Bulletin of the Russian Academy of Sciences: Physics最新文献

The results of lidar measurements of the vertical distribution of optical properties of dust aerosol from the Gobi and Taklamakan deserts in the free troposphere over Vladivostok are presented. A Mi-Raman lidar with a cross-polarization channel was used as an instrument, allowing for the retrieval of vertical profiles of a set of (3β + 2ε + δ) three backscattering coefficients (355, 532, 1064 nm), two extinction coefficients, and one depolarization coefficient at a wavelength of 532 nm. A high depolarization coefficient value (δ = 0.13–0.15), characteristic of submicrometer-sized dust aerosol particles, was observed in the altitude range of 3.00–4.25 km for the dust aerosol from the Gobi Desert. For the aerosol recorded from the Taklamakan Desert, this value was δ = 0.14 in the altitude range of 5–10 km. To obtain information on the spatial distribution of microphysical characteristics, an inversion procedure (3β + 2ε + δ) based on the model of randomly oriented spheroids was used. The complex refractive index within the dust layer had values typical for dust particles, with m_r = 1.48–1.56 and m_i = 0.001 for the aerosol from the Gobi Desert, and m_r = 1.51–1.61 for the aerosol from the Taklamakan Desert.

Efficient near-infrared (NIR) optical devices based on non-linear crystals are demanded for diverse applications ranging from bio-imaging and diagnostic tools to optical parametric conversion. However, significant reflection energy losses, caused by high refractive index of the crystal material, limit their performance. Here, based on example of promising BaGa₄Se₇ nonlinear crystals we demonstrated simple, high-performing and single-step approach to fabricate anti-reflective structures onto their surfaces through direct femtosecond-laser multi-pulse processing. We found that under multi-pulse exposure laser-induced periodic surface structures (LIPSS) with nanotrenches period around 380 ± 10 nm and orientation perpendicular to the irradiating laser beam polarization can be created. The minimal structural damage of the laser-patterned crystals was justified by combining transmission electron microscopy with Raman/X-ray diffraction spectroscopies. Fourier-transform infrared spectroscopy was revealed 1.12-fold transmission increase within the 1.3–2 µm spectral range for LIPSS-textured BaGa₄Se₇ crystal as compared to the untreated one. The proposed method to enhance the efficiency of BaGa₄Se₇ non-linear optical crystal in the practically relevant NIR spectral range holds significant potential for non-linear optical applications.

An experimental study of thermal deformation of a polymer film exposed to laser radiation of different intensity was carried out. The dependence of the radius of curvature of the deformed film on the duration of laser exposure and on the power of radiation was established. The temperature of the laser spot area was measured and the relative change in the film volume was calculated. The coefficient of volumetric expansion of the film material was determined from the obtained data.

Laser-based directed energy deposition process is one of the most promising processes for manufacturing, machining and repair of large-size metal parts of mechanical engineering. The complexity of controlling many changing parameters complicates its practical application. In the article the necessity of using intelligent decision support systems for process engineers of laser-based additive manufacturing is explained. The concept of an ensemble of ontological resources, which is implemented on the IACPaaS cloud platform and can be the basis of such systems, is described. The ensemble includes both a set of related ontologies and domain databases and knowledge bases. The peculiarity of the proposed solutions is that the ontology models are separated from the data and knowledge bases formed on their basis—the target information. Ontology in this approach provides an accurate description of structure, semantics, integrity constraints, as well as defines the rules of formation of target information and its interpretation. Also, one of the main differences from analogues is the explainability of the issued recommendations laid down in the designed decision support system. The developed models, methods and a set of software tools will eliminate some problems of application of additive technologies in industrial production processes, including reducing the requirements for the qualification of technological equipment users.

We studied excitation of fluid flows in sessile liquid droplets by short laser pulses. It is shown that the observed flows are Marangoni thermal flows caused by the temperature gradient of the surface tension coefficient and are excited due to the thermal effect of laser pulses on the liquid in the droplet. The cases of pinned and unpinned contact line, as well as different contact angles and different localization of the irradiating laser pulse within the droplet are investigated. The possibilities of both excitation of internal vortex flows in a stationary droplet and movement of the entire droplet on the substrate are demonstrated. The proposed technique can find application to speed up mixing of multicomponent droplets, as an additional mechanism for tailoring liquid flows in evaporating droplets to control the distribution of impurities deposited on the substrate after droplet drying, as well as for laser-assisted control of droplet motion on superhydrophobic substrates in microfluidics and lab-on-chip systems.

The integration of laser-assisted in-situ synthesis and successive ionic layer adsorption and reaction (SILAR) for the fabrication of supercapacitors on lightweight, flexible substrates is investigated. The focus was placed on the modification of laser-fabricated copper electrodes with zinc hexacyanoferrate (ZnHCF), a Prussian Blue analog known for its exceptional electrochemical properties. The electrochemical performance of the modified electrodes is characterized by cyclic voltammetry and charge-discharge tests, demonstrating the effectiveness of the ZnHCF modification in improving the charge transfer kinetics. The synthesized ZnHCF/Cu composite electrodes exhibit high specific capacitance of 182.3 mF/cm² at a current density of 1 mA/cm² and excellent cycling stability.

The increasing frequency of harmful algal blooms and the growth of associated losses create a need to study and develop new methods for express monitoring of water areas. Using the optical signal of fluorescent algae can be used to track their concentration. By changing environmental conditions, it is possible to control fluorescence spectra to obtain fluorescence parameters that allow distinguishing microalgae from each other by the optical signal. The article demonstrates a technique for measuring fluorescence parameters and shows their characteristic differences from each other. The dynamics of fluorescence during heating at different rates is studied, where lower rates allow achieving less dispersion of fluorescent signals arising during the destruction of algae cells.

While there are many works in the literature that study the effect of such light parameters as wavelength, intensity, photoperiod on plants growth, very little attention is payed to parameter of light polarization. Nevertheless, this light characteristic, as shown in some studies, can have a significant effect on plant development. In most of these studies, the authors note the positive effect of light which is circularly polarized. In one of our previous studies, we showed that maize plants develop better under white linearly polarized light than under non-polarized. In current work, we investigated the effect of linearly polarized light of white, red, green and blue spectral ranges on the dynamics of maize plant development of the Rannyaya Lakomka and Kubansky Sakharny varieties during the week. The results showed that the highest growth rates of maize plants of both varieties relative to non-polarized light treatment were demonstrated by plants grown under green and blue light. Under white light, this effect was less significant, and under red light it was not observed.

The possibility of detection of weak seismic waves in land–sea interface by horizontal fiber-optic interferometric accelerometer is experimentally demonstrated. The use of a passive phase demodulation method with a 3 × 3 fiber-optic splitter ensures high stability of the accelerometer.

The results of an experimental study and theoretical analysis of Bragg diffraction of light on regular domain structures (RDS) with inclined walls in a sample of 5% MgO:LiNbO₃ at different positions of the center of an elliptical probe laser beam with a waist size of 2Δz ≈ 25 µm along the polar Z axis are presented. From the experiments it has been found that the diffraction efficiency η₁(z) for the first spatial harmonic of perturbations of the optical properties created by the walls of the RDS in the crystal is characterized by nonmonotonic behavior with a minimum of η₁ = 0.02 at z = 0.45 mm and two maxima: η₁ = 0.11 at z = 0.19 mm and η₁ = 0.15 at z = 0.80 mm. Under theoretical analysis of the diffraction efficiency at Bragg maxima we have used an approach based on the Fourier decomposition of dielectric tensor perturbations created by inclined walls of the RDS in discrete spatial harmonics with coefficients determined by the components of the continuous angular spectrum. The derived integral expressions for the diffraction field made it possible to describe the dependences of η₁(z) in the Bragg diffraction maximum corresponding to a discrete harmonic with the number m = 1 in the distribution of the perturbations of the optical properties created by RDS with different domain wall parameters. Numerical calculations carried out within the framework of the developed model demonstrated a satisfactory agreement of the theoretical dependence of η₁(z) with the relevant experimental data.