Propagation Characteristics Of Gaussian Beam Research Articles

Influence of Outer Scale of Ocean Turbulence on Propagation Characteristics of Gaussian Beams

Influence of Outer Scale of Ocean Turbulence on Propagation Characteristics of Gaussian Beams

Analysis of Gaussian beam broadening and scintillation index in anisotropic plasma turbulence

In this paper, new expressions for the long-term beam spreading and scintillation index of Gaussian beams in anisotropic plasma turbulent media are derived on the basis of the anisotropic hypersonic plasma turbulent refractive index undulation power spectrum combined with the Rytov approximation theory. Considering the asymmetry of turbulent eddies in the orthogonal xy-plane throughout the path, two anisotropy factors are introduced to parameterize the anisotropy properties of turbulent cells in the horizontal and vertical directions. The spreading and scintillation index of Gaussian beams in plasma turbulence are calculated, and the propagation characteristics of Gaussian beams in anisotropic plasma turbulence are analyzed. Results show that enhancing the anisotropic properties of hypersonic plasma turbulence can significantly improve the propagation performance of Gaussian beams in hypersonic plasma turbulence. The effect of hypersonic plasma turbulence on Gaussian beam increases with the increase of the refractive index undulation variance and the decrease of the turbulent outer scale and anisotropy parameters. The results provide a theoretical basis for the further study of the propagation properties of electromagnetic waves in hypersonic plasma turbulence.

The analysis of the laser beam shape of the fundamental Gaussian mode by testing the numerical angular spectrum technique

Laser beams are described through the diffraction eigenfunctions or the so-called modes. The principal fundamental Gaussian mode TEM00 is well described analytically in the paraxial approximation of the diffraction integral, and is applied here as the reference for checking the accuracy of the numerical angular spectrum technique. It has been shown that the beam angle divergence larger or smaller influences the Gaussian beam diffraction properties and affects the beam near-field and the far-field. The angular spectrum technique, has been used, with two fast Fourier transformations applied, which turns out to be accurate and fast. The results were simulated with the help of a dedicated computational program written in Borland C++Builder and Matlab software. Some numerical simulation examples of diffraction patterns are also given to illustrate the propagation characteristics of Gaussian beams, where the shape and the intensity distributions of Gaussian beams in the near-field and in the far-field can change.

Analysis of propagation characteristics of Gaussian beams in turbulent plasma sheaths

In this paper, the characteristics of Gaussian beam propagation through turbulent plasma sheath are studied. According to the generalized Huygens-Fresnel principle, the random phase screen is generated by power spectrum inversion method based on the fast Fourier transform. The random phase screen is used to simulate turbulence effect. The thickness of the plasma sheath is of about centimeter order of magnitude. Compared with the single fast Fourier transform algorithm, the double fast Fourier transform algorithm is not prone to under-sampling and can obtain good image results, even if the diffraction distance is 1 mm. Therefore, double fast Fourier transform algorithm is used for investigating the beam propagation between two phase screens. The turbulence effect of the plasma sheath surrounding a hypersonic vehicle is simulated by the multi-random phase screens. When the flight altitude is 45 km and the flight speed is 18 Mach, the intensity of refractive index fluctuation variance ranges from <inline-formula><tex-math id="M2">\begin{document}${10}^{ - 11} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20182169_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20182169_M2.png"/></alternatives></inline-formula> to <inline-formula><tex-math id="M3">\begin{document}$ {10}^{ - 14} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20182169_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20182169_M3.png"/></alternatives></inline-formula> indicated by analyzing the plasma flow field around the hypersonic vehicle. The characteristics of the Gaussian beam propagation through the turbulent plasma are numerically simulated. The results show that the refractive index fluctuation, wavelength and transmission distance are important factors affecting the Gaussian beam quality. The larger the refractive index variance, the more severe the spot dispersion and the more obvious the light intensity fluctuation. As wavelength is longer, the ability of the Gaussian beam to resist turbulence becomes stronger and the dispersion of the light spot and the intensity fluctuation are smaller. The beam distortion and the spot dispersion become more severe as the transmission distance is longer.

Propagation characteristics of Gaussian beams in plasma sheath turbulence

In this study, the new fractal model and power spectrum of plasma sheath turbulence are established based on the fractal dimensions in hypersonic turbulence that were measured through experiments. The expression for beam spot size, scintillation index, angle-of-arrival fluctuation, and beam wander are obtained from the power spectrum. Finally, the propagation characteristics of a Gaussian beam in a turbulent plasma sheath are simulated. The authors’ results indicate that plasma sheath turbulence can lead to amplitude and phase variations. A larger variance in the plasma sheath turbulence causes a more evident refractive index fluctuation and a greater effect on the Gaussian beam propagation characteristics. On the contrary, a larger Reynolds number reduces the effect of the plasma sheath turbulence on the Gaussian beam. This new power spectral model is fundamental to understanding Gaussian beam propagation in plasma sheath turbulence and may provide a reference for the imaging and communication system under the effect of plasma sheath turbulence.

Modeling of Gaussian laser beam reflection from rough sea surface

Studies on the direction distribution of laser beam intensity reflected from the sea surface is important for engineering practice in the area of optoelectronic confrontation on the sea surface. In the traditional theory of electromagnetic scattering from rough surfaces, the scattered field from the sea surface can be obtained by solving the Maxwell's equations. As is well known, it is difficult to solve the Maxwell's equations. Therefore, the numerical calculation method and approximate analytical method are used to obtain the scattered field from the sea surface. However, for the numerical calculation method, it is difficult to meet the computing requirements of large electrically targets such as the sea surface. Meanwhile the approximate analytical method has certain restrictions on the parameters of rough surface in physical approximation. What is more, the inherent error is also caused by the physical approximation. In this paper, we investigate the laser beam reflection from rough sea surface with Monte Carlo method and principles of geometric optics. The rough sea surface which is simulated with the fractal method is divided into a lot of small planes, and the mathematical equations to describe the geometric characteristics of the planes are established in the sea reference coordinate system. After that, based on the simulation of Gaussian beam with Monte Carlo method, the laser beam is divided into a great number of rays and the statistical properties of the rays satisfy the propagation characteristics of Gaussian beam. Then, the laser beam reflection model from the sea surface is derived in the reference coordinate system. The direction distribution of the laser beam intensity reflected from the sea surface is simulated under a certain experiment condition with this model. The results show that the simulation results of laser beam reflection from the sea surface fit the experimental results well.

Propagation characteristics of Gaussian beams through 2 × 2 square matrix circular apertures

Based on the expansion of the hard aperture function into a finite sum of complex Gaussian functions, using Collins formula, the approximate analytical expression of Gaussian beams through 2×2 square matrix circular apertures is derived. Finally, some numerical examples are given to illustrate the analytical results by Matlab. It is shown that the propagation characteristics is related with the propagation distance z, the radius of circular aperture a and the distance d. The results can be directly used in other beams and square matrix apertures, and be applied to control beams and optical system designing.

Propagation characteristics of Gaussian beams through a paraxial ABCD optical system with an annular aperture

By introducing a hard aperture function into a finite sum of complex Gaussian functions, an approximate analytical expression for a Gaussian beam passing through a paraxial ABCD optical system with an annular aperture has been derived. The results could be reduced to the case of circular black screen or circular aperture. Some numerical simulations are also performed and illustrated for the propagation characteristics of a Gaussian beam through a paraxial ABCD optical system with an annular aperture, a circular black screen or a circular aperture.