Synthesis of ununiformly correlated radially polarized partially coherent beam

Abstract

Since the unified theory of coherence and polarization for partially coherent vector beams was proposed by Gori and Wolf, the characterization, generation and propagation of partially coherent vector beams have been extensively studied. During the last decade, partially coherent vector beams with non-uniform polarization, also referred to as cylindrical vector partially coherent beams, have gained more and more attention. It was found that the intensity profile of focused azimuthally/radially polarized beam could be shaped by varying its initial spatial coherence. This characteristic may have potential applications in material thermal processing and particle trapping. Until now, there have been several reports concerning the generation of cylindrical vector partially coherent beams. However, in most of these reports a ground-glass diffuser was used, which generally restricts the generation of shell-model sources. In this paper, we theoretically and experimentally investigate the generation of radially polarized partially coherent beams with non-uniform correlation. According to the relation between phase correlation and optical coherence, we theoretically investigate the 2 × 2 cross-spectral density matrix and the coherence distribution of our generated non-uniformly correlated radially polarized partially coherent beams. In experiment, we generate dynamic random phase patterns with uniform distribution in time and inverse Gaussian distribution in space. A complete coherent radially polarized beam is divided into two parts by a polarizing beam splitter, i.e., the transmitted <i>x</i>-polarization component (HG₁₀ beam) and the reflected <i>y</i>-polarization component (HG₀₁ beam). The two orthogonally polarized components are respectively modulated with the two halves of a single phase-only liquid crystal spatial light modulator, thus generating a radially polarized partially coherent beam. We measure the correlation distribution of the generated beam in Young’s two-pinhole experiment. It is shown that the experimental observations are in agreement with our theoretical analyses. The generated partially coherent beam has an un-uniform correlation structure, and its coherence degree may be controlled by varying the Gaussian modulation half-width of the random phase. Our experimental results have also shown that the intensity profile of the radially polarized partially coherent beam can be modulated with the Gaussian modulation half-width. With the increase of Gaussian modulation half-widths and the gradual decrease of coherence degree, the intensity profile gradually transforms from a dark hollow beam profile into a flat-topped-like beam profile. The radially polarized partially coherent beams with non-uniform correlation may have some applications in optical manipulation and material thermal processing.