Transmission Characteristics Of Terahertz Bessel Vortex Beam In Magnetized Plasma

The terahertz Bessel vortex beam has many excellent properties.It combines the wide spectral bandwidth of terahertz radiation,good penetration,and the diffraction-free characteristics,self-healing properties,and the ability to carry orbital angular momentum.It has been widely used in optical tweezers,imaging,quantum entanglement and communication.However,in practical applications such as communication and imaging,the influence of environment on beam propagation characteristics must be considered.In this paper,the reflected and transmitted fields of Bessel vortex beam in single/multilayer magnetized plasma media are derived based on the cylindrical vector wave function expansion of Bessel vortex beam and the boundary conditions.For different polarization modes of incident beam,the effects of different parameters on the field intensity of reflected and transmitted beam and the distribution of orbital angular momentum are numerically simulated and analyzed.Finally,based on the propagation theory of vortex beam in random medium,the transmission characteristics of terahertz Bessel vortex beam in turbulent plasma are discussed by using multiple phase screen method.The main contents of this thesis are as follows:1.This paper introduced the basic properties and parameters of the plasma,as well as the scattering matrix method for calculating the reflection,transmission and absorption of electromagnetic waves by inhomogeneous plasma.Then the reflection,transmission and absorption characteristics of the left circular polarization and the right circular polarization wave in the magnetized plasma are analyzed by using the scattering matrix method.Finally,the properties and scalar representation of Bessel vortex beam and its cylindrical vector wave function expansion are introduced,and the field strength,phase and OAM states of the beam under different polarization modes are given.2.Based on the cylindrical vector wave function expansion of Bessel vortex beam,the internal field of Bessel vortex beam in magnetized plasma medium is derived.According to the boundary conditions,the reflection and transmission fields of Bessel vortex beam in single layer magnetized plasma medium are derived.Through comparing the transmission electric field trajectory and the reflection and transmission coefficients of LCP and RCP waves in the Faraday rotation effect calculated by this method and the analytical method,it is shown that the two groups of results are in good agreement and the correctness of this method is verified.The variation of reflection and transmission field profile and OAM states of the x polarized terahertz Bessel vortex beam in a single-layer magnetized plasma is numerically simulated.The results show that the thicker the plasma thickness,the greater the electron density and the greater the incident angle,the more serious the distortion and intensity attenuation of the transmitted field profile.As the external magnetic field increases,the proportion of the y component of the transmission electric field increases.Topological charge number has no effect on the OAM state distribution of reflection and transmission field.As the half-cone angle increases,the proportion of OAM modes in the reflection and transmission fields decreases.The larger the incident frequency,the greater the beam transmittance.3.Considering that the electron density distribution in the plasma is often uneven in the actual environment,the cascade expression of reflected and transmitted field expansion coefficient of Bessel vortex beam in layered magnetized plasma medium is derived.The reflection and transmission coefficients of the LCP and RCP waves calculated by this method and the SMM method are compared,which shows that the results of the two methods are in good agreement,and the correctness of the method is verified.The transmission characteristics of different polarized Bessel vortex beams in multilayer magnetized plasma are simulated numerically.The results show that by increasing the magnetic induction intensity,the transmittance of the right-handed polarization beam can be increased.And with the increase of magnetic induction intensity,the polarization mode of transmission field gradually becomes circular polarization after x polarization and radial polarization wave pass through magnetized plasma.Finally,the propagation of coaxial Bessel vortex beam with topological charge numbers 2 and-2 in magnetized plasma is simulated.The results show that as the magnetic induction intensity increases,the transmittance of the right-handed circularly polarized beam in the magnetized plasma increases and no mode crosstalk occurs.4.Based on the multiple phase screen method and fractal phase screen model,the transmission characteristics of terahertz Bessel vortex beam in turbulent plasma are numerically simulated.The results show that the anti-interference ability of Bessel vortex beam in plasma turbulence can be improved by increasing the topological charge number.