No abstract

Edge diffraction of a circular Laguerre-Gaussian beam represents an example of the optical vortex symmetry breakdown in which the hidden "vortex" energy circulation is partially transformed into the visible "asymmetry" form. The diffracted beam evolution is studied in terms of the irradiance moments and the moment-based parameters. In spite of the limited applicability of the moment-based formalism, we show that the "vortex" and "asymmetry" parts of the orbital angular momentum can still be reasonably defined for the hard-edge diffracted beams and retain their physical role of quantifying the corresponding forms of the transverse energy circulation.

No abstract

We present the results of the numerical investigation of the transverse profile evolution for a beam obtained by the edge diffraction of a circular Laguerre-Gaussian mode. It is shown that the energy penetrates into the geometric shadow region asymmetrically, which testifies for the transverse energy circulation in the incident beam. The intensity profile shows the "overall" rotation in agreement with the energy circulation handedness. The phase profile of the diffracted beam is characterized by the system of singularities (optical vortices) that migrate over the beam cross section and participate in topological reactions of emergence and/or annihilation. In the far field, the beam profile structure is simplified and becomes symmetric with respect to the axis orthogonal to the screen edge. No matter which part of the Laguerre-Gaussian beam is stopped by the screen, the far-field profile contains the optical vortex of the same sense as the incident one.

Abstract.A slit diffraction is widely used for express diagnostics of optical vortices (OVs). We propose a version of this method that employs relatively wide slits of the sizes comparable with the thickness of bright ring characterizing the OV-beam under test. Under such conditions the diffracted beam contains two bright lobes that propagate along the directions determined by local normals to the incident-beam wavefront in the slit plane. As a result, observations of the lobes' displacements within the beam cross section provide information on the local wavefront slope and, consequently, on the OV sign and topological charge. The evolution of the lobes' positions during the diffracted beam propagation visualizes a hidden energy circulation in the incident OV-beam and provides a direct and spectacular illustration of the internal energy flows.