Research On Echo Characteristics Of Rough Target Of Partially Coherent Vortex Beam In Atmospheric Turbulence

The vortex beam carrying orbital angular momentum has been a hot issue in modern study because it is a unique laser beam that is widely employed in optical communication,OAM multiplexing,quantum information,and other domains.Light intensity scintillation,beam expansion,and other phenomena brought on by air turbulence effects can all be successfully suppressed by partially coherent beams.A unique type of vortex beam that combines the benefits of partially coherent beams and vortex beams is known as a partially coherent vortex beam,it has very important research value.In this paper,two methods are used to study the echo characteristics of beams passing through rough target surface in atmospheric turbulence environment.The contents are as follows.(1)The random phase screen and random Gaussian rough target model are established,and the echo characteristics of vortex beam passing through rough target under atmospheric turbulence are studied by numerical simulation method.The influence of different parameters on the intensity speckle is analyzed.The results show that with the increase of topological charge and beam waist radius,the number of speckle particles increases and the size decreases gradually.Compared with weak turbulence,the number and size of speckles change significantly under strong turbulence.With the decrease of the inner scale,the speckle particles gradually become smaller,while the change of the outer scale speckle has no obvious change;the speckle size increases with the increase of the coherence length of the rough surface.With the increase of the root mean square of the rough surface,the speckle size and number do not change.(2)An analytical method based on the generalized Huygens-Fresnel principle is used to compute the cross-spectral density function and the average intensity expression of the partially coherent vortex beam propagating on the rough target surface in the air turbulence environment.Based on the one-way transmission model,combined with the Gaussian rough surface model,the two-way echo link model of the partially coherent vortex beam propagating on the rough target surface in the atmospheric turbulence is established.Analytical approach is used to determine the cross-spectral density function and average intensity expression of the echo light field when the beam reaches the receiving end after passing through the rough target.(3)Based on the analytical method,the statistical characteristics of the beam echo are studied theoretically.According to the simulation,the effects of different light sources,turbulence and rough surface parameters on the second moment of the statistical characteristics of the echo:the intensity autocorrelation function and the beam propagation are analyzed.The results show that with the increase of topological charge,beam waist radius and coherence length,the intensity autocorrelation function decreases steeply and the beam expansion is more serious.At the same propagation distance,with the increase of turbulence intensity and the decrease of inner scale,the autocorrelation function of light intensity becomes smaller and smaller,the relative beam width increases gradually,and the beam propagation becomes more serious.When the inner scale remains unchanged and the outer scale changes,the autocorrelation function and the relative beam width do not change significantly.As the coherence length of the rough surface decreases,the half-peak value of the autocorrelation function decreases,and the beam expansion is more serious.As the root mean square of the rough surface increases,the intensity autocorrelation function and beam expansion do not change.For the use of partly coherent vortex beams in optical remote sensing,detection,and other relevant domains,the findings of this study are of major research significance.