V. O. Troitskii

Atmospheric bistatic communication channels with scattering. Part 1. Methods of study

The paper considers the methods for theoretical and experimental study of bistatic optical communication schemes. A laboratory model of an optoelectronic communication system has been developed for experimental studies. Copper-vapor laser radiation at a wavelength of 510 nm was used as a source of signals. Test demonstration experiments were performed in the real atmosphere through atmospheric channels with a reflecting surface and a dense nonstationary aerosol-molecular structure. For theoretical studies, software means were developed for numerical statistical estimation of the energy and transfer characteristics of the bistatic atmospheric communication channels by the Monte Carlo method.

Atmospheric bistatic communication channels with scattering. Part 2. Field experiments in 2013

Results of field experiments on the influence of atmospheric conditions and some instrumental characteristics on the quality of information transfer in a bistatic optoelectronic communication system (OECS) operating in the visible wavelengths range are considered. The length of the atmospheric channel reached 17 km. Radiation of a copper bromide vapor laser with a wavelength of 510.6 nm was used as a signal source. It is shown that bistatic or over-the-horizon OECSs can operate both under the conditions of a cloudy and cloud-free atmosphere. Average values and standard deviations of communication errors were estimated under different atmospheric-optical conditions when some characteristics of individual instrumentation units varied.

Propagation of electromagnetic radiation in uniaxial media

A rigorous approach to the solution of Maxwell equations for a monochromatic field in a homogeneous uniaxial medium is considered. The approach is based on using the tensor Green’s function. The general solution satisfying arbitrarily specified boundary conditions is presented. Conditions that must be satisfied by boundary conditions ensuring the existence of the field in the form of an ordinary or extraordinary wave in a uniaxial medium are formulated. These results make it possible to decompose arbitrarily specified boundary conditions, namely, to represent them as a uniquely possible combination of two terms each of which is responsible for the propagation of a wave of only one type. A version of an approximate decomposition of boundary conditions that is applicable to paraxial beams is proposed.

Second harmonic generation of laser radiation in uniaxial crystals. Alternate problem solutions in the assumed field approximation

General questions of the theory of the second harmonic generation of laser radiation in uniaxial crystals are discussed. The derivation of the integral equations determining the form of the interacting fields on an observation plane situated at an arbitrary distance behind the crystal is presented. It is suggested to solve these equations with boundary conditions specified on the same observation plane. It is shown that such a nontraditional choice of the plane of the specification of the boundary conditions allows for a significant simplification of the sought-after second harmonic field representation in the assumed field approximation.

Some problems of optimum focusing in the process of second harmonic generation in nonlinear crystals. Part 1. Mathematical apparatus

The problem of the second harmonic generation (SHG) of monochromatic spatially coherent paraxial radiation in homogeneous uniaxial quadratically nonlinear crystals upon focusing of a beam into a crystal by two crossed cylindrical lenses with different focal lengths is considered theoretically. The aim of the investigations was to determine optimum focusing parameters as functions of the main radiation power. The first part of this paper presents a mathematical apparatus necessary for carrying out the planned investigations. A variant of transforming a system of nonlinear wave equations to a form more convenient for further use is proposed. Some important particular cases admitting simpler solutions are considered. An asymptotically exact analytical solution of the SHG problem is presented.

Europium vapor laser

The results of an experimental study of a gas-discharge Ne–Eu laser are presented. In this work, lasing lines, pulse shapes in the europium atom and ion are identified under the conditions of this experiment. The effects of the buffer gas pressure and pulse repetition rate on the energy characteristics of the laser are ascertained; their optimal values are found. It is shown that the output power is 1 W at the 1759 nm line and 70 mW at the 664.5 nm line for the corresponding transitions under optimal operating conditions.

Some problems of optimum focusing in the process of second harmonic generation in nonlinear crystals. Part 2. Results of numerical calculations

The problem of the second harmonic generation (SHG) of monochromatic spatially coherent paraxial radiation in homogeneous uniaxial quadratically nonlinear crystals upon focusing of a beam into a crystal by two crossed cylindrical lenses with different focal lengths is considered theoretically. Parameters of optimum focusing are determined as functions of the main radiation power. This part of the paper presents main results of numerical calculations. It is shown that, with an increase in the main radiation power, parameters of optimum focusing vary insignificantly at first. Then, beginning from a certain power depending on the initial conditions of the problem, the SHG efficiency maximum becomes attainable with increasingly weaker focusing. The efficiency maximum monotonically increases and probably tends to 100% with an infinite increase in the power.

Radiation of electromagnetic waves in uniaxial media

A rigorous solution for a system of Maxwell equations for monochromatic fields radiated into homogeneous nonabsorbing uniaxial media is presented. Two conditions to be satisfied are determined for the field source distribution functions ensuring the appearance of either only ordinary or only extraordinary waves in the medium. If none of these conditions is satisfied, the distribution function of the field sources can be uniquely represented as a sum of two summands each of which satisfies one of the aforesaid conditions. Thus, one of the summands is responsible for the radiation of the ordinary wave; the second one, for the radiation of the extraordinary wave.

Generation peculiarities of the second harmonics laser radiation at synchronism angles close to 90

The problem of the second harmonic generation in uniaxial crystals at angles of synchronism close to 90° is considered at the approximation of an assumed field. It is shown that this important special case is characterized by a number of distinctive peculiarities, which were not discussed earlier and, more importantly, contradict the commonly held ideas of physics of the considered process.

The influence of the amplitude profile of laser radiation on second-harmonic generation efficiency

The influence of the amplitude profile of the fundamental radiation at the focal waist created by a focusing system on second-harmonic generation (SHG) efficiency has been studied in the negligible pump power depletion approximation. It is shown that highest SHG efficiency is achieved under the conditions where the influence of the walk-off effect is either reduced (cylindrical focusing) or eliminated completely (90° phase matching). The beams with Gaussian transverse amplitude distribution yield maximum SHG efficiency with the lowest intensity of the fundamental radiation in both cases.