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We study the spin angular momentum of a superposition of two vector light beams radial symmetry, one has cylindrical polarization and another – linear. Both beams can have an arbitrary radial shape. An analytical expression is obtained for the spin angular momentum and two its properties are proven. The first one is that changing weight coefficients of the superposition does not changes the shape of the spin angular momentum density distribution, whereas the intensity shape can change. The second property is that the maximal spin angular momentum density is achieved when both constituent beams in the superposition have equal energy.

In this work, using the Richards-Wolf formalism, we consider the sharp focusing of optical vortices with hybrid polarization, which combines the properties of azimuthal and circular polarizations. It is shown that these beams have a number of unique properties: the intensity pattern in such beams is rotating with distance from the focal spot and the longitudinal component of the spin angular momentum is asymmetrically shaped.

The density of the longitudinal component of the spin angular momentum (SAM) vector is calculated for a paraxial vector Gaussian beam with a periodic one-dimensional modulation. For the beam under consideration, the SAM in the initial plane is zero and the polarization is inhomogeneous and linear. When this beam propagates in free space, due to periodic modulation it is effectively divided into two beams with left-handed and right-handed elliptical polarization. That is, in the cross section of the beam, regions with spins of different signs are separated in space, which is a manifestation of the spin Hall effect. This beam can be formed using a metasurface whose transmission periodically depends on one coordinate.

A numerical model is developed for simulation of the propagation of a light bullet in LiF crystal and the formation of a colored track. The model reproduces the previously observed longitudinal oscillations in the concentration of color centers in the track and oscillations in the track width. For the first time, the phase shift between these oscillations is numerically reproduced.

We propose a method of the formation of spiral-shaped microreliefs in thin films of chalcogenide glasses. The method is based on projection lithography using laser beams with a structured polarization distribution. To control the polarization of the initial laser beam, a spatial light modulator HOLOEYE LC 2012 is used. It is shown that changing the contrast of the mask images displayed on the modulator display affects the convexity/concavity of the formed profiles. This approach can be effectively used for the direct laser fabrication of more complex nano-/microelements, as well as their arrays.

The possibilities of using spatial separation of channels in a multimode fiber are considered. When information is transmitted through a multimode fiber, a large number of errors arise due to mode dispersion, mode-to-mode interference and other sources. It is shown that if the fiber data transmission utilizes not an image corresponding to the original digital array but an image hologram, it is possible to use a specific property of holography – the divisibility of a hologram, thus ensuring the restoration of the original image from a highly distorted hologram or its fragment. The virtual optical object for which a hologram is constructed is a point source on a black background, and information is included in the coordinates of the radiation source. The result of encoding is the simplest hologram – a Fresnel zone plate, with the coordinates of the plate center carrying the encoded information. At the receiver, the purpose of decoding is not to restore the brightness of each point of the transmitted hologram, but to calculate the coordinates of the center of the Fresnel zones. This is what makes this method highly resistant to all types of distortion. A description of the numerical simulation is given, the results of which show that when moving from using a single-mode optical fiber for digital data communication to a multimode fiber for image transmission with the number of modes N=4096, a 128-fold increase in the transmission speed can be achieved, with mode dispersion distorting up to 20% of the received image.

In this study, an algorithm based on convolutional neural networks is employed as an interrogation method for a fiber specklegram sensor. This algorithm is compared with conventional interrogation methods, including correlation between images, measurement of optical power, and radial moments. Fiber specklegram sensors have room for improvement as conventional methods only consider a single characteristic of the specklegram for variable prediction, thus failing to leverage the full spectrum of information within the specklegram. Consequently, the approach put forth here introduces a convolutional neural network for the extraction of specklegram features, accompanied by an artificial neural network for variable regression. The specklegrams used in this investigation are obtained through simulating temperature disturbances in a multimode fiber using the Finite Elements Method. The results reveal prediction RMSE errors ranging from 10.26°C for the first radial moment to 1.42°C for the proposed algorithm. These findings underscore the effectiveness of the proposed strategy in enhancing sensor performance and robustness, all while upholding their cost-efficiency.

The modern demands for miniaturization of optoelectronic devices, in particular, for the UV range, are inextricably linked with the improvement of fabrication technologies for the corresponding photonic nano/micro objects and the study of their radiative properties. In this work, the method of pyrolytic carbothermal synthesis, which is a modification of the thermal evaporation method, was used to fabricate microcrystalline ZnO films with laser properties. The influence of the size and packing type of ZnO microcrystallites in the films on their emissive properties were revealed. The films with relatively large microcrystallites (10–15 µm in size on average) were found to exhibit UV amplified spontaneous emission at room temperature. The possibility of additional enhancement of this emission and its two-threshold behavior in loose-packed regions of such films were found for the first time. It was shown that the observed phenomenon is due to the competition between two gain mechanisms, which are assumed to arise predominantly in different regions of microcrystallites as a result of exciton-phonon and exciton-electron interaction processes. As the temperature decreases, the dominant gain mechanism gradually changes to exciton-exciton scattering, regardless of the type of film structure. The results obtained open up the possibilities of the thermal evaporation synthesis to a wider extent and can be useful in interpreting the optical gain mechanisms in ZnO micro- and nanostructures.

Unmanned Aerial Vehicle (UAV) remote sensing is a commonly used technical means in modern science and technology, but currently, remote sensing images captured by UAVs need to be spliced to obtain more comprehensive information. However, current image stitching techniques generally have shortcomings such as a small number of extracted features, low matching accuracy, and poor stability. To address the above issues, this study proposes an improved remote sensing image mosaic model on the bias of the Scale Invariant Feature Transform (SIFT) algorithm. Firstly, in this study, aiming at the problem that traditional SIFT cannot meet the requirements of feature extraction and matching for unconventional remote sensing images and special texture images, normalized cross correlation (NCC) and Forstner operator are introduced to optimize it, namely, a SIFT-NCC model is constructed. On this basis, for remote sensing images with high resolution and a wide range, this study further proposes a remote sensing image automatic mosaic model that combines point features and line features. That is, a linear segment detector (LSD) is introduced to extract the line features of remote sensing images. The experimental verification results of the final SIFT-NCC-LSD show that the matching accuracy for remote sensing images with different characteristics can reach over 95 %. Therefore, SIFT-NCC-LSD has good applicability.

The paper considers a number of issues related to the calculation of the local entropy in a sliding window for image processing tasks. A new algorithm for entropy estimation is proposed, which has several times lower computational complexity than the known ones. The algorithm is based on the approximate representation of the histogram in the form of a truncated series expansion over some system of orthogonal basis functions, recursive calculation of the coefficients of this expansion in a sliding window and subsequent recalculation of the coefficients into the entropy estimate. Questions of an orthogonal basis selection for representing the local histogram as a truncated series are considered and the appropriateness of using the Haar basis is shown. A technique of constructing hierarchical approximator, which realizes fast recalculation of histogram decomposition coefficients into entropy value, is described. The theoretical statements of the paper are verified by experiments on the Earth remote sensing images.