<p>On the basis of the extended Huygens–Fresnel principle and the spatial power spectrum of the refractive index fluctuations of ocean water, a propagation formula for on-axis average intensity of hollow Gaussian beams (HGBs) in oceanic turbulence is analytically obtained. Furthermore, the propagation properties of an HGB in oceanic turbulence are studied numerically in detail. The numerical results indicate that the initial beams with a higher beam order, longer blue–green wavelength, and larger waist width are helpful in mitigating the influence of turbulent ocean. Meanwhile, an HGB may propagate a much longer distance in weak oceanic turbulence by decreasing the dissipation rate of mean-square temperature and the ratio of temperature and salinity, as well as increasing the dissipation rate of turbulent kinetic energy per unit mass of fluid. The simulations also verify that HGBs have more resiliency to oceanic turbulence effects than ordinary Gaussian beams. Our research is expected to provide useful guidance for understanding the propagation characteristics of structured light beams in turbulent media.</p>
An arbitrary order Bessel beam with arbitrary incidence is generated numerically in finite-difference time-domain (FDTD) method using a total-field/scattered-field (TF/SF) approach. This is implemented by decomposition of Bessel beam into a series of plane waves, which are projected into the FDTD simulation domain. The off-axis incidence case is realized by tuning the arrival time when the elementary plane wave gets to the center area of simulation domain, and the oblique incidence case is implemented by rotating the plane waves through Euler angles. Numerical examples concerning backscattering radar cross-sections (RCS) are presented to demonstrate the validity, accuracy, and capability of the proposed method. The results in this paper provide an efficient way to investigate the interactions of Bessel beams and particles with complex shape and composition using FDTD.
The analytical expressions of mode probability density (MPD) and crosstalk probability density (CPD) for LaguerreGaussian correlated Schell-mode (LGCSM) beams propagating through oceanic turbulence are established based on the geometrical optics approximation. Using the derived formulae and numerical simulation, the propagation characteristics of a single LGCSM beam in turbulent ocean are quantificationally analyzed in detail. The numerical results for the effects of all kinds of parameters on the MPD and CPD curves of a LGCSM beam propagating in the ocean environment are presented and illustrated. This research is expected to provide a convenient way and useful guidance to describe and treat the propagation of laser beam in turbulent medium.
With the fast development of sea surface target detection by optoelectronic sensors, machine learning has been adopted to improve the detection performance. Many features can be learned from training images by machines automatically. However, field images of sea surface target are not sufficient as training data. 3D scene simulation is a promising method to address this problem. For ocean scene simulation, sea surface height field generation is the key point to achieve high fidelity. In this paper, two spectra-based height field generation methods are evaluated. Comparison between the linear superposition and linear filter method is made quantitatively with a statistical model. 3D ocean scene simulating results show the different features between the methods, which can give reference for synthesizing sea surface target images with different ocean conditions.
By using Intel Visual Fortran and Visual Studio 2013, a software for calculating radar cross section of the metal and
the plasma three-dimensional composite target are given, based on the method of MOM and FDTD. This software can
calculate radar cross section of the near space aircraft covered the plasma sheath, and this work has an important
strategic significance in the future.
In this paper, an analysis of scattering properties of aggregated particles illuminated by an arbitrary shaped beam is implemented using GLMT. A theoretical treatment for an aggregate of particles illuminated by an arbitrarily incident beam is briefly presented, with special attention paid to the calculation of beam shape coefficients of a shaped beam. The theoretical treatment and the home-made codes are verified by making a comparison between our numerical results and those obtained using a public available T-Matrix code MSTM. Good agreements are achieved which partially indicate the correctness of both codes. Furthermore, some new numerical results concerning the scattered fields of aggregated particles illuminated by a focused Gaussian beam are presented.
The properties of Morphological Dependant Resonance (MDR)'s for spherical, cylindrical microcavity have been investigated. The behaviour of locations, quality factors of resonances for spherical and cylindrical microcavity has been discussed. The resonance spectrum for symmetric microcavity is rigorously calculated and shows the strong dependence of the resonance spectrum on the physical characteristics of the microcavity. Note that the position of the resonance peaks is extremely sensitive to wavelength or diameter, permitting a very accurate determination of symmetric microcavity size.