Research On The Paraxiality Of Airy Beam And Its Propagation Characteristics In Atmospheric Turbulence

The problem of laser space transmission is a research field with practical and significant application.Especially in recent years,Airy beams have attracted great attention due to its excellent characteristics.The characteristics of the propagating paraxiality of the laser beams in space directly affect its light intensity variation and application.Atmospheric turbulence will reduce beams quality,undermine the stability of wireless optical communications,and improve bit error rate of channel.The atmospheric turbulence transmission characteristics of laser beams are important indicators for evaluating a space communication system.Therefore,it is of great practical significance to study the spatial paraxiality transmission and atmospheric turbulence transmission features of Airy-like beams.The fully and partially coherent Airy vortex beams are taken as the research object.Based on the source plane electric field of Airy vortex beams,the analytical expressions for the degree of paraxiality of fully coherent Airy vortex beams are obtained by using the angular spectrum theory and the definition of degree of paraxiality of monochromatic light.And the cross-spectral density,the Schell model and the definition of the degree of paraxiality of monochromatic light are used to calculate the analytical expression of the degree of paraxiality of partially coherent Airy vortex beams.The effects of optical parameters and optical vortex on paraxiality of Airy vortex beams are systematically analyzed.For coherent Airy vortex beams,the influence of coherent length on its degree of paraxiality is also emphasized.It is found that a larger truncation factor leads to a higher paraxiality.Further the effect of topological charge on the paraxiality gradually emerges as the truncation factor increases.For a partially coherent Airy vortex beam,the larger the beam width factor and the truncation factor,the larger the degree of paraxiality.In order to derive the theoretical analytical expression of the degree of polarization of the beam in turbulence.The cross-spectral density at the z-plane of the beams in atmospheric turbulence is obtained by utilizing the partially coherent Airy-Gaussian(AiG)beams source plane electric field and the extended Huygens-Fresnel principle,Rytov phase approximation and unified theory of polarization and coherence.Comparative analysis between horizontal and slant turbulent atmosphere of the effects of each light parameter on degree of polarization have been described.We find that the degree of polarization of the AiG beams will return to its initial value in the far-field turbulent transmission,and a longer transmission distance is required to return to the initial value in slant turbulence.In horizontal case,the fluctuation of the degree of polarization becomes smaller as the turbulence increases.Larger value of the zenith angle,the receiving height,the truncation factor and the distribution factor or a smaller coherence length is benefit to obtain a larger peak of degree of polarization of the AiG beams.Compared horizontal turbulent path,AiG beams have a greater peak polarization in slant path,and suddenly returns to the initial polarization value requiring a longer distance.Based on the cross-spectral density,the other turbulent features of AiG beams are also studied,such as the mean-squared beam width,the angular spread,the centroid position,the evolution of light intensity,the kurtosis parameter and the Strehl ratio.The simulation found that the more obvious the mean-squared beam width and centroid displacement of the AiG beams will be obtained in the case of a stronger turbulence.There is a critical truncation factor a_c.a better angular spread can be obtained with a shorter transmission distance with a?a_c.Oblique turbulence has less effect on light intensity than horizontal turbulence.As the transmission distance increases,the K-parameter of the AiG beams in atmospheric turbulence approaches K _x=3.The large turbulence intensity causes the Strehl ratio to decrease rapidly.Through the establishment of theoretical model and simulation analysis,it provides a theoretical basis for selecting some appropriate parameters for Airy-like beams to obtain better paraxiality characteristics and selecting suitable optical parameters to reduce the influence of atmospheric turbulence.