Detecting optical vortices in 2D

Abstract

Higher-order optical vortices are inherently unstable in the sense that they tend to separate in a series of vortices with a unity charge. In this study, we demonstrate a technique to detect an optical vortex using its far-field diffraction by a triangular aperture. By raster scanning a triangular aperture in two dimensions across a beam containing a single vortex, we record the resulting structured diffraction pattern. Then, we measure the intensity signal at the pattern's center. We do this by introducing a pinhole whose size S can be controlled. By plotting the intensity values transmitted through the pinhole for different scanning points, we find that the lowest intensity region in the map locates a vortex. We show through another experiment that our technique is able to resolve vortex pairs that are 86.4 μm apart. Our results can be significant in understanding multiple-vortex interactions in other optical beams, such as in x-ray and electron beams.