Computer Optics

791-795

Authors: O. Korotkova

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.

803-811

Authors: A.B. Sotsky, A.V. Shilov, L.I. Sotskaya

Relations are obtained that make it possible to compute the field of the wide-band terahertz pulse in capillary waveguides with a hollow core and a metalized cladding. From the standpoints of maximization of the pulse energy transfer coefficient and time-domain spectroscopy of air, two types of waveguides are investigated: hollow waveguides with a metalized cladding and dielectric-lined waveguides whose hollow core is separated from the metal by a dielectric layer. It is shown that the efficiency of the waveguides of the second type is higher due to their quasi-single-mode operation.

820-830

Authors: D.G. Denisov

A dynamic interferometry method for controlling nano-scale local deviations of optical surfaces from a prescribed profile is developed, theoretically substantiated, and experimentally verified on the basis of an algorithm for calculating an objective function, defined as the spectral density of a one-dimensional correlation function. Theoretical and experimental approaches to determining the root-mean-square error when finding local deviations of the optical surfaces for the element diameters ranging from 100 mm to 1,000 mm are presented, while taking into account the non-excluded systematic and random error components in determining the objective function.

837-841

Authors: V.D. Paranin, S.V. Karpeev, O.G. Babaev

A method for the investigation of birefringence of mechanically free parabolic gradient-index lenses based on the astigmatic transformation of a zero-order Bessel beam has been experimentally verified. Special features of the alignment of the optical setup are described and practical recommendations for selecting the setup components are given. By the example of a quarter-wave lens, we show experimentally that the optical path difference can be reliably measured within a 0.05λ0 accuracy. A significant difference between the birefringence properties of the gradient-index lenses in their central and edge regions is confirmed.

848-855

Authors: S.P. Murzin, G. Liedl

A use of laser technology it is progressive in the welding of dissimilar materials. Pulsed laser welding of an aluminum alloy AK4 and a titanium alloy VT5-1 was performed. Processing conditions were determined, the realization of which during melting of materials in the heat-affected zone makes it possible to obtain a homogeneous structure without voids and shells, potentially producing sufficiently sound welded joints. To create the required power density distribution across the laser beam, it was found expedient to use diffractive optical elements. Aluminum and copper were welded by continuous laser beam. It is determined that laser action with its well-defined and precise localized heat input makes it possible to significantly reduce the growth of intermetallic compound layers.

864-868

Authors: K.M. Bulatov, Y.V. Mantrova, A.A. Bykov, M.I. Gaponov, P.V. Zinin, A.S. Machikhin, I.A. Troyan, V.I. Batshev, I.B. Kutuza

In this paper, we demonstrate that combining a laser heating (LH) system with a tandem acousto-optical tunable filter (TAOTF) allows us to measure the temperature distribution (TD) across a laser-heated microscopic specimen. Spectral image processing is based on one-dimensional (1D) non-linear least squares fitting of the Planck radiation function. It is applied for determining the temperature T at each point (x, y) of the specimen surface. It is shown that spectral image processing using the 1D non-linear least squares fitting allows measurement of the TD of the laser-heated microscopic specimen with higher precision and stability than those of the conventional linear least-squares fitting of the Wien approximation of Planck’s law.

875-887

Authors: A.V. Nikonorov, M.V. Petrov, S.A. Bibikov, V.V. Kutikova, A.A. Morozov, N.L. Kazanskiy

In recent years, several pioneering works were dedicated to imaging systems based on simple diffractive structures like Fresnel lenses or phase zone plates. Such systems are much lighter and cheaper than classical refractive optical systems. However, the quality of images obtained by diffractive optics suffers from stronger distortions of various types. In this paper, we show that a combination of the high-precision lens design with post-capture computational reconstruction allows one to attain a much higher image quality. The proposed reconstruction procedure uses a sequence of color correction, deconvolution, and a feedforward deep learning neural network. An improvement both in lens manufacturing and in image processing may contribute to the emergence of ultra-lightweight imaging systems varying from cameras for nano- and picosatellites to surveillance systems.

897-904

Authors: N.A. Smelkina, R.N. Kosarev, A.V. Nikonorov, I.M. Bairikov, K.N. Ryabov, A.V. Avdeev, N.L. Kazanskiy

We propose a method of statistical shape modeling applied to reconstructing anatomical structures with deformations. This method is promising for modeling deformed body parts that have a certain normal shape. The method of statistical shape modeling allows one to reconstruct a deformed object using information about the normal shape of the body part and its undeformed fragment, while taking into account peculiar individual features and the variability relative to the average shape.

913-919

Authors: Y.D. Vybornova, V.V. Sergeev

In this paper, we propose a new digital watermarking method for protecting of vector data in geographic information systems. The method is based on a combination of two novel approaches. Firstly, the watermark information is embedded into the polygon map objects by cyclically shifting the list of vertices of each polygon. Secondly, instead of a bit vector, a raster image superimposed on the map is considered as a watermark. The major advantage of this method is that it does not distort the map by altering the coordinate values. A simple example demonstrates the method efficiency, as well as the robustness of the embedded watermark against geometric transformations usually performed when working with map data: translation, scaling, rotation and cropping.

931-937

Authors: I.V. Borisova, V.N. Legkiy, S.A. Kravets

In this paper, a problem of automatic target tracking in complex natural backgrounds is considered. Target detection is performed in each frame of a video sequence by the elementwise comparison with a reference image. The proposed method is based on the representation of every pixel as the orientation of the luminance gradient in the vicinity. The vicinities are divided into classes depending on their orientation. In addition to the classes of anisotropic vicinities, a class of vicinities with an isotropic structure is introduced. The classes are numbered and the number of the vicinity class is used as a feature of the point of interest. Thus, the original gray-scale image is transformed to a pseudo-image in which the detection procedure is carried out. The encoded image is then scanned using a reference image. The elementwise comparison of the reference image with the current fragment is performed in a feature space. As a result, a comparison matrix is formed, each element of which is the number of matching elements of the reference image and the current image fragment. The position of the reference image is determined by the maximum value of the comparison matrix. A special rule of reference image overwriting, the so-called dynamic proximity measure, is used to achieve stable tracking. The testing results have shown that with our approach the object tracking is more stable in comparison with the use of normalized correlation.

950-956

Authors: T.V. Yakovleva

The paper presents a new technique for the accurate measurement of the phase difference between two quasi-harmonic optical signals through analyzing and processing their envelope values obeying the Rice statistical distribution. With this technique, the envelope values of three signals are measured: two initial quasi-harmonic signals for which the phase difference is measured and a third signal formed as superposition of the first two. The phase shift under measurement is calculated from simple geometrical considerations as the angle of a triangle formed by the amplitude values of the reconstructed undistorted signals. The fundamental distinction of the proposed technique consists in the fact that the phase characteristics are derived from the amplitude measurements alone, thus significantly mitigating the requirements imposed on the equipment and simplifying the practical implementation of the method. It is proposed that the undistorted amplitudes should be estimated using methods of the Rician data analysis. The paper provides a strict mathematical analysis of the problem and computer simulation results. The ability to conduct accurate phase shift measurements based on the proposed method is useful for a wide range of applied tasks solved in numerous ranging and communication systems.

963-972

Authors: A.V. Vorobev, G.R. Vorobeva

We present and describe a method to conduct correlation and amplitude-frequency analysis of the observational data of geomagnetic variations and space weather that is based on the combined use of a concept of single information space, models and methods of wavelet and Fourier analysis, and geo-information technologies. The method includes formalized elements of mathematical and methodological support for conducting amplitude-frequency and correlation analysis of the observations of geomagnetic variations and space weather and is verified by means of a prototype in-house platform-independent web-oriented geoinformation system GEOMAGNET (https:// www.geomagnet.ru). The proposed method is verified using data obtained from the magnetic observatories of the INTERMAGNET network and space weather data from the artificial Earth satellite ACE. Results of the observation, automated correlation and amplitude-frequency analysis of signals that provide information on the geomagnetic field and space weather variations at specified time intervals both on the Earth's surface and in near-Earth space are discussed and evaluated.