Home – Home – Jornals – Avtometriya 2024 number 3

The operation of a two-level gas laser in schemes with single-sided and double-sided transverse diode pumping is investigated theoretically. If the reflection coefficient of the output mirror is not too small, analytical formulas are obtained that describe the operation of a two-level gas laser with single-sided and double-sided diode pumping and make it possible to determine any laser energy characteristics and to find optimal parameters of the working medium and pump radiation that are required for the most effective laser operation. It is shown that the generation efficiency of a two-level gas laser can be increased by 11-20% when switching from single-sided to double-sided pumping.

A coherent fiber-optic system for transmitting OFDM signals is considered. The spectrum of nonlinear phase noise arising in an optical fiber under nonlinear operating conditions of the optical path is investigated. It is shown that the spectrum of nonlinear phase noise consists of frequency components both at the fundamental frequency of the channel and at the combination frequencies falling within the band of OFDM channel signals. Estimation formulas are given for determining the noise immunity of channel signals by calculating the Q-factor depending on the transmission system parameters, in particular, on the number, modulation format (QPSK, M-QAM), and power of channel signals. An example of calculating the Q-factor for channel signals of the QPSK format is given. The need to limit the optical power level in the fiber is shown in order to achieve the required signal quality indicator; for example, when transmitting a multichannel signal over a 100-km fiber, it is necessary to limit the power level to 6.5, 7.4, and 8.8 dBm when using error correction methods FEC, HD-FEC, and SD-FEC, respectively

A solution to the direct ellipsometry problem is presented for a single-layer model consisting of an isotropic substrate and an anisotropic film in the case of the orientation of the optical axis of the film in the plane of incidence. Analytical expressions for calculating the ellipsometric parameters of such a structure are obtained. A simple numerical algorithm is proposed for determining the ordinary ( n_o ) and extraordinary ( n_e ) refractive indices of a bulk crystal under various measurement conditions. The inverse problem of determining n_o, n_e, and film thickness d when changing the azimuth of the optical axis is considered. The correlation of the required parameters for such a problem is discussed.

The question of the correctness of using a harmonic signal to simulate the operation of measuring phase systems, for example, adaptive optics systems that measure and correct turbulent distortions, is investigated. The time evolution of phase distortions for an optical wave as it propagates in a turbulent atmosphere is estimated. When analyzing the evolution of phase distortions in an optical wave caused by the action of turbulence, the ratio of the dispersions of the first and second derivatives is calculated for the increment of phase distortions over a certain time interval. The magnitude of this ratio is compared with the same value obtained in modeling temporary distortions when using a harmonic signal. When modeling the time evolution of phase distortions using harmonic signals, it is necessary to take into account not only the first derivative of this increment, but also, at a minimum, the second derivative.

Acousto-optic terahertz radiation deflectors based on an optically isotropic medium are characterized by a low number of resolved light spots. Substantial improvement of the deflector characteristics can be achieved by using a sectioned phased ultrasonic transducer. In this paper, an angular-frequency dependence for such a deflector is analytically obtained for the first time, and the position of the working point on it is specified taking into account the influence of the gap between the sections of the ultrasound transducer.

Methods and systems for generating hyperspectral data based on spectral scanning and without image scanning are considered. This is due to the transition in many practical problems from aerospace to “ground-based” hyperspectral imaging methods. Options for implementing spectrum separation devices, a key element of modern viewing hyperspectrometers, are presented. The main parameters and technical characteristics of absorption, interference, and liquid crystal filters are presented, and their fundamental capabilities are shown. The cross section of the filtered light beam and its angular aperture in such devices can be very large, which makes them suitable for studying objects of weak radiation. Tunable filters without mechanical movements of structural elements based on high-speed acousto-optical devices and planar Mach-Zehnder interferometers with electrostatic control are considered. Currently, their maximum spectral resolution is less than 1 nm for the visible and near-infrared ranges.

A speed comparison is made of various multi-stage procedures for localization of pulsed-point sources that reveal themselves by generating instantaneous pulses at random times. The results of the study confirm the high efficiency of the universal procedure for multi-stage localization of a uniformly distributed point source in cases where no additional a priori information about the power and possible location of the searched object within the search interval is available. A new quasi-optimal localization method that increases the search efficiency in the presence of a priori information about the distribution function and power of the searched source is proposed and justified.

In the process of conducting biomagnetic (magnetocardiographic) studies, it is necessary to take into account the spatial features of the input converter-heart structure: the depth of occurrence, location and orientation of the current dipole, and the geometric configuration of the input converter. The spatial spectral density of the source has a pronounced dependence on the depth of its occurrence. Various issues of derivation and analysis of the spatial frequency transformations of the input converter and its spatial filtering properties are considered in the present study.

The methods of bandwidth selection of the kernel functions of the regression estimation of the probability density of a one-dimensional random variable are investigated. Regression estimation of the probability density is a modification of the Rosenblatt-Parzen statistics and is used in processing of large-volume statistical data. Its synthesis is based on compression of the initial sample by means of decomposition of the range of values of the random variable. The elements of the resulting data array are the centers of the sampling intervals and the frequency of belonging of the values of the random variable chosen from the initial sample to them. This information is sufficient to estimate the probability density of the random variable in the form of a nonparametric regression. Therefore, it becomes possible to select the bandwidths of the kernel functions of the regression estimate from the condition of the minimum error of the desired probability density approximation. The traditional approach to optimizing nonparametric estimation of the probability density is based on minimizing its mean square deviation. The approximation properties of regression estimation of the probability density are analyzed when using the considered methods of its optimization.

Comparative results of a real flight experiment and a flight simulation of a small unmanned aerial vehicle are presented. A longitudinal motion control system is developed using a total energy approach. The outputs of the total energy controller are converted into control signals for deflecting the aircraft rudders in pitch and roll, as well as into an engine thrust command. The model of the aircraft motion is obtained in the form of tabular dependencies of the dimensionless coefficients of forces and moments on the angles of attack, slip, and elevon deflection. The total energy control method is tested for a small flying-wing-type aircraft. During the simulation process, two modes are used: capturing and maintaining the altitude and capturing the angle of inclination of the trajectory; in the flight experiment, the model of capturing and maintaining the altitude is used. The structure of the control system and the results of modeling and a real flight experiment are presented.

The problem of the control system design for electrohydraulic test benches for strength and life tests of aircraft structures is considered. It is proposed to use a control algorithm with iterative learning to improve the accuracy of the formation of a given cyclogram of force loading of mechanical structures. The results of numerical simulation of a test bench control system with iterative learning are presented, as well as the results of experimental testing of the proposed algorithm on a single-channel test bench. The results of modeling and experiments on the test bench show the possibility of increasing the accuracy of forming a given force loading cyclogram based on the proposed approach. The results obtained make it possible to automate the process of setting up regulators for electrohydraulic drives of strength test benches, as well as to speed up the process of carrying out endurance and static strength tests of aircraft structures.

Various issues of development of an algorithm for motion of the measuring module of an automated system for nondestructive quality testing of the soldered joints of the engine nozzle are discussed. The object of testing is identified as that with a complex geometric shape with flaws in the soldered joints of the test object formed during the manufacturing process. The defects studied in this paper are the “dry joint,” “partially dry joint,” and “cold lap.” The relevance of the development, as well as the problems of production and testing of engine nozzles, which do not allow the required defects to be identified at the early stages of manufacturing assembly units without destroying the integrity of the engine nozzle, are substantiated. The existing approaches are described in terms of the choice of methods and means for nondestructive testing of engine nozzles of complex geometric shapes; their advantages and disadvantages are identified. The existing problems in terms of automation of the pulse-echo and through-transmission methods of ultrasonic testing are analysed; the advantages and disadvantages of the proposed methods are identified. The main factors that reduce the probability of detecting defects are determined, namely, the instability of the acoustic contact between the transducer and the test object, as well as the deviation of the acoustic axis of the transducer from the normal to the surface of the test object. The requirements to the algorithm of motion of the measuring module of an automated nondestructive testing system with feedback based on the signal amplitude measured during scanning the signals from the structural elements of the internal structure of the engine nozzle are determined.