Optoelectronics, Instrumentation and Data Processing (v.53, #3)

Time-Optimal algorithms of searching for pulsed-point sources for systems with several detectors by A. L. Reznik; A. V. Tuzikov; A. A. Soloview; A. V. Torgov (203-209).
Time-optimal algorithms of localization of pulsed-point sources randomly distributed over the search interval and detected due to generation of instantaneous pulses (delta functions) at random time instants are developed. Optimal search procedures ensure prescribed accuracy of localization and depend on the number of receivers in the detector.
Keywords: optimal search; pulsed-point source; localization of the object; minimum time

Computationally simple algorithms are proposed to estimate the local frequency vector of a real two-dimensional signal with slowly varying parameters in the presence of additive Gaussian noise. The rough most likely estimate of the frequency vector is refined using three-point interpolation algorithms and the singular value decomposition of a 3 × 3 matrix of discrete Fourier transform coefficients. The results of computer simulation are presented showing the efficiency of the algorithms for analyzed fragments of small size.
Keywords: frequency estimation; two-dimensional real signal; interpolation algorithms; discrete Fourier transform coefficients; singular value decomposition of matrices

Determination of the three-dimensional velocity vector using the laser doppler measurements of unevenly sampled components by A. V. Klimov; S. V. Dvoinishnikov; V. G. Meledin; D. V. Kulikov; S. V. Krotov; I. V. Shchepikhin (216-222).
This paper describes the method for determining the three-dimensional velocity vector of the flow using the laser Doppler measurements of unevenly sampled components. This method is based on the filtering and linear interpolation of the measured velocity components in the circuit channels. It is shown in the numerical simulation and physical experiment that the method error does not exceed 2% and the results of interpolation with respect to the closest points are several times greater.
Keywords: laser Doppler meter; three-dimensional velocity vector; uneven sampling; filtering; multidimensional interpolation

Using signals of special form in multi-frequency eddy current testing by A. V. Egorov; V. V. Polyakov; A. A. Lependin; Ya. I. Gracheva (223-229).
An eddy current testing method based on the use of an exciting signal of special shape is proposed. Subsequent digital processing of the detected output signal makes it possible to calculate the measuring sensor parameters at different frequencies and to construct an experimental hodograph of the sensor–test object system. Experiments performed for materials with different physical and geometrical characteristics of constructing hodographs have shown that the proposed method provides a reliable separation of the main factors affecting the results of multi-frequency eddy current measurement. The results can be used in automated systems for inspection and non-destructive testing of materials and products.
Keywords: automation of measurements; eddy current method; inspection of materials; digital signal processing

This paper considers issues related to the identification of the parameters and form of the probability density function of generally non-Gaussian additive and multiplicative noise affecting the signal. The results of numerical simulation of methods for estimating the information parameters of random processes with a non-Gaussian probability density function for a finite sample.
Keywords: distribution parameters; non-Gaussian probability density function; additive noise; multiplicative noise

Algorithm of fatigue crack detection and determination of its tip position in optical images by S. V. Panin; V. O. Chemezov; P. S. Lyubutin; V. V. Titkov (237-244).
An algorithm of fatigue crack detection in optical images taken in fatigue tests of materials is proposed and tested. The algorithm is designed for automation of measurements of the crack propagation parameter and tracing the crack tip position in the course of cyclic loading for the purpose of shifting the optical system with respect to the examined sample surface to the “region of interest.” It is found that the coordinates of the image fragment containing the crack can be determined with a mean error of 1.93% of the total size of the raster. Testing of the algorithm on model images shows that the mean error of determining the crack tip position is smaller than 56 pixels.
Keywords: image processing; optical flow; fatigue crack; contour analysis; mathematical morphology

This paper touches upon the synthesis of high-quality images in real time and the technique for specifying three-dimensional objects on the basis of perturbation functions. The recursive search method for the image elements of functionally defined objects with the use of graphics processing units is proposed. The advantages of such an approach over the frame-buffer visualization method are shown.
Keywords: perturbation functions; set-theoretic operations; tile visualization technology

A monochromator capable of suppressing spurious laser radiation to a level required for low-frequency (<100 cm−1) Raman spectroscopy is proposed. It has a high spectral resolution, contains a small number of optical elements, and can be easily included into the experimental optical scheme. The effect of using this monochromator in low-frequency Raman spectroscopy is illustrated by examples with test samples.
Keywords: Raman spectroscopy; Raman scattering; laser radiation

This paper presents a method of improving the accuracy of a circular laser system in fabrication of large-diameter diffractive optical elements by means of a polar coordinate system and the results of their use. An algorithm for correcting positioning errors of a circular laser writing system developed at the Institute of Automation and Electrometry, SB RAS, is proposed and tested. Highprecision synthesized holograms fabricated by this method and the results of using these elements for testing the 6.5 m diameter aspheric mirror of the James Webb space telescope (JWST) are described..
Keywords: diffractive optical elements; laser writing; nanopositioning

Potential accuracy of methods of laser Doppler anemometry is determined for the singleparticle scattering mode where the only disturbing factor is shot noise generated by the optical signal itself. The problem is solved by means of computer simulations with the maximum likelihood method. The initial parameters of simulations are chosen to be the number of real or virtual interference fringes in the measurement volume of the anemometer, the signal discretization frequency, and some typical values of the signal/shot noise ratio. The parameters to be estimated are the Doppler frequency as the basic parameter carrying information about the process velocity, the signal amplitude containing information about the size and concentration of scattering particles, and the instant when the particles arrive at the center of the measurement volume of the anemometer, which is needed for reconstruction of the examined flow velocity as a function of time. The estimates obtained in this study show that shot noise produces a minor effect (0.004–0.04%) on the frequency determination accuracy in the entire range of chosen values of the initial parameters. For the signal amplitude and the instant when the particles arrive at the center of the measurement volume of the anemometer, the errors induced by shot noise are in the interval of 0.2–3.5%; if the number of interference fringes is sufficiently large (more than 20), the errors do not exceed 0.2% regardless of the shot noise level.
Keywords: laser Doppler anemometry; maximum likelihood estimates; potential measurement accuracy

This paper describes the nonradiation (Forster) energy transfer between a dye J-aggregate and closely located nanoparticles possessing the properties of two-level systems. Nanoparticles can be quantum dots (QDs) or a spherical symmetric package of atoms. The dynamics of the process is described by deriving the equations that characterize the density matrix dynamics in a two-level medium and the evolution of exciton pulses in an extended quasi-one-dimensional dye J-aggregate. It is shown that effective controlled resonant transfer of the energy stored in QDs is implemented in the system and manifested in the amplification of the exciton pulses. In turn, there is a possibility of the reverse process of exciton energy transfer in partial inversion of two-level transitions of QDs. The results of this paper are confirmed by the experimental data from the literature.
Keywords: tubular J-aggregates; quantum dots; Forster mechanism; nonradiation energy transfer; numerical solution

This paper presents the results of measurement of the surface potential and the dwell time of Rb and Na atoms on the surface of S-52 molybdenum glass. It is found that at temperatures below the glass transition temperature, the temperature dependence of the dwell time of Rb atoms is well described by the Arrhenius formula. The surface potentials for Rb and Na are measured to be 0.67 and 1.37 eV, respectively. At temperatures above the glass transition temperature, the dwell time of these atoms increases abnormally. The reason for this is that during impact of an atom on the surface of molten glass, it can penetrate into the volume of the window and then return by diffusion and desorb from the surface. In this case, the dwell time of the atom on the glass is determined by the diffusion time and can be very significant, despite the relatively low potential barrier at the surface and high temperature.
Keywords: collision of atoms with glass surface; dwell time; probability of adsorption and desorption

This paper describes the method for recovering digital holograms obtained at small angles between interfering wave fields. The technique for obtaining data on the phase of the wavefront reflected from the object is under consideration.
Keywords: hologram; digital holography; phase shifting interferometry

Capacitive MEMS accelerometers for measuring high-g accelerations by I. L. Baginsky; E. G. Kostsov (294-302).
A possibility of creating a capacitive accelerometer for measuring high-g accelerations (up to 106 g and higher) is discussed. It is demonstrated that insertion of a thin electret film with a high surface potential into the gap between the electrodes ensures significant expansion of the frequency and amplitude ranges of acceleration measurements, whereas the size of the proposed device is smaller than that of available MEMS accelerometers for measuring high-g accelerations. A mathematical model of an electret accelerometer for high-g accelerations is developed, and the main specific features of accelerometer operation are analyzed.
Keywords: MEMS accelerometer; electrostatics; electret; high-g accelerations

This paper describes the study of the surface morphology of BaF2 epitaxial films grown by means of molecular beam epitaxy in various growth regimes on a CaF2/Si(100) surface, which is performed by means of atomic force microscopy. The CaF2 layers were obtained on a Si(100) substrate in a low-temperature growth regime (T s = 500 °C). The technological regimes of growth of BaF2 continuous films with a smooth surface on CaF2/Si(100), suitable as buffer layers for the subsequent growth of PbSnTe layers or other semiconductors, such as A4B6, and solid solutions based on them.
Keywords: molecular beam epitaxy; calcium fluoride; barium fluoride; silicon; buffer layer; AFM; surface morphology