We propose a method for designing diffractive optical elements (DOEs) with a smooth phase function generalizing harmonic diffractive lenses and intended for generating a prescribed intensity distribution at several harmonic wavelengths. In this method, the phase function is represented as an expansion over a certain set of smooth and differentiable functions. The expansion coefficients are considered as optimization parameters and are calculated using a gradient method from the condition of minimizing an error function describing the deviation of the generated intensity distribution from the prescribed one. We present examples of calculating harmonic DOEs with phase functions modulo 2πM, M>1 represented as a sum of B-splines. We show that in order to obtain good performance of a harmonic DOE, the error function has to take into account not only the intensity distribution generated at the central wavelength but also the distributions formed at the other harmonic wavelengths of interest. The obtained theoretical results are confirmed by the results of an experimental investigation, including the fabrication of the designed harmonic DOE using the direct laser writing technique and measurement of the generated intensity distributions.

A comparative analysis of photodetectors based on TiS2 nanosheets and on TiS2 nanosheets functionalized with silver nitrate is carried out. TiS2 nanosheets were synthesized by a chemical vapor transport technique, followed by a 1-hour ultrasonication treatment. The obtained solution was deposited between interdigitated electrodes fabricated on the surface of a flexible substrate using a dielectrophoresis process. Polyethylene terephthalate was used as a flexible substrate material. The characteristics of the fabricated photodetectors were determined by illuminating them with tunable-power laser light at 1064 nm. A significant effect of silver nitrate particles scattered in the volume of the photodetector sensitive material on its efficiency is observed. The superiority of the photodetector based on TiS2 nanosheets functionalized with silver nitrate is demonstrated. This photodetector demonstrates a significant response for all the laser light powers used (11.6, 19.6, 51, 100, and 150 mW), shows fast response (0.23±0.01 s) and recovery (0.49±0.02 s) times, coupled with high sensitivity (260∙103±7∙103 A/W), quantum efficiency (303∙103±8∙103 A/W∙nm) and detectivity (3.10∙1013±0.09∙1013 Jones) at an incident laser light power of 11.6 mW. The results obtained in this study can be used for the development and optimization of modern optoelectronic devices.

This paper presents findings from a spaceborne Earth observation experiment utilizing a novel, ultra-compact hyperspectral imaging camera aboard a 3U CubeSat. Leveraging the Offner optical scheme, the camera’s hyperspectrometer captures hyperspectral images of terrestrial regions with a 200 m spatial resolution and 12 nanometer spectral resolution across a 400 to 1000 nanometer wavelength range, covering 150 channels in the visible and near-infrared spectrums. The hyperspectrometer is specifically designed for deployment on a 3U CubeSat nanosatellite platform, featuring a robust all-metal cylindrical body of the hyperspectrometer, and a coaxial arrangement of the optical elements ensures optimal compactness and vibration stability. The performance of the imaging hyperspectrometer was rigorously evaluated through numerical simulations prior to construction. Analysis of hyperspectral data acquired over a year-long orbital operation demonstrates the 3U CubeSat’s ability to produce various vegetation indices, including the normalized difference vegetation index (NDVI). A comparative study with the European Space Agency’s Sentinel-2 L2A data shows a strong agreement at critical points, confirming the 3U CubeSat’s suitability for hyperspectral imaging in the visible and near-infrared spectrums. Notably, the ISOI 3U CubeSat can generate unique index images beyond the reach of Sentinel-2 L2A, underscoring its potential for advancing remote sensing applications.

This paper presents the results of a study of the catalytic activity of bimetallic materials synthesized based on Vulcan XC-72 carbon black modified with nickel, cobalt, and molybdenum in the electrochemical oxygen reduction reaction. The studies of the synthesized catalysts by adsorption–desorption of nitrogen in vacuum show that they are mesoporous and possess low porosity and surface area. After modification with metals, the surface area of the catalyst and pore volume decrease. The Raman spectra of the samples evidence probable formation of intermetallics or mixed molybdenum oxides on the surface of the MoCo/C and NiMo/C catalysts, which is in agreement with the published data. Scanning electron microscopy shows the formation of spherical metal parties on amorphous Vulcan XC-72. All the studied bimetallic catalysts possess similar kinetic characteristics of the electrochemical oxygen reduction reaction; nevertheless, NiMo/C and NiNi/C catalysts manifest a higher activity. The verification of the robustness of operation of the synthesized catalysts shows their high corrosion resistance.

In this work, we studied the photoinduced polarimetric and optical properties of the photosensitive carbazole-based azopolymer prepared in the form of thin films. Poly-N-(2,3-epoxypropyl)carbazole was used as a polymer matrix, which was copolymerized with the commercially available azo dye Solvent Yellow 3. Thin films of µm thicknesses were obtained by home-made rod-coating techniques. Polarization holographic recording was applied for direct diffraction gratings patterning. The polarization states of the recording beams were P–P, S–S, ±45° and left-right circular. The optical path of the probe beam passing through investigating media is defined by the summary changes in surface topography and volume anisotropy. The periodically modulated polarization/amplitude interference patterns produced by the gratings were investigated by in situ measurements of the diffraction efficiency (DE) kinetics in the first diffraction order at the DE saturation value. The surface relief was measured by AFM. A comparison of the behavior of azopolymer films during the recording of diffraction gratings with different polarization configurations of recording beams was carried out. The presented results confirm the possibility of recording not only the amplitude and phase of light, as in scalar holography, but also the polarization states of interfering beams. The angular dependences of the probe beam azimuth and ellipticity were analyzed, and some peculiarities of azopolymer photoinduced changes are discussed.

Catalysts based on mesoporous silica gel doped with cerium, terbium and modified with silver (Ce–Ag/MPS, Tb–Ag/MPS) were obtained by the template method. The physicochemical characteristics of the obtained catalyst were studied by low-temperature nitrogen adsorption–desorption, scanning electron microscopy, X-ray diffraction analysis, inductively coupled plasma mass spectrometry, and IR spectrometry. The possibility of using the obtained samples as effective and selective catalysts for the hydrogenation of 1-hexyne/1-hexene and 1-heptyne/1-heptene hydrocarbon mixtures (with 30

Bi- and trimetallic catalysts based on multi-walled carbon nanotubes (MWCNT) and metal (Me) phthalocyanines (Pc) (MePc) (MWCNT–CoPc–NiPc, MWCNT–CuPc–NiPc, MWCNT–CoPc–CuPc, and MWCNT–CoPc–CuPc–Pd) for electrochemical oxygen reduction reaction (ORR) were synthesized by high-temperature synthesis at 1000°C in an inert atmosphere. The obtained materials were characterized by scanning electron microscopy (SEM), low-temperature nitrogen absorption–desorption, and Raman spectroscopy. The change in textural characteristics and morphology of electrocatalysts during high-temperature synthesis was studied. It was shown that the nature of the metal significantly changes the physicochemical characteristics of electrocatalysts based on carbon nanotubes. The electrochemical experiment was carried out in the linear voltammetry algorithm using a three-electrode chamber with a rotating disk electrode. The main characteristics of the process of electroreduction of oxygen from an alkaline electrolyte—limiting diffusion current, potential half-waves, and initial reaction potential—were determined. MWCNT–CoPc–CuPc–Pd catalyst was found to exhibit the highest activity in the reaction of electrochemical oxygen reduction in an alkaline liquid, reaching high efficiency and corrosiveness as with platinum catalysts, with a decrease in activity after 1000 cycles of less than 7

The paper proposes approaches for the classification of high-resolution hyperspectral images in the problem of classification of soil species classification. A spectral-spatial convolutional neural network with compensation for illumination variations is used as a classifier. The effectiveness of the proposed approach in the problem of classification of hyperspectral images of soils obtained by a scanning type hyperspectrometer is shown. A multiclass neural network is compared with an ensemble in which the results of a multiclass neural network are refined by several binary classifiers. It is shown that the use of normalization of illumination inhomogeneity and the use of an ensemble of convolutional spatial-spectral neural networks can significantly increase the accuracy of soil type classification.

In this paper, we present a hybrid refractive-diffractive lens that, when paired with a deep neural network-based image reconstruction, produces high-quality, real-world images with minimal artifacts, reaching a PSNR of 28 dB on the test set. Our diffractive element compensates for the off-axis aberrations of a single refractive element and has reduced chromatic aberrations across the visible light spectrum. We also describe our training set augmentation and novel quality criteria called "false edge level" (FEL), which validates that the neural network produces visually appealing images without artifacts under a wide range of ISO and exposure settings. Our quality criteria (FEL) enabled us to include real scene images without a corresponding ground truth in the training process.

Detailed automated analysis of crop images is critical to the development of smart agriculture and can significantly improve the quantity and quality of agricultural products. A hyperspectral camera potentially allows to extract more information about the observed object than a conventional one, so its use can help in solving problems that are difficult to solve with conventional methods. Often, predictive models that solve such problems require a large dataset for training. However, sufficiently large datasets of hyperspectral images of agricultural plants are not currently publicly available. Therefore, we present a new dataset of hyperspectral images of plants in this paper. This dataset can be accessed via URL https://pypi.org/project/HSI-Dataset-API/. It contains 385 hyperspectral images with a spatial resolution of 512 by 512 pixels and spectral resolution of 237 spectral bands. The images were captured in the summer of 2021 in Samara and Novocherkassk (Russia) using Offner based Imaging Hyperspectrometer of our own production. The article demonstrates the work of some basic approaches to the analysis of hyperspectral images using the dataset and states problems for further solving.

We consider the formation of forked diffraction gratings on the surface of a multilayer structure based on chalcogenide glass semiconductors As2S3 and a-Se is. The distribution of electric field components upon interference of beams with different polarization states is analyzed theoretically. The possibility of direct holographic writing of diffraction gratings with a “forked” structure is demonstrated. The parameters of vortex laser beams generated by the microrelief formed are examined.

The main obstacle to the widespread dissemination of fuel cells is the high cost, so researchers are actively searching for ways to replace the expensive platinum catalyst with cheaper analogs. In this paper we studied the Ag- and Pd-containing carbon catalysts based on carbon nanotubes and graphene oxide. The study of the textural characteristics of the catalysts showed that the greatest specific surface area has a catalyst based on MWCNT containing 10% silver, all synthesized catalysts are mainly mesoporous, and the content of micropores is insignificant. Raman spectroscopy and SEM data indicate a significant change in the structure of the modified carriers compared to pure MWCNT and GO. An electrochemical experiment was performed and linear voltammetric diagrams were obtained and compared with the voltammetric diagrams obtained on the platinum catalyst. GO_Ag 10% and MWCNT_Ag 10% Pd 10% are closest in the values of kinetic parameters in both kinetic and diffusion regions. GO_Ag 10% has the highest initial potential Eonset = −0.145 V and MWCNT_Ag 10% Pd 10% has the highest half-wave potential E½ = −0.23 V. The studied catalysts have characteristics comparable to those presented in the literature.

Blood vessel visualization technology allows nursing staff to transition from traditional palpation or touch to locate the subcutaneous blood vessels to visualized localization by providing a clear visual aid for performing various medical procedures accurately and efficiently involving blood vessels; this can further improve the first-attempt puncture success rate for nursing staff and reduce the pain of patients. We propose a novel technique for hyperspectral visualization of blood vessels in human skin. An experiment with six participants with different skin types, race, and nationality backgrounds is described. A mere separation of spectral layers for different skin types is shown to be insufficient. The use of three-wavelength indices in imaging has shown a significant improvement in the quality of results compared to using only two-wavelength indices. This improvement can be attributed to an increase in the contrast ratio, which can be as high as 25%. We propose and implement a technique for finding new index formulae based on an exhaustive search and a binary blood-vessel image obtained through an expert assessment. As a result of the search, a novel index formula was deduced, allowing high-contrast blood vessel images to be generated for any skin type.

Present work deals with the development of high-speed NO2sensor based on functionalized Single Walled Carbon Nanotubes (SWNTs). To improve the sensing properties of SWNTs, SWNTs is functionalized with the enzyme N-benzyloxycarbonylglycine (Z-Gly-OH). Various parameters of the functionalization process such as time and temperature are also optimized and analysed in detail. Z-Gly-OH has created a functionalization of the 1,3-dipolar cycloaddition type, which is capable of doing modification in the properties of CNTs while maintaining the electronic properties of CNTs. The functionalization with Z-Gly-OH makes it possible to obtain amino groups on the surface of nanotubes in the absence of a solvent, while during this reaction it is possible to obtain intermediate functionalization in the form of benzyl carbamate, which can affect the sensitivity of sensors. In order to develop solid state device, Ti(8 nm)/Au(100 nm) interdigitated electrodes (IDEs) are fabricated on thermally oxidized Si substrate by using standard photolithography process. Dielectrophoresis is employed for deposition of as-functionalized SWNTs (f-SWNTs) between the IDEs. The gas sensing performance of as-developed is tested for NO2 gas as function of NO2 concentration (70 ppm to 20 ppm). As-developed gas sensor shows fast response/recovery (~ 88 s/95 s) as well as high sensitivity 27%. In order to analysed selectivity of as-developed gas sensor, the cross sensitivity has been observed for carbon monoxide (CO) and Methane (CH4). Before development of sensor, as-prepared f-SWNTs is analysed by SEM, Raman and FT-IR for its morphological and structural characteristics.

The paper presents a study of various approaches to the classification of soil covers based on neural network algorithms using hyperspectral remote and proximal sensing of the Earth. The spectral distributions were recorded in the laboratory using an Offner imaging scanning hyperspectrometer. Spectral-spatial characteristics of nine soil samples from various parts of a farming land in the Samara region were experimentally studied. Using a method of energy dispersion microanalysis, the correspondence between the hyperspectral data and the chemical composition of the samples taken was established. Based on the data obtained, a neural network-aided classification of soil samples was implemented depending on the content of constituent elements such as carbon and calcium. A normalized spectral-spatial convolutional neural network was used as a classifier. As a result of the work, an approach to the classification of high-resolution hyper-spectral images based on the refinement of a multiclass convolutional neural network using an ensemble of binary classifiers is proposed. It is shown that the classification of soil samples by carbon and calcium content is carried out with an accuracy of 0.96.

The article presents the results of a study of hyperspectral imaging in microscopy to assess pathological changes in unstained medical micropreparations. Hyperspectral imaging was carried out using a system of synchronous shooting and movement of a movable table combined with a stepper motor. To improve the quality of the obtained images, software correction of the illumination of the spectral channels was used. The classification was carried out by a convolutional neural network. This method may be promising for assessing pathological changes in clinical practice. Experimental studies were carried out on histological preparations with different types of tissues without staining with contrasting medical dyes. To assess the reliability of the classification method, a comparison was made with the standard method using staining of the studied samples.

Single- and double-beam formation of diffraction microstructures in carbazole-containing azopolymer films is presented. The possibility of recording single microroughnesses by a focused vortex laser beam with linear and circular polarization is shown. The analysis of the relief shape microstructures on the state of polarization. A double-beam method of creation of diffraction lattices is presented, in which a spatial light modulator is used for the formation of the vortex phase. The evaluation of the diffraction efficiency of the formed periodic optical structures on the duration of the exposure is performed.

A device for visualization of blood vessels in the human skin is presented. A diffractive optical element is used to locate blood vessels in the skin image. It has been shown that visualization of blood vessels is most effective in the form of obtaining an index image at wavelengths of 735 nm and 835 nm. The index is calculated using a formula similar to the NDVI formula. The work also uses an application software that is used to solve the problems of spectral analysis.

Guided-mode resonant gratings with spatially varying parameters are widely used as linear variable optical filters, and their behavior is often described using the so-called local periodic approximation, in which the structure is locally replaced by a strictly periodic grating with the period coinciding with the "local" period at the considered point. In this work, we investigate the optical properties of guided-mode resonant gratings with the period linearly varying along the periodicity direction. Using full-wave numerical simulations, we show that when the period change rate is relatively high (about 0.5-1 mu m/mm for the considered structures), the local periodic approximation becomes inapplicable, and the linewidth and the line shape of the resonances depend significantly on the period change rate. We qualitatively explain the appearance of an asymmetric non-Fano line shape with secondary maxima by analyzing the local photonic band structure of the studied varying-period gratings. For a more accurate description of such gratings, we develop a spatiotemporal coupled-mode theory, the predictions of which are in good agreement with the rigorous numerical simulation results. The validity of the derived theoretical model is additionally confirmed by a proof-of-concept experiment with a varying-period guided-mode resonant grating. The obtained results may find application in the design of compact linear variable filters based on resonant gratings with spatially varying parameters.

A new element is proposed for producing an azimuthally polarized beam with a vortex phase dependence. The element is formed by two conical surfaces in such a way that the optical element resembles a mountain with a crater on top, like a volcano (volcanic cone is volcone). The element in the form of a refractive bi-conic axicon is fabricated by diamond turning, in which an internal conical cavity is made. Polarization conversion in this optical element occurs on the inner surface due to the refraction of beams at the Brewster angle. The outer surface is used to collimate the converted beam, which significantly distinguishes the proposed element from previously proposed approaches. The paper describes a method for calculating the path of beams through a refractive bi-conic axicon, taking into account phase and polarization conversions. In the case of incident circularly polarized radiation, azimuthally polarized ring-shape beam radiation is generated at the output. The proposed element is experimentally made of polymethyl methacrylate on a CNC milling machine. The experiment demonstrates the effectiveness of the proposed element.