Arbitrary light beams and propagation characteristics in atmosphere

In this study, the effects of atmospheric turbulence on flat topped(FT), general-type and arbitrary source beams in horizontal optical links are investigated. Primarily, the source and receiver plane characteristics of FT beam traveling in turbulent atmosphere are examined. To this end, source size, beam power and M2 factor of source plane FT beam are derived. For a turbulent propagation medium, via extended Huygens Fresnel diffraction integral, the receiver plane intensity is found. Power captured within an area on the receiver plane is calculated. Kurtosis parameter and beam size variation along the propagation axis are formulated. When propagating in turbulence, the FT beam first will form a circular ring in the center. As the propagation length increases, the circumference of this ring will become narrower, giving rise to a downward peak emerging from the center of the beam, eventually turning the intensity profile into a pure Gausssian shape. Subsequently, a simulator is designed in MATLAB code which gives the propagation characteristics of a general-type beam in turbulent atmosphere. When the required source and medium parameters are entered, the simulator yields the average intensity profile along the propagation axis in a video format. Some samples of the simulator output are presented. Eventually, The propagation of arbitrary laser beams in either free space or turbulent atmosphere is examined. Arbitrary source field profile is produced by decomposing the source into pixels. The received field through the propagation in either free space or turbulent atmosphere is found by superposing the contributions from all source pixels via extended Huygens Fresnel integral. This method enables us to evaluate the received intensity originating from any type of source field. Using the arbitrary beam excitation, intensity and on-axis scintillation index of various laser beams such as cos-Gausssian, higher order annular and general type beams are checked to be consistent with the already existing results in literature, and the received intensity distributions and irradiance fluctuations are obtained for some original arbitrary beam field profiles. In weak atmospheric turbulence condition by use of Rytov method solution, the scintillation index is calculated by using numerical integration. Under the chosen source and propagation parameters, it is found that for all beam types, as the propagation length increases the scintillation index increases. For discretionary beams, scintillation index fluctuating in Fresnel region, grow up in far field region. The results obtained in this work would be useful in atmospheric optical links to find out the optimum beam profile that will minimize the scintillation index.