Bi-static LIDAR systems operating in the presence of oceanic turbulence

Optical turbulence occurring in the oceanic waters may be detrimental for light beams used in the short-link communication and sensing systems, and, in particular, in underwater LIDARs. We develop a theory capable of predicting the passage of light beams through the bi-static LIDAR systems, for a wide variety of optical waves, including partially coherent and partially polarized, and for a wide family of targets. Our theoretical framework is based on the Huygens-Fresnel integral adopted to random media and optical systems described by the $4\times4$ ABCD matrices. The treatment of oceanic turbulence relies on the recently introduced power spectrum model of the fluctuating refractive-index [Opt. Express 27, 27807 (2019)] capable of accounting for different average temperatures of water. We first analyze the evolution of the second-order beam statistics such as the spectral density and the degree of coherence of the beam on its single pass propagation and then incorporate this knowledge into the analysis of the bi-static LIDAR returns

Spatial power spectrum of natural water turbulence with any average temperature, salinity concentration and light wavelength

The power spectrum of water optical turbulence is shown to vary with its average temperature $\left\langle T \right\rangle$ and average salinity concentration $\left\langle S \right\rangle$, as well as with light wavelength $\lambda$. This study explores such variations for $\left\langle T \right\rangle \in \left[ {0\ ^\circ\rm{C},30\ ^\circ\rm{C}} \right]$, $\left\langle S \right\rangle \in \left[ {0\ \rm{ppt},40\ \rm{ppt}} \right]$ covering most of the possible natural water conditions within the Earth's boundary layer and for visible electromagnetic spectrum, $\lambda \in \left[400\ nm, 700\ nm \right]$. For illustration of the effects of these parameters on propagating light we apply the developed power spectrum model for estimation of the scintillation index of a plane wave (the Rytov variance) and the threshold between weak and strong turbulence regimes.Comment: 12 pages, 7 figure

Polarization-induced spectral changes on propagation of stochastic electromagnetic beams

It was shown some years ago that the spectrum of a stochastic scalar field depends not only on the source spectrum but also on the degree of coherence of the source. In this paper we show that there are electromagnetic fields for which not only the state of coherence of the source, but also its degree of polarization affect the spectrum of the radiated field. We illustrate the analysis by diagrams which show the far-zone spectra of some stochastic electromagnetic beams generated by sources of different states of coherence and different degrees of polarization. The spectra of the radiated field depend both on coherence properties of the source and its degree of polarization and are found to be different in different directions of observation

Polarization properties of three-dimensional electromagnetic Gaussian Schell-Model sources

The polarization properties of the recently introduced three-dimensional electromagnetic Gaussian Schell-model sources [Opt. Lett. 42, 1792 (2017)] are examined. Both cases of uniform and non-uniform polarization are considered. The three-dimensional polarization states are characterized via the eigenvalues of a 3×3 source polarization matrix and, more specifically, via the indices of polarimetric purity. We show that the considered sources exhibit a variety of polarization states throughout their volumes conveniently controlled by several physically accessible source parameters.This work was supported by the Air Force Office of Scientific Research (AFOSR) (FA9550-121-0449)

Model for a partially coherent Gaussian beam in atmospheric turbulence with application in Lasercom

Analytic expressions for the mutual coherence function (MCF) and the scintillation index of a partially coherent lowest order Gaussian beam wave propagating through the atmosphere (based on Kolmogorov spectrum model) are developed for the pupil plane of a receiving system. Partial coherence of the beam is modeled as a thin (complex) phase screen with Gaussian spectrum (Rytov theory and ABCD ray matrices are applied). The relation between the second- and fourth-order statistics for a beam with any degree of coherence in the atmosphere is introduced with the help of effective beam parameters, deduced from the free-space MCF. In particular, the scintillation (in weak and strong atmospheric conditions), based on these parameters, is studied as a function of the diffuser\u27s strength and that of the atmosphere. The model is applied for the calculation of the SNR and bit error rates (OOK modulation) of the communication link with diffuser at the transmitter and slow detection system. The improvement of bit error rates is observed in weak and strong atmospheric turbulence. In the weak regime, the optimal diffuser can be found

CONSEQUENCES OF LEVELLING OF THE HIGHER EDUCATION IN RUSSIA IN CONDITIONS OF GLOBALIZATION

In opinion of authors the process of leveling of education quality and level in the developed countries becomes one of doubtful achievements of globalization in the social sphere. Here not only the level of educational and methodical materials provided is averaged, but also the process of teaching itself and its technology. Conceived as the cheap "education "for everyone", distance learning (to be more precise - its technology) gets into the classical educational process at all levels from school to higher education institution. The concept of education  reform (including the highest) carried out in Russia got rid even of the word “expert”. "Cliption" of thinking generated by the Internet is the brand new phenomenon for Russia - phenomenon of intellectual so-called development, or to be more precise - degradation of youth. As a result of such transformations not only the idea of harmonious education and the young generation education is discredited, but the national economy also suffers from the considerable damage

Monte Carlo Simulations of Three-dimensional Electromagnetic Gaussian Schell-model Sources

This article presents a method to simulate a three-dimensional (3D) electromagnetic Gaussian-Schell model (EGSM) source with desired characteristics. Using the complex screen method, originally developed for the synthesis of two-dimensional stochastic electromagnetic fields, a set of equations is derived which relate the desired 3D source characteristics to those of the statistics of the random complex screen. From these equations and the 3D EGSM source realizability conditions, a single criterion is derived, which when satisfied guarantees both the realizability and simulatability of the desired 3D EGSM source. Lastly, a 3D EGSM source, with specified properties, is simulated; the Monte Carlo simulation results are compared to the theoretical expressions to validate the method