Differentiating the phase structures of doughnut-like beams with similar intensity envelopes

摘要

We represent the straightforward techniques for differentiation of the phase structures of light beams of various origin but having similar intensity envelopes using doughnut-like beams as an example. Namely, we compare the phase structure of the set of beams: (ⅰ) a ring beam with smooth (vortexless) wavefront but with artificially introduced central amplitude zero, with Gaussian radial intensity distribution; (ⅱ) Laguerre-Gaussian mode LG_0~(±1) with the central vortex; (ⅲ) combined beam assembled from uncorrelated weighed Laguerre-Gaussian modes LG_0~1 and LG_1~1 with the central screw dislocation and with the ring edge dislocation of the spatial coherence function; (ⅳ) combined beam assembled from uncorrelated Hermite-Gaussian modes HG_0~- and HG_1~0 ; (ⅴ) combined beam assembled from correlated but orthogonal in polarization Hermite-Gaussian modes HG_0~1 and HG_1~0; (ⅵ) combined beam assembled from uncorrelated and orthogonal in polarization Hermite-Gaussian modes HG_0~1 and HG_1~0 . Experimental analysis and comparison of the phase structures (ⅰ) and (ⅱ) can be performed using a common interference technique with off-axis reference wave. Other mentioned cases cannot be analyzed by applying this technique. To differentiate the corresponding phase structures and associated singularities, we attract the united technique based on edge diffraction and use of an opaque strip screen placed at the analyzed beam. In cases (ⅴ) and (ⅵ). this technique is added by 2D Stokes polarimetry. The proposed techniques provide reliable diagnostics of common optical vortices, vortices of the spatial correlation functions, polarization singularities of completely (but inhomegeneously) polarized light beams, and the singularities of the complex degree of polarization from typical bending or a half-period shift of the Young's interference fringes at the shadow of the strip screen.