Home – Home – Jornals – Avtometriya 2020 number 4

Recent advances in quantum information are briefly reviewed. The advantages of quantum computers are illustrated using the simplest quantum algorithms. Implementation of quantum computers using ultracold neutral atoms in quantum processors is considered.

In the plasma emission spectra inside the low-emission combustion chamber of a gas turbine engine, the following molecular bands were identified (the most intense edges are given in parentheses): OH (306.1 nm), CH (430.18 nm), H₂O (714-980 nm), C2 (515.55 nm), NH (336 nm), and NO (358.26 nm). This offers a possibility of using the ratio of their intensities to control the operating parameters of the combustion chamber to reduce harmful emissions regulated by ICAO standards. The spectra are recorded by Kolibri-2 spectrometers in two versions: 1) operating spectral range of 190-1100 nm with a resolution of 1 nm and 2) operating spectral range of 190-360 nm with a resolution of 0.2 nm. The plasma emission is coupled to the spectrometer using an optical fiber and a collimator.

The possibility of constructing laser Doppler velocimeters based on the use of a bichromatic source of spatially combined Gaussian or Bessel beams and a two-wave Bragg single-channel acousto-optical modulator with a ratio of ultrasonic wave frequencies equal to the ratio of the wave numbers of diffracting laser beams is discussed. The spatial, chromatic, and frequency structure of the 3D coordinate-measuring basis, formed from Gaussian or Bessel beams by the same sequence of optical elements, and the photoelectric transformation adequate to the structure of light scattered by the medium under study ensure the minimum hardware width of the Doppler signal spectrum and increased noise immunity.

New experimental data on the dynamics of the diffraction efficiency (DE) of superimposed volume reflection holograms with a grating period of ~ 250 nm are obtained when they are simultaneously recorded in the BAYFOL HX TP photopolymer material. The nature and parameters of their mutual influence with a delay in the illumination of one hologram relative to the other are established. It is found that the DE dynamics is practically unaffected by variations in the monomer diffusion time in the interval .12 < tD <0.17 s, but the unsteady behavior of the photopolymerization parameter τp is significantly manifested, which increased from 5 to 15 s in our experiments. The known equations for the photo-induced change in the refractive index of the photopolymer are improved by taking into account the nature of changing of the parameter τp. The calculated dependences of the DE dynamics obtained using the refined formulas are in good agreement with the experimental data (RMS ~ 2%).

Within the framework of the scalar diffraction light theory developed by Kirchhof and Fresnel, specific features of diffraction phenomena in the far zone on cylindrical (metal) objects of small diameters (0.01-0.5 mm) are investigated with allowance for their reflecting properties. A cylinder model in the form of a screen (of zero thickness) is used in the calculations. The reflected component of the field in the far zone is calculated by the stationary phase method. It is shown that the influence of the reflected light wave leads to a noticeable measurement error proportional to the amplitude coefficient of light reflection from the cylinder surface is standard algorithms are used for information processing (valid for objects of the screen type). To reduce this influence, an algorithm is proposed for determining the diameters of such objects with increased accuracy by means of the corresponding processing of the diffraction pattern in the range of angles θ << 3√ λ/R, where λ is the light wavelength and R is the cylinder radius. The results obtained can be used for the development of high-precision diffraction meters for thin cylindrical objects (wires, threads, and fibers).

A method for inspection of the Millimetron Space Observatory telescope multi-element mirror system for its adjustment after deployment in the orbit is proposed in the paper. A laser range finder is used for preliminary inspection of the reflector element positions, and the optical Foucault knife-edge method is applied for the final inspection. The optical scheme of the control system for the final adjustment of the telescope is calculated and presented. The results of modeling images obtained with deflected reflector elements are reported. The results of calculating the optical system implementing the Foucault knife-edge method are presented.

A method and technical solution for laser heterodyne tomography of the scattering properties of thick light-sensitive materials in the reflection mode are proposed. The method is based on acousto-optical scanning of a test reflection grating recorded in the medium and on the layer-by-layer collinear heterodyne analysis of the scattered field. Formulas for estimating the spatial resolution of the method and the test grating period are derived, and the method sensitivity (dependence of the heterodyne signal on the depth of the grating layers) is estimated. The theoretical conclusions are confirmed experimentally.

A system of contactless gun barrel straightness inspection by the structured light method is developed. A design of a compact optical probe, in which a diffractive optical element is used for gun barrel illumination, is proposed and developed. Algorithms for processing of images obtained by means of gun barrel scanning are presented; based on processing results, the 3D shape of the controlled product is retrieved and required geometrical parameters are calculated. Results of the contactless gun barrel straightness inspection system testing by using actual product samples are presented.

A method for determining object deformations using structured lighting is considered. The method is based on the projection of pictures of sinusoidal bands on the surface of the object under study. By using a step-by-step phase shift, one can select information about the phase distribution, which contains data on the surface topography. Comparing the phase distributions before and after the impact on the object, one can determine the field of deformations. A new method for finding phase differences is presented, which significantly reduces the requirements to algorithms for eliminating phase ambiguity. An experimental setup is developed for determining the limit sensitivity of the method in studying deformations of a beam with one of its ends fixed. It is shown that the method sensitivity makes it possible to determine deformations for loads smaller than 10 microns at the free end of the beam.

The possibility of producing film axicons with large focal lengths is experimentally demonstrated. The manufacturing technology includes vacuum deposition of chalcogenide glass layers of variable thickness, which varies linearly depending on the substrate radius. Axicons with focal lengths up to 15 m are obtained.

The conditions of the corona discharge poling of micron guest-host polycarbonate films containing a donor-acceptor dye (polyfluorotriarylpyrazoline-dicyanoisophorone) are determined to create an effective orientation of chromophore molecules. The experiments are carried out using the created triode poling experimental setup with continuous monitoring of the second harmonic generation (SHG) signal from the polymer film directly during the corona poling process. The SHG signal is induced in samples from the first harmonic of a 1064-nm pulsed Nd:YAG laser monitoring the chromophore molecule orientation in the polymer film stimulated by the corona discharge field. The dependences of the SHG signal on the potential of the grid and the needle electrode of the triode system are measured.

A single-frequency thulium-doped distributed-feedback fiber laser is demonstrated. A laser cavity based on a 36 mm long π-phase-shifted fiver Bragg grating (FBG) is inscribed in a heavily doped Tm fiber. Single-frequency radiation with a wavelength of 1919 nm and the maximum output power of 80 mW is generated at the 1.1 W pump power. The lasing linewidth is measured to be about 70 kHz. The relative intensity noise does not exceed 70 dB/Hz with the maximum at a frequency of 1.2 MHz.

Silicon photonics is an important technological platform for the development of various functional optical devices, including perspective types of optical sensors. During the last years, 20% of all publications related to silicon photonics deal with the development of various variants of optical sensors. Their advantage is in the combination of high technical parameters with the possibility of mass production by CMOS compatible technology of microelectronics and nanophotonics. The present review offers a short description of various technological solutions of the last decade responsible for the progress in improving the performances of optical sensors. Special attention is given to new perspective constructions of sensors based on the bimodal technology promising substantial growth of sensitivity owing to equalization of the group delay of different optical modes propagating along the waveguide structure. The review will be useful to Russian and foreign researchers working with sensors.

Methods based on video data processing have demonstrated their effectiveness in many areas of agriculture and forestry. However, they lack classification accuracy for objects and vegetation that can only be achieved by using hyperspectral sensors, but such devices have been quite expensive and difficult to operate until recently; they have been mainly used on satellites and manned aircraft. In recent years, technologies have been proposed for creating more compact and lightweight sensors based on selection of a limited number of spectral intervals and their positions at the design stage. These sensors can be used for scientific or commercial purposes in field conditions; in particular, they can be mounted on drones. In this paper, by an example of 220-channel hyperspectral image processing, we experimentally investigate the possibility of significantly reducing the volume of recorded data by selecting the position and width of a limited number of the most informative spectral channels in solving the problem of crop classification. It is shown that the method used to form the system of informative features has a significant advantage over decimation and is close in efficiency to methods based on the principal component analysis, having a significantly lower required computational complexity.

The influence of the spatial inhomogeneity of the photoelectric characteristics of the focal plane array (FPA) on the quality of detecting small-sized objects in the image it forms is considered. It is shown that the traditionally used two-point correction is not optimal for subsequent matched image filtering aimed at improving the reliability of object detection under the conditions of spatially inhomogeneous FPA intrinsic noise. A two-stage algorithm for constructing a linear spatially invariant matched filter is proposed, which provides a significant increase in the reliability of detecting weak small-sized objects against the background of uncorrelated noise in images containing interference caused by the spatial inhomogeneity of the FPA characteristics.