Vasnetsov M. Optical beams with wave fronts dislocations

The research is devoted to a systematic study of main properties of optical beams with phase singularities, or wav-front dislocations. The origin of appearance of orbital angular momentum (OAM) is explained for a beam with an optical vortex. Edge dislocations of wave fronts are considered on a model o interference of two two-dimensional or ordinary Gaussian beams. Scenarios of a collapse of a system of two transversal optical vortices and two lines of phase saddles are shown, as well as an unfolding of an edge dislocation in the collision with the saddle line. On the basis of a holographic principle, a method of generation of laboratory beams with wave-front dislocations in the form of axial and off-axis optical vortices was developed, particularly as a superposition of two Laguerre-Gaussian modes. A term "combined beams" is introduced, as a superposition of two or more Laguerre-Gaussian modes. Trajectories of optical vortices are considered for combined beams. A possibility is demonstrated for a vortex trajectory to leave the beam, and therefore a violation of the low of the topological charge conservation. For a combined beam an analysis of OAM distribution across the beam was performed, and a general formula of OAM interference was obtained. With the aid of laboratory beams first time in the optical experiment an annihilation of optical vortices with opposite signs of topological charges and rotation of a pair of vortices with topological charges of equal sign around optical axis were studied. A scheme of spatial separation of components of an optical beam, which are different in the sense of orbital angular momentum value was proposed and experimentally realized. Experiments were performed for the study of phase dislocations formation in a beam due to light-induced lens in a nonlinear optical medium. In the first time a doubling of the topological charge of an optical vortex in the process of second-harmonic generation was shown. In the first time in an optical region a direct experiment was carried out for observation of the rotational Doppler effect for beams with orbital angular momentum, on the level of frequency shift 1 Hz. One-beam interferometer was realized for the measuring of phase shift between components with zero and nonzero OAM while rotation of a combined beam. In the first time a spectral selection of OAM components was obtained for a rotating beam.