Rectangular Coherent Vortex Beams And Their Propagation Characteristics In Atmospheric Turbulence

Vortex beams exhibit superior physical properties over ordinary beams in practical applications because of their orbital angular momentum and spiral phase wave front.However,the presence of atmospheric turbulence can negatively affect the beam transmission performance and thus lead to a reduction in beam transmission quality.Obtaining a more turbulence-resistant beam and mitigating the adverse effects of turbulence on beam transmission have been the key concerns.Therefore,it is an important task to construct a new model of vortex beam and to study its transmission characteristics in atmospheric turbulence,which can provide theoretical basis and guidance for the practical application of beam transmission.The innovation of this thesis is to construct two vortex beam models with rectangular coherence distribution using a new coherence modeling method and to study their transport properties in Non-Kolmogorov atmospheric turbulence.The details of the work are as follows:1.A new method for modeling coherence functions is introduced,which provides a convenient way to construct a novel beam model with rectangular coherence by constructing the coherence function as two functions of separable form with arbitrary variable dependence.2.The cross-spectral density functions of the Sinc-correlated partially coherent vortex beam and the Rectangular-correlated partially coherent vortex beam are constructed separately by using our proposed new method of coherence modeling under the condition that the non-negativity qualification for constructing the real cross-spectral density function is satisfied,and the coherence distribution of both beams is visualized and analyzed,and it is found that the coherence of both beams has the characteristics of the rectangular distribution.3.According to the generalized Huygens-Fresnell principle,the expressions of these two vortex bema’s cross-spectral density functions transmitted in the atmospheric turbulent medium are obtained after mathematical deduction by combining the source field cross-spectral density functions of the beams.With the help of simulation software,the beam transmission process in free space and atmospheric turbulence is simulated,and the beam profile changes and spectral density distribution laws are observed.In addition,the degree of influence of turbulence on the beam profile and intensity under different values of turbulence parameters is investigated.The results show that whether the two beams can stably maintain the light-intensity dark hollow distribution in the transmission is related to the parity of order n in the expression of their cross-spectral density functions.At the same time,the beams exhibit self-focusing characteristics and rotation around the optical axis when transmitted in free space.Under the influence of atmospheric turbulence,the beam intensity gradually decreases and the beam profile gradually expands with the increase of turbulence intensity and transmission distance,while the distribution of the spectral density gradually evolves from a hollow distribution to a Gaussianlike distribution.