Far-field slit diffraction and express diagnostics of optical vortices

Abstract

The slit diffraction of circular OV beams is studied both theoretically and by experiment, with explicit involvement of the incident beam convergence or divergence (finite value of the wavefront curvature radius). Based on the example of Laguerre-Gaussian mode with zero radial index and non-zero azimuthal index m we confirm that the far-field diffraction pattern contains exactly |m| bright lobes elongated orthogonally to the slit (which was reported previously) and show that the far-field profile possesses an asymmetry with respect to the slit axis depending on the wavefront curvature (which is a new result). Being combined, these features enable simple and efficient means for the simultaneous express diagnostics of the magnitude and the sign of the OV topological charge, which can be useful in many OV applications, including the OV-assisted metrology and information processing.