Propagation Characteristics And Light Field Regulation Of Partially Coherent Vortex Beams In The Atmosphere

The application of vortex beams in remote sensing detection will inevitably be affected by the atmosphere.When the vortex beams is transmitted in the atmosphere,the turbulent atmosphere will lead to the degradation of the coherence of the vortex beam,the dispersion of the orbital angular momentum spectrum,and the redistribution of the beam energy on the beam cross section,thus affecting the sensitivity of the vortex beam to detect the angular velocity of rotating objects.Partially coherent beams are less affected by turbulence than fully coherent beams,while partially coherent vortex beams combine the excellent characteristics of partially coherent beams and vortex beams.Therefore,it is of great significance to study the propagation characteristics of partially coherent vortex beams in turbulent atmosphere.In this paper,the orbital angular momentum characteristics,coherence and intensity distribution of partially coherent vortex beams in turbulent atmosphere are studied.The main work is as follows:1.The intensity distribution and phase structure of vortex beams in free space are studied.According to the theory of orbital angular momentum spectrum of fully coherent beams,the orbital angular momentum characteristics of Laguerre-Gaussian(LG)beams propagating in free space are studied.The theory of partially coherent beams,the scalar diffraction theory and the turbulent atmosphere theory are analyzed.2.The coherence of vortex beams is reduced by using random rough surface.The intensity distribution of partially coherent vortex beams is studied.The random rough surface is simulated.The intensity distribution of LG beam passing through random rough surface is calculated.The intensity distribution of LG beam passing through ground glass is studied by experiment.The expression of intensity distribution of partially coherent LG beams propagating in free space and turbulent atmosphere is derived.The intensity distribution of partially coherent vortex beams with different initial coherent length in free space is studied.The intensity distribution characteristics of partially coherent LG beams propagating in turbulent atmosphere are analyzed.The results show that when the initial coherent length of the partially coherent LG beam is close to the spot size,the intensity distribution of the beam propagating a certain distance in the free space is gradually transformed into a hollow distribution;The phase singularities of partially coherent LG beams disappear after transmitting a certain distance in turbulent atmosphere.3.Based on the generalized Huygens-Fresnel principle and the cross spectral density function of LG beams at the source plane of the optical field,the cross spectral density function of partially coherent LG beams in the turbulent atmosphere is derived.According to the theory of partially coherent beams and the theory of orbital angular momentum spectrum of fullycoherent beams,the integral expression of orbital angular momentum spectrum of partially coherent vortex beams in turbulent atmosphere is derived.The orbital angular momentum characteristics and coherence of partially coherent LG beams in horizontal path propagation of turbulent atmosphere are studied.The orbital angular momentum characteristics and coherence of partially coherent LG beams in oblique path propagation of turbulent atmosphere are analyzed.The results show that when the initial coherent length of partially coherent LG beams is the same as the beam waist radius,the relative power of the initial orbital angular momentum state decreases with the increase of beams width at a certain distance of horizontal propagation in turbulent atmosphere;in the process of oblique propagation in turbulent atmosphere,the transverse coherent length of the beam increases rapidly with the increase of the distance,and when the propagation distance reaches at a certain value,the transverse coherent length of the beam tends to be stable.The results of this paper are valuable for the application of vortex beams in the field of optical remote sensing.