A.V. Averchenko – Post-graduate Student, Faculty of Physics, Department of Optics, Spectroscopy and Nanosystems Physics, Lomonosov Moscow State University
A.M. Zotov – Ph. D. (Phys.-Math.), Senior Research Scientist, Faculty of Physics, Department of Optics, Spectroscopy and Nanosystems Physics, Lomonosov Moscow State University
P.V. Korolenko – Dr. Sc. (Phys.-Math.), Professor, Faculty of Physics, Department of Optics, Spectroscopy and Nanosystems Physics, Lomonosov Moscow State University
During development and optimization different communication systems, adaptive and metrological devices a problem of receiving specific data about amplitude and phase structure of electromagnetic waves often appears. Phase fluctuations of radiation due to spatial and temporal changes of the structure of a wavefront turn out in the spotlight. For their registration a variety of wavefront sensors are used. In this article we consider getting information about wavefront of electromagnetic bunches using shear interferometer and in the presence of a noise component. The aim of this work is to develop and to test universal methods of processing shear interferograms, which can be applied to both cases of weak and strong fluctuations, characterized by the presence in the wave front of helical dislocations. Proposed algorithm of restoring of wavefront based on an analysis behavior zero-value lines of complex-amplitude in conditions of level variety of phase fluctuations. As test beams we used simple fields contain one dislocation on beam axis and the speckle fields, generated by adding the plane waves with random phases and random propagation directions. On the borders of the speckles in the points with zero intensity helical dislocations of the wave front are formed. The position of the dislocations can be identified by the intersection of zero lines for the real and imaginary parts of the amplitude. The presence of dislocations causes branching of the fringes in the area of their location at the shear interferogramm. The result of restoration of the intensity and phase in a satisfactory manner corresponds to the original beam structure and it shows prospects of application the developed algorithm in practical researches. The process of getting interferometric data of radiation diffraction propagation in cases of primary phase fluctuation was modeled. A modeling showed that the critical level of primary phase fluctuations exists and its excess in the area, where the wave parameter D > 1, with a high degree of probability leads to forming of helical dislocations. The critical level of fluctuations is characterized by the standard deviation of the phase from the phase distribution of plane wave, equal σφ = π/4.
Thus, a study performed indicates the possibility of using the interferometric information to describe an important class of phenomena associated with different types of radiation wavefront conversion, including cases of change of its topology.
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