When a light beam passes through a strongly atmospheric turbulence, phase singularities appear in some points of the wave front surface. For reconstruction of these beams or extracting topological charge of a pure Laguerre-Gaussian beam, it is needed to determine the center of the vorticities. In this work, we introduce a new method for this purpose by use of the wavefront slope value data. For a case, center of vortex beam and the selected origin for the coordinate system match together, the variance of determined topological charge to be minimized. Wavefront slops can be extracted with a wavefront sensor like a two-channel moiré based wavefront sensor. In experiment, lens phase function or a white noise are added to an azimuthally dependence phase of an incident beam. This is done by use of diffraction of a plane wave from a LCD, which is used as a spatial phase modulator. In addition, we used amplitude forked grating and allow passing diffracted beam through a turbulent medium. Then, we determined centers of these beams and noted some considerations for this process.

Keywords: Laguerre-Gaussian Beam, Moiré Deflectometry, SLM, Topological Charge, Vortex Beam

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