Research On Underwater Turbulence Detection Based On The Interference Characteristics Of Vortex Beam

With the exploitation of ocean resources and the clarity of marine national defense consciousness,the detection of moving targets in ocean and the wake tracking of ship targets have become an utterly important research topic.The detection and identification of underwater turbulence flow has gradually become a hot research topic in recent years.The natural distribution of temperature and salinity,and the dissipation of turbulent kinetic energy will form underwater turbulence with different intensity distribution,and underwater vehicles will form turbulence fields with different intensity distribution too.Therefore,the source of turbulence can be identified by detecting the intensity of underwater turbulence.On the basis of the displacement characteristics of the stripes caused by the interference between vortex beams and Gauss beams,a detection method for the intensity of underwater turbulence which based on the interference stripes migration is studied.The major tasks are as follows:1.The interference characteristics between vortex beam and plane wave and spherical wave are studied theoretically.The random phase function is obtained by using the Kolmogorov power spectrum.The transmission and interference characteristics of the Laguerre-Gaussian beam in turbulence are simulated using the random phase screen method.The effects of transmission distance and turbulence intensity on the intensity of vortex beam and the effect of turbulence intensity on the interference stripes are studied.The results show that when the turbulence intensity is constant,the spot size of the vortex beam is enlarged and the hollow becomes flat with the increase of the transmission distance.the intensity distribution will eventually evolve into the quasi Gaussian shaped distribution.When the transmission distance is constant,the spot size of the vortex beam has no obvious change,but the hollow becomes flat with the increase of the turbulence intensity.The larger the turbulence intensity is,the larger the displacement of the interference stripes caused by the vortex beam and the plane beam is.In the same turbulence intensity,the larger the topological charge,the smaller the displacement of the interference stripes position.2.The underwater turbulence intensity detection system based on the characteristics of vortex beam interference is established.On this basis,the displacement characteristics caused by the interference between vortex beams with different topological charges and Gauss beams in free space after turbulence are studied and analyzed experimentally.The interference stripes caused by the interference between the vortex beams of different intensity underwater turbulence and the Gauss beam in the air are measured and calculated.The displacements of interference stripes in different turbulence intensity are obtained.The experimental and theoretical results show that in the strong turbulent environment,the larger the topological charge,the better the transmission ability and the stability of the vortex beams propogating in the turbulence;In the same turbulence intensity,the larger the topological charge,the smaller the displacement of the interference stripes position,that is,the better the Anti-turbulence ability of the vortex beams;the displacement of interference stripes increases with the increase of turbulence intensity for vortex beams which have the same topological charge.The preliminary conclusions of theoretical and experimental studies show that using the detection method of underwater turbulence intensity based on the displacement of interference stripes,we can determine whether there is turbulence in water by the displacement of stripes generated by the interference between vortex beam and Gauss beam,and further estimate the underwater turbulence intensity by comparing with the known data.