Vortex Beams In Turbulent Atmosphere Research Articles

Propagation properties of partially coherent radially polarized rotationally-symmetric power-exponent-phase vortex beams in turbulent atmosphere

In this paper, the propagation properties of partially coherent radially polarized rotationally-symmetric power-exponent-phase vortex beams (RP-RSPEPVBs) in turbulent atmosphere were investigated. Based on the extended Huygens-Fresnel principle and unified theory of coherence and polarization, the theoretical propagation model was established. Then, the numerical simulations were carried out to reveal the evolution of intensity distribution, spectral degree of coherence (DOC) and spectral degree of polarization (DOP) in turbulent atmosphere. The results showed that although the partially coherent RP-RSPEPVBs diverged during the propagation, the spatial structure remains analogous, and the relatively larger waist widths gain smaller divergence. Moreover, the optical pattern can be evidently modulated by optical parameters, as the number of sidelobes can be changed with topological charge l, and the continuity of the light spot as well as the rotating speed around the optical axis can be influenced by power exponent n. Besides, the spectral DOC and DOP would decrease with larger propagation distance and refractive-index structure constant, but decrease less with a shorter coherence width. This work may be helpful in fields such as remote sensing and optical communication.

Propagation properties of partially coherent radially and azimuthally polarized vortex beams in turbulent atmosphere

Analytical formulas for the average intensity of the partially coherent radially and azimuthally polarized vortex (PCRPV and PCAPV) beams propagating through the turbulent atmosphere are derived based on the extended Huygens-Fresnel principle. The effect of the different topological charge number m of PCRPV beam and PCAPV beam in turbulence on average intensity and degree of hollowness (DOH) has been studied in detail. It can be found that PCRPV beam and PCAPV beam in turbulence with the larger topological charge m can greatly keep dark hollow constructure on propagation. And we have studied the orientation angles of the polarization ellipse of the PCRPV and PCAPV beams with different m in atmospheric turbulence. The results show that the capacity to keep radial polarization decline with the increase of topological charge m. In addition, we combined the complex screen method and multi-phase screens method to simulate the propagation of PCRPV beam and PCAPV beam in atmospheric turbulence for verifying our theoretical results. It is shown that the simulated results are consistent with theoretical results. Our study could be important for free-space optical communications.

Scattering of partially coherent vortex beam by rough surface in atmospheric turbulence.

A double-passage propagation model of partially coherent Laguerre-Gaussian (LG) vortex beams with orbital angular momentum (OAM) modes in turbulent atmosphere after scattering from Gaussian rough surfaces was formulated. Rough surface scattering had a weak effect on the spreading of a vortex beam in turbulent atmosphere. However, it severely influenced the phase on this beam, rapidly reducing the original OAM mode's relative intensity. The OAM spectrum information is more useful than the intensity information for rough surface object remote sensing. Additionally, by comparing the scattering intensity in monostatic and bistatic systems, the enhanced backscatter of vortex beams from Gaussian rough surfaces was verified.

Compensation for the orbital angular momentum of a vortex beam in turbulent atmosphere by adaptive optics

A method which can be used to compensate for a distorted orbital angular momentum and wavefront of a beam in atmospheric turbulence, simultaneously, has been proposed. To confirm the validity of the method, an experimental setup for up-link propagation of a vortex beam in a turbulent atmosphere has been simulated. Simulation results show that both of the distorted orbital angular momentum and the distorted wavefront of a beam due to turbulence can be compensated by an adaptive optics system with the help of a cooperative beacon at satellite. However, when the number of the lenslet of wavefront sensor (WFS) and the actuators of the deform mirror (DM) is small, satisfactory results cannot be obtained.

Propagation properties of partially coherent four-petal Gaussian vortex beams in turbulent atmosphere

The partially coherent four-petal Gaussian vortex beam is introduced and described by analytical expressions. The analytical propagation equation for partially coherent four-petal Gaussian vortex beam in turbulent atmosphere is derived by using the extended Huygens–Fresnel diffraction integral formula. The influences of refraction index structure, beam order n, topological charge M and the coherence length on the average intensity distributions of beam are investigated by numerical examples.

Intensity and polarization properties of elliptically polarized vortex beams in turbulent atmosphere

Abstract Based on the extended Huygens–Fresnel principle, the propagation of elliptically polarized vortex beams in a turbulent atmosphere is investigated. The analytical expressions for the average intensity and degree of polarization of the elliptically polarized vortex beams are derived in a turbulent atmosphere, respectively. The influences of polarization ellipticity, topological charge, beam width, and structure constant of the atmospheric turbulence on average intensity and degree of polarization are numerically demonstrated and analyzed in detail.

Spectral properties of a random electromagnetic partially coherent flat-topped vortex beam in turbulent atmosphere

Based on the extended Huygens–Fresnel principle, we introduced the analytic expression of a random electromagnetic partially coherent flat-topped (PCFT) vortex beam propagating in Kolmogorov atmospheric turbulence. The spectral properties of the random electromagnetic PCFT vortex beam are explored by using the unified theory of coherence and polarization. It is demonstrated by numerical results and found that after propagating through turbulent atmosphere, the spectral density, the spectral degree of polarization as well as the spectral degree of coherence of the random electromagnetic PCFT vortex beam vary. The variations of the spectral properties depend closely on the strength of atmospheric turbulence and the properties of the source beam, i.e. the topological charges, the order of flatness, the waist width as well as the initial spatial coherence. In addition, the distributions of the spectral density and the spectral degree of polarization undergo several stages of evolution and finally tend to Gaussian profile at the receiver plane. Some possible explanations have also been given for these interesting physical phenomena.

Spectral changes of polychromatic stochastic electromagnetic vortex beams propagating through turbulent atmosphere

The unified theory of coherence and polarization and the propagation law of 2 × 2 cross-spectral density are employed to investigate spectral changes of the polychromatic stochastic electromagnetic vortex beam propagating in turbulent atmosphere. It is shown that the spectral changes of a polychromatic stochastic electromagnetic vortex beam in turbulent atmosphere differ from those of the beam without vortex. Specially, the on-axis relative spectral shifts exhibit not only blue-shift, but also red-shift. It is also shown that the topological charge, the correlation length and the refractive index structure constant influence the spectral changes of polychromatic stochastic electromagnetic vortex beams in a turbulent atmosphere.