Dynamic double slits for topological charge determination

Abstract

In this study, we verified experimentally the mathematical expression we derive that generally characterizes the diffraction of a Laguerre-Gaussian beam by a double slit. We find that for a topological charge l, the interference fringes shift by l orders and that the direction of the shifting depends on the sign of l. The shifting effect can be used to determine the sign and the magnitude of the topological charge of a vortex beam, as long as, the distance between the slits is optimal. With a digital micromirror device (DMD) which acts as a dynamic slit, the optimal distance between the slits can be easily determined.