Computer Optics

590-597

Authors: D. A. Bykov, L. L. Doskolovich

Diffraction of a 3D optical beam from a resonant multilayer structure (phase-shifted Bragg grating) is considered. It is shown that the said structure enables optical computation of the spatial Laplace operator of the electromagnetic field components of the incident beam. The computation of the Laplacian is performed in reflection at normal incidence. Presented numerical results demonstrate high quality of the Laplace operator computation. The beam transformation performed in transmission is also investigated.

606-613

Authors: S.S. Stafeev, L. O’Faolain, M.I. Shanina, A.G. Nalimov, V.V. Kotlyar

Using a binary microlens of diameter 14 µm and focal length 532 nm (numerical aperture NA = 0.997), we focus a 633-nm laser beam composed of a mixture of radially and linearly polarized waves obtained by reflection of a linearly polarized Gaussian beam from a gold-coated subwavelength binary four-zone diffractive optical microelement (micropolarizer) of size 100×100 µm to a near-surface, near-circular focal spot of size (0.37±0.02)λ and (0.39±0.02)λ, where λ is wavelength. A linearly polarized light beam forms an elliptical focal spot with diameters (0.35±0.02)λ and (0.41±0.02)λ. Both focal spots have the area of 0.133λ². Subwavelength focusing using two microoptical components (a binary microlens and a micropolarizer) is suggested for the first time.

619-622

Authors: D.I. Zavershinskiy , N.E.Molevich

Earlier, we demonstrated the possibility of energy transfer from unstable acoustic waves into Alfven waves due to a process of three-wave interaction of collinear waves. In this paper, we briefly discuss cooling mechanisms and possible heating scenarios of an optically thin plasma medium. The upper layers of the solar atmosphere have been chosen as the model medium. By the use of two cooling function models we obtain temperature intervals in which the instability can take place and calculate acoustic increments for all heating scenarios.

629-637

Authors: S.A. Degtyarev, A.V. Ustinov, S.N. Khonina

We show that the near-field nanofocusing of the electromagnetic field is possible to implement not only by means of metallic but also dielectric structures with sharp edges. The effect of the extraordinary enhancement of the longitudinal electric field component near the sharp edges of an optical element microrelief is shown using vector Rayleigh-Sommerfeld integrals. A finite element method is used for modeling the diffraction of the electromagnetic radiation by the edges of high-refractive-index metal and dielectric structures. It is shown that the focal spot size (full width at half-maximum) depends on the radius of curvature of the sharp tip. An optical scheme for sharp focusing, which consists of a concentrator collecting and directing the radiation onto a nano-focuser, is offered. A refractive axicon is suggested as the concentrator that directs the radiation on its vertex where an aluminium or silicon nanosphere is located (a nanofocuser). Illumination of this focuser by an optical vortex beam provides the nanofocusing with high diffraction efficiency. It is necessary to illuminate an axicon by a vortex beam of the first order or by a radially polarized beam. The scheme proposed is able to confine the radiation within a light spot of size l/400 at the half maximum of the intensity.

643-650

Authors: A.O. Gorbunova, I.P. Zavershinskii, N.E. Molevich, D.P. Porfirev

Numerical simulation of non-stationary vortical plasma-gas-dynamic structures formed in a swirl flow in the open tube under the RF-electromagnetic field is conducted. It is shown that when the external RF-field coincides with the resonator’s eigenfrequency, an abrupt jump of gas-dynamic fluctuations and corresponding changes in the discharge structure take place.

658-662

Authors: A.A. Kovalev, V.V. Kotlyar, A.P. Porfirev

With use of a liquid crystal phase-only spatial light modulator, we generate form-invariant Half-Pearcey laser beams (HP-beams), which were recently proposed by the present authors [Computer Optics, v. 38, no. 2 (2014)]. It is experimentally shown that upon propagation the HP-beams preserve their shape up to a scale and rotate by 180 degrees. These beams have the ability to auto-focus and reconstruct their intensity pattern after partial distortion by an amplitude defect (property of self-healing). The amplitude and phase of the HP-beam were encoded with the modified two-phase algorithm. Ignoring the amplitude and using only the phase leads to greater distortions of the HP-beam comparing with the two-phase encoding algorithm.

670-680

Authors: S.N. Khonina, A.V. Ustinov, S.A. Degtyarev

We consider the diffraction of Gaussian beams by a cylindrical axicon whose numerical aperture (NA) is close to or higher than a limiting value (when the incident wave is assumed not to pass through an element). Three models of diffraction were considered: the ray approach, the vector wave theory with a thin optical element approximation and the solution of Maxwell’s equations by the finite elements method. Although in the ray approach the limiting NA corresponds to the total internal reflection (TIR), the analysis of the ray path has shown that with increasing NA (narrowing axicon’s angle) a proportion of energy leaks through the lateral sides, forming a diverging beam. In the wave theory, energy dissipation in lateral directions also occurs, but evanescent waves play a special role in the element’s near-field zone. In this case, the analytical estimations for the electric field components have been obtained in a thin element approximation. Application of the finite element method to Maxwell’s equations has shown that for optimal concentration of energy at the refractive element’s tip its NA should be increased (by narrowing the axicon’s angle or by increasing the material refractive index) only until the TIR occurs. The further increase of the NA results in both the reflection of rays from the flat surface and their output from the lateral sides.

686-688

Authors: I.V. Alimenkov, Y.Z. Pchelkina

Solutions of the expanded pulse-propagation equation are derived in elementary functions in optical fibers for competing nonlinearit.

695-703

Authors: A.G. Poleshchuk, A.G. Sedukhin, V.I. Trunov,V.G. Maksimov

A theoretical and experimental study of a Hartmann sensor intended for measurements of light beam wavefronts and implemented on the basis of multielement amplitude masks with apodized apertures is presented. We perform a comparative analysis of the optical performance of the amplitude masks with hard-edge circular apertures and half-tone masks (HTMs) with apodized apertures forming smooth fast decaying optical responses on a photosensor. A technique for fabricating chromium HTMs is developed, which is based on laser thermochemical method of recording. This technique includes two main stages: first – the exposure of a chromium film by a focused laser beam, whose power is varied in a smooth and nonlinear manner versus the required density of HTM’s structure, and second – the developing of the film in a selective etcher. Specimens of HTMs consisting of 64×64 Gaussian apertures were fabricated and applied in a modified Hartmann sensor to measure the wavefront of powerful laser systems.

710-716

Authors: A.V. Belashov, N.V. Petrov, I.V. Semenova

A method for calculating the difference between two arbitrary spatial phase distributions reconstructed from digital holograms is presented. The method is promising for application in double-exposure digital holographic interferometry, especially for the evaluation of phase variations in heavily noised or speckle-structure-modulated digital holograms, because it does not use the phase unwrapping procedure for each reconstructed spatial phase distribution. Instead, by analogy with classical double-exposure holographic interferometry, an interference pattern formed by two reconstructed object waves is calculated first. The interferogram thus obtained is then processed as a digital hologram by the same method that was used for reconstruction of physically recorded holograms. The advantages of the proposed method are demonstrated by both by the numerical computation of the difference of the phase distributions of speckle-structure-modulated wavefronts and the experimental observation of the laser-induced temperature gradients in an aqueous solution of a photosensitizer.

722-726

Authors: A.P. Porfirev, R.V. Skidanov

We demonstrate optical trapping and movement of a carbon nanoparticle agglomeration with both a single optical bottle beam and arrays of such traps. Diffractive optical elements (DOE) designed by a method based on a superposition of the Bessel beams were employed for the generation of the optical traps. Due to the structure of the generated traps, we were able to carry out a three-dimensional movement of trapped microscopic objects.

737-742

Authors: R.V. Kutluyarov, A.H. Sultanov, V.H. Bagmanov

We consider interaction of polarization-mode dispersion (PMD), Kerr-nonlinearities and chromatic dispersion and its effect on the quality of WDM-transmission in a fiber link. We simulate the propagation of RZ- and NRZ-coded signals in a multispan link with optical amplification and chromatic dispersion compensation. For some fiber realizations signal impairments reduction occurs in the case of PMD and nonlinearities interaction as compared to the case of nonlinear transmission with no PMD. This signal enhancement is related to the pulse compression and this phenomenon is determined by the frequency dependence of PMD.

749-756

Authors: A.A. Zvekov, A.V. Kalenskii, A.P. Nikitin, B.P. Aduev

The radiative transfer equation in a slab with Fresnel boundaries was solved by the spherical harmonics method in the case of a transparent medium containing aluminum nanoparticles. A computer program was developed, the angular radiance distribution on the slab boundaries and in the slab center were calculated. It was concluded that Fresnel boundary conditions make the angular distribution on the slab boundaries asymmetric. The use of angular radiance distribution for solving the reverse problems of scattering spectroscopy was discussed.

763-769

Authors: A.N. Agafonov, B.O. Volodkin, A.K. Kaveev, B.A. Knyazev, G.I. Kropotov, V.S. Pavelyev, K.N. Tukmakov, Yu.Yu. Choporova

Experimental results on forming pre-given laser modes from an illuminating Gaussian beam of a terahertz Novosibirsk Free Electron Laser (NovoFEL) at the wavelength of 141 mm by use of binary silicon diffractive optical elements are presented. The experimental results are in good agreement with the results of computer simulation.

777-781

Authors: L.L. Doskolovich, E.A. Bezus, D.A. Bykov

We analyze the performance of a diffraction-grating-based Offner spectrometer. We use the paraxial approximation to derive analytical expressions for the spatial and spectral point spread function for each diffraction order. We show that a disruptive effect of the diffraction orders overlap occurs. However, it can be compensated for by means of simple image post-processing.

790-793

Authors: E.V. Myasnikov

This paper considers two approaches to the hierarchical decomposition of the feature space to improve the efficiency of the non-linear dimensionality reduction method. The first approach suggested by the author of the paper is based on the decomposition of the original feature space using hierarchical clustering. The second original approach is based on a hierarchical decomposition of the target space by using a KD-Tree. The approaches analyzed are evaluated in terms of the efficiency of the non-linear dimensionality reduction method.

804-810

Authors: N.L. Kazanskiy, V.I. Protsenko, P.G. Serafimovich

Comparison of two streaming systems: Apache Storm and IBM InfoSphere Streams was performed in solving image sliding window filtering task. Analysis was focused on two parameters: throughput and memory consumption. Profiling was held under CentOS operating systems running on two virtual machines for each system. First, the most cheap in developing cost realizations were compared. After analysis optimization of memory consumption was performed. Final suggestions on applicability of two systems were made at the end of the article.

818-824

Authors: М.А. Shcherbakov, A.P. Panov

Different approaches to the construction of digital nonlinear filters that operate by use of local image properties are offered. Structures of nonlinear filters with variable nonlinear-component weight and parametric adaptation are considered. The effectiveness of the proposed methods of filtering is illustrated by the examples of the additive Gaussian and impulse noise suppression.

833-842

Authors: M.A. Dryuchenko, A.A. Sirota

A steganography algorithm based on a relatively low-frequency spatial deformation of full color image fragments is considered. Correlation properties for the color channels of images are used for extraction of hidden data. Results of the algorithm application are presented.

851-855

Authors: N.Yu. Ilyasova, A.V. Kupriyanov, R.A. Paringer

The computer diagnostic system of eye diseases is considered. To improve the quality of diagnostics we propose an algorithm for the informative features formation, using methods of discriminant analysis. The method for receiving an informtiveness estimation is described. The research confirming the efficiency of the formed features for classification of images of an fundus was conducted by means of classification by support vector machine. The algorithm possesses a sufficient level of universality and may be applied to increase the informtiveness of any feature set.

865-870

Authors: A.Yu. Kruchinin

We introduce an algorithm for the recognition of two-dimensional industrial codes DataMatrix that would allow one to identify codes applied by a shock-point or a drip method on the surface with a complex background. The algorithm can be adapted to a varying background by changing the binarization mode.

881-885

Authors: M.S. Kasparyan

We introduce a generalized sine-cosine transform (GSCT). Analytical conditions of orthogonality of these transformations are derived. A theorem that allows one to find the relation between the GSCT coefficients in the orthogonal case is proven. Fast algorithms for computing the GSCT are considered and their complexity is analyzed.