,Haiyun Wang,Zhuoyi Wang

doi:10.3389/fphy.2021.781688

Abstract

We report on a partially coherent power-exponent-phase vortex beam (PC-PEPV), whose spatial coherence is controllable and the initial phase exhibits a periodic power exponential change. The PC-PEPV beam was generated experimentally with various spatial coherence widths, and its propagation properties were studied both numerically and experimentally. By modulating the topological charge (TC) and power order of the PC-PEPV beam, the structure of the vortex beam can be adjusted from circular to elliptic, triangular, quadrangle, and pentagon. When the power order is odd, the PC-PEPV beam with a negative TC can be generated, and the profiles of the PC-PEPV beam can be precisely controlled via adjusting the value of the power order. For the case of high spatial coherence width, the number of the dark cores in the polygonal intensity array of the PC-PEPV beam equals the magnitude of the TC. However, when decreasing the spatial coherence width, the dark cores vanish and the intensity gradually transforms into a polygonal light spot. Fortunately, from the modulus and phase distributions of the cross-spectral density (CSD), both the magnitude and sign of the TC can be determined. In the experiment, the modulus and phase distribution of the CSD are verified by the phase perturbation method. This study has potential applications in beam shaping, micro-particle trapping, and optical tweezers.

Highlights

Since it was verified that the optical vortex can carry orbital angular momentum (OAM) [1], it became a research hot spot in the field of light manipulation
The geometry of the generated partially coherent power-exponent-phase vortex beam (PC-power-exponent-phase vortex (PEPV)) beam are elliptic, triangular, quadrangle, and pentagon, respectively, which is specific compared with the conventional vortex beam that has a “doughnut-like” profile
In this case where we have a high initial spatial coherence width, the number of vortices and the geometry of the PC-PEPV beam can be freely modulated via adjusting the values of the topological charge (TC)

Summary

Introduction

Since it was verified that the optical vortex can carry orbital angular momentum (OAM) [1], it became a research hot spot in the field of light manipulation. The conventional optical vortex has a circular intensity profile, which limits its applications To address this problem, various asymmetric and non-canonical models for optical vortices are proposed, providing higher freedom of control, for example, the optical vortex with a 3D freestyle structure [12], the asymmetric Bessel beam [13], remainder-phase optical vortex [14], Partially Coherent Power-Exponent-Phase Vortex Beam anomalous optical vortex [15], and power-exponent-phase vortex (PEPV) [16]. A new kind of PEPV (NPEPV) beam was proposed, where each part of the spiral phase increases from 0 to 2π, showing exponential growth [21]. The phase and intensity patterns both show rotational symmetry These excellent studies are only focused on the field of fully coherent light

Methods

Results

Conclusion