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Highlights • Propagation model of radially polarized vortex beams in atmospheric turbulence is established. • A radially polarized vortex beam can reduce beam spreading and wander effects in the atmosphere. • Polarization modulation can be an approach to mitigate turbulent effects on OAM-based systems. Abstract Adopting a vortex beam with poor coherence can reduce turbulence-induced beam spreading and wander effects in the atmosphere, but it intensifies the degradation rate of its beam profile from a doughnut shape into a Gaussian shape. Transmission quality of Orbital–angular–momentum (OAM) mode carried by a vortex beam is closely related to its evolution of intensity distribution. After appropriate polarization modulation, a radially polarized vortex beam has a better performance on the reduction of beam spreading and wander effects than its scalar counterpart. A radially polarized vortex beam can also lower the degradation rate of its beam profile and keep "OAM information" a longer distance. Therefore, appropriate polarization modulation can be an effective approach to mitigate the adverse turbulent effects on OAM-based systems operated in the atmosphere. [ABSTRACT FROM AUTHOR]

Analytical expressions of average intensity and long-term beam width for a radially polarized multi-Gaussian Schell-model (MGSM) beam in anisotropic atmospheric turbulence are developed based on the extended Huygens-Fresnel principle. The influences of anisotropic non-Kolmogorov turbulence and source parameters on the average intensity, polarization and long-term beam spreading of radially polarized MGSM beam are examined in detail. The source correlations, free-space diffraction and turbulent effect jointly affect both the intensity and polarization profiles of the beam propagated in the atmosphere. As a radially polarized MGSM beam propagates in the atmosphere, increasing the associated beam order can lower the evolution rate from its flat-topped beam profile into a Gaussian beam profile because of the turbulent effect. Variations in the average intensity and long-term beam width are closely related to the propagation distance, power spectrum index, inner-scale, initial spatial coherence, and beam width. The atmospheric turbulence-induced beam spreading is generally suppressed with the enhanced anisotropy coefficient. [ABSTRACT FROM AUTHOR]

Based on the Lombardini et al. model that can predict the hydrodynamic damping of rough sea surfaces in the presence of monomolecular slicks and the “choppy wave” model (CWM) that can describe the nonlinear interactions between ocean waves, the modeling of time-varying nonlinear sea surfaces damped by natural or organic sea slicks is presented in this paper. The polarimetric scattering model of second-order small-slope approximation (SSA-II) with tapered wave incidence is utilized for evaluating co- and cross-polarized backscattered echoes from clean and contaminated CWM nonlinear sea surfaces. The influence of natural sea slicks on Doppler shift and spectral bandwidth of radar sea echoes is investigated in detail by comparing the polarimetric Doppler spectra of contaminated sea surfaces with those of clean sea surfaces. A narrowing of Doppler spectra in the presence of oil slicks is observed for both co- and cross-polarization, which is qualitatively consistent with wave-tank measurements. Simulation results also show that the Doppler shifts in slicks can increase or decrease, depending on incidence angles and polarizations. [ABSTRACT FROM AUTHOR]

• Beam shape coefficients of high-order vector Bessel-Gaussian beams are derived. • Incident beam and scatterer parameters can highly influence the scattering results. • It is not feasible to recognize the relative humidity of aerosol environment by using the differences of scattering intensities. Based on the generalized Lorenz-Mie theory (GLMT) and the angular spectrum decomposition method (ASDM), we derive the beam shape coefficients (BSCs) of high-order vector Bessel Gaussian beams (H-VBGB), and investigate the interaction mechanism of H-VBGB illuminating a spherical marine aerosol. Linear (x, y), circular (left, right), azimuthal and radial polarizations are considered. The effects of various parameters characterizing the incident beam and the aerosol on the normalized differential scattering cross section (DSCS) are investigated. Numerical results show that the normalized DSCS is very sensitive to fluctuations in the parameters, and that the distinctions of incident beams may highly influence results. The relative humidity of aerosol performs similar effects on results for all polarizations, so it is not feasible to recognize the relative humidity of aerosol environment by using the differences of normalized DSCS for various polarization states. We provide a reference for the practical use of the scattering features of non-diffractive beams illuminating spherical calibrators. [ABSTRACT FROM AUTHOR]

• A radiation model is proposed for the ultraviolet radiation properties of a gas-solid two-phase plume containing ablation particles. • The in-scattering source function of the aircraft plume is calculated statistically averaging the scattering properties of the particle swarm. • The effect of the phase change of the ablation particles on the radiation characteristics of the plume is considered. We propose a radiation model for a coupled gas-solid two-phase flow that includes ablation particles. This model is designed to compute the UV radiation characteristics of a plume containing ablation particles, employing the SHDOM method. The model considers the distribution characteristics of the ablation particles. Subsequently, we calculates the scattering phase function of these particles, along with a cumulative probability distribution, using the principles of Mie theory. The impact of ablation particle presence or absence on plume radiation characteristics is assessed, and the influence of ablation particle phase transition on plume radiation characteristics is also examined. The results suggest that adding ablation particles significantly boosts the UV radiation emitted by the plume, resulting in an average increase in radiance of approximately 65 % after the ablation process. In addition, the effects of changes in the phase state of the particles were studied in detail, with changes in particle phase increasing the average radiance within the plume by about 43 %. The results of this research have potential to advance aircraft stealth capabilities, characterize operating conditions of combustion chambers and aid in studying thermal protection materials. [ABSTRACT FROM AUTHOR]

When a hypersonic vehicle flies in near-space, the electron density of the plasma surrounding the aircraft is inhomogeneous and varies with time. Ablation occurs around the vehicle as the temperature rises. Therefore, investigating the propagation characteristics of electromagnetic (EM) waves in a space/time inhomogeneous and fully ionised dusty plasma sheath is important. In this article, a space/time inhomogeneous dusty plasma sheath model is first established. The expression of the dielectric coefficients of weakly collisional and fully ionised dusty plasma sheath is adopted. The shift-operator finite difference time-domain method is used to calculate the reflection and transmission coefficients of different dusty particle concentrations and radii, changes in electron density with time, electron temperatures and ion charges in the terahertz (THz) band. Finally, the propagation characteristics of THz waves with different electron density distributions at eight re-entry heights are analysed. Results show that increasing the incident wave frequency can effectively improve the effects of dusty particle concentration and radius, electron temperature and ion charge on the transmission of the EM wave. Different electron density change forms and electron density distributions significantly influence the propagation properties of THz waves. [ABSTRACT FROM AUTHOR]

• Single scattering model of single Mie scattering model of the raindrop particles under incident Bessel beams is established. • Energy attenuation characteristics of high-order Bessel beams transmission in rainfall atmospheric medium are simulated. • Penetration ability of high order Bessel vortex beam in rainfall environment is significantly stronger than that of non-vortex beam. Vortex beam propagates in the atmospheric environment, it interacts with the floating cloud, fog, rain and other micro particles, the absorption and scattering effects will lead to the energy attenuation of vortex beam, and result in the degradation of the transmission quality of vortex beam signal. Single scattering between Bessel vortex beam and raindrop particles is simulated based on generalized Lorentz Mie theory. Combined with the raindrop particle size distribution model, the transmission and attenuation characteristics of Bessel vortex beam in rainfall environment are analyzed. Bessel vortex beam with orbital angular momentum (OAM) has multiring intensity structure and spiral phase distribution, and the extinction efficiency factor of Bessel vortex beam caused by raindrop absorption and scattering in rainfall environment is smaller than that of Gaussian beam. Bessel vortex beam has the weaker energy attenuation in rainfall, and has stronger penetration ability of rain and fog. With the increase of topological charge, the extinction efficiency factor and energy attenuation rate caused by raindrop absorption and scattering further decrease. Bessel vortex laser with larger topological charge and bigger axial cone angle has stronger penetrating ability in rainfall environment. [ABSTRACT FROM AUTHOR]

We establish a model for lognormal distribution of monomer radius and number of alumina particle clusters in plume. According to the Multi-Sphere T Matrix (MSTM) theory , we provide a method for finding the statistical average of optical properties for alumina particle clusters in plume, analyze the effect of different distributions and different detection wavelengths on the statistical average of optical properties for alumina particle cluster, and compare the statistical average optical properties under the alumina particle cluster model established in this study and those under three simplified alumina particle models. The calculation results show that the monomer number of alumina particle cluster and its size distribution have a considerable effect on its statistical average optical properties. The statistical average of optical properties for alumina particle cluster at common detection wavelengths exhibit obvious differences, whose differences have a great effect on modeling IR and UV radiation properties of plume. Compared with the three simplified models, the alumina particle cluster model herein features both higher extinction and scattering efficiencies. Therefore, we may find that an accurate description of the scattering properties of alumina particles in aircraft plume is of great significance in the study of plume radiation properties. [ABSTRACT FROM AUTHOR]

In this paper, diffusion limited aggregation (DLA) algorithm is improved to generate the alumina particle cluster with different radius of monomers in the plume. Scattering properties of these alumina clusters are solved by the multiple sphere T matrix method (MSTM). The effect of the number and radius of monomers on the scattering properties of clusters of alumina particles is discussed. The scattering properties of two types of alumina particle clusters are compared, one has different radius of monomers that follows lognormal probability distribution, another has the same radius of monomers that equals the mean of lognormal probability distribution. The result show that the scattering phase functions and linear polarization degrees of these two types of alumina particle clusters are of great differences. For the alumina clusters with different radius of monomers, the forward scatterings are bigger and the linear polarization degree has multiple peaks. Moreover, the vary of their scattering properties do not have strong correlative with the change of number of monomers. For larger booster motors, 25–38% of the plume being condensed alumina. The alumina can scatter radiation from other sources present in the plume and effect on radiation transfer characteristics of plume. In addition, the shape, size distribution and refractive index of the particles in the plume are estimated by linear polarization degree. Therefore, accurate scattering properties calculation is very important to decrease the deviation in the related research. [ABSTRACT FROM AUTHOR]

We simulate the clusters of alumina particles using the parallel diffusion limited aggregation algorithm (DLA), and solve the scattering matrixes of the alumina particles in different phase states (alpha phase, gamma phase and liquid) through the multiple sphere T matrix method in UV. The effect of the number of monomers, fractal dimension and incident wavelength to the scattering phase function of the clusters of alumina particles is discussed. The results show that the different of the number of monomers, fractal dimensions and incident wavelengths have significant effect on the scattering properties of the clustered alumina particle. The researchers used to make the alumina particle equivalent to the alpha phase spherical particle, but it is too simplistic. We compare the scattering phase functions of the equivalent volume sphere (EVS), the equivalent surface sphere (ESS) and the clusters of alumina particles in three kinds of phase states. The results show that the backward scattering would be overestimated if the alumina particle is equivalent to the alpha phase spherical particle. Accurate phase function calculation in different phase states is very helpful to study the radiation propagation characteristics of aircraft plume. [ABSTRACT FROM AUTHOR]

Abstract: Debye series expansion (DSE) is employed to the analysis of radiation pressure force (RPF) exerted on biological cells induced by high-order Bessel beams (BB). The beam shape coefficients (BSCs) for high-order Bessel beams are calculated using analytical expressions obtained by the integral localized approximation (ILA). Different types of cells, including a real Chinese Hamster Ovary (CHO) cell and a lymphocyte which are respectively modeled by a coated and five-layered sphere, are considered. The RPF induced by high-order Bessel beams is compared with that by Gaussian beams and zeroth-order Bessel beams, and the effect of different scattering processes on RPF is studied. Numerical calculations show that high-order Bessel beams with zero central intensity can also transversely trap particle in the beam center, and some scattering processes can provide longitudinal pulling force. [Copyright &y& Elsevier]