Superposition theory of the spiral harmonics is employed to numerical study the transmission property of the orbital angular momentum (OAM) mode of Gaussian beam induced by atmospheric turbulence. Results show that Gauss beam does not carry OAM at the source, but various OAM modes appear after affected by atmospheric turbulence. With the increase of atmospheric turbulence strength, the smaller order OAM modes appear firstly, followed by larger order OAM modes. The beam spreading of Gauss beams in the atmosphere enhance with the increasing topological charge of the OAM modes caused by atmospheric turbulence. The mode probability density of the OAM generated by atmospheric turbulence decreases, and peak position gradually deviate from the Gauss beam spot center with the increase of the topological charge. Our results may be useful for improving the performance of long distance laser digital spiral imaging system.
Based on the scattering effect of optical vortex, the remote sensing for aerosol particles in marine atmosphere is investigated. The influences of orbital angular momentum (OAM) mode and beam width of Laguerre-Gaussian (LG) beam on the performance on the remote sensing for aerosol particles in marine atmosphere are analyzed numerically. The scattering properties of aerosol particles by LG beam are more sensitive to the change of relative humidity, compared to that of plane wave and Gaussian beam (GB). Remote sensing systems based on LG beam with OAM modes show superiority over traditional plane wave and Gaussian beam cases in detecting the changes in relative humidity of marine atmosphere aerosol. Results also indicate that, when the number of OAM modes p (l) increase, the Radar CrossSection (RCS) of aerosol particles alternating appear extreme values in the forward and backward scattering, because of the special ring-shaped distribution of LG beam. The forward and backward scattering of aerosol particles decrease with the increase in beam waist. As beam waist is less than the radius of aerosol particle, there exists a minimum value in the forward direction.
Analytical expression of the cross-spectral density matrix of the focused electromagnetic MGSM beams propagation through in non-Kolmogorov anisotropic turbulent atmosphere is obtained. With the help of this formulation, the influences of non-Kolmogorov anisotropic turbulence on the spectral density and the degree of coherence of such beams with turbulence inner scale and outer scale effects considered are discussed. The flat-topped intensity profile of the focused electromagnetic MGSM beams can be prolonged a long distance by suitable choices of the source parameters. Compared with the isotropic non-Kolmogorov atmospheric turbulence, anisotropic non-Kolmogorov turbulence with greater anisotropy coefficient produces less effect on the focused electromagnetic MGSM beams. The degree of coherence increased steeply in the initial increasing phase of propagation distance, it then turned round into the decline regimes after reaching a maximum value and trends to 0 after sufficiently long propagation distance. And the values of anisotropy coefficient, non-Kolmogorov power spectrum index, and turbulence inner scale have significant effects on the propagation distance. Increasing wavelength is a good alternative to improve the performance the focused electromagnetic MGSM beams in non-Kolmogorov anisotropic turbulent atmosphere.