Search

The development of various nanomaterials production technologies has led to the possibility of producing nanoparticles (NPs) and nanostructures, which can find a wide range of applications, from the fabrication of microelectronic devices to the improvement of material properties and the treatment of cancer. The unique characteristics of nanoparticles are primarily due to their small size, which makes size control important in their preparation. Modification of nanoparticles by laser irradiation and obtaining desired nanoparticle properties is a promising approach because of its ease of implementation. The purpose of this review is to analyze the works devoted to the study of laser-induced heating and melting of nanoparticles, to collect information and evaluate the results of using this method for functionalization and modification of metallic nanoparticles, and to discuss promising directions for the use of this technique. [ABSTRACT FROM AUTHOR]

The paper presents and discusses the results of simulation of the current-voltage characteristics of an avalanche photodiode carried out in the SPICE program. The simulations take into account the influence of the directed energy of the electromagnetic field used in modern DEW (Directed-Energy Weapon), in the form of laser optical radiation and HPM (High Power Microwave) radiation, on the characteristics of the photodiode. The calculations were made using the model of the considered diode developed by the authors.

In this paper, the technique of surface absorption of a uniform laser radiation is used to illuminate the upper surface of a thermoelastic layer whose properties are temperature-dependent utilizing the new modification of Green's and Lindsay's thermoelasticity theory. The upper surface of the layer is exposed to heat losses and the lower surface is considered insulated, while both are traction free. The general solution of the problem obtained by applying Laplace transform in which whose inverse obtained computationally. In addition to the usual temperature-dependent consideration, we also investigate the case of temperature-dependent absorption coefficient of the surface. [ABSTRACT FROM AUTHOR]

Experimental study has been made of the ignition of a subcritical microwave discharge at pressures in the range 55–79 Torr with the initiation by pulsed laser radiation (58 mJ in a pulse). A rise of 36% in the critical pressure was obtained to form the discharge with the orientation of the laser beam along the vector of the microwave-field strength. Computer modeling has shown that upon the traversal of a focused laser beam, a highly conductive laser trail can be formed with a peak ionization degree as high as 10%, which, for a period of the order of 1 μs, locally enhances the electric microwave field up to supercritical values. [ABSTRACT FROM AUTHOR]

The goal of this paper is to construct a novel model based on the recently modified Green and Lindsay model to study the bio-thermo-mechanical responses induced by uniform laser radiation in a thermoelastic biological skin tissue. The biological tissue’s upper surface experiences heat loss, whereas the lower surface is insulated and both are traction-free. A general solution for this model was achieved by applying the Laplace transformation while its inversion was computationally attained by employing the Riemann sum approximation formula. A numerical example is used to show the consistency of the new model with earlier models where the graphical behaviour of our findings is concise with the well-known physical facts and some of them could be useful in dermatology and cosmetic.

The development of various nanomaterials production technologies has led to the possibility of producing nanoparticles (NPs) and nanostructures, which can find a wide range of applications, from the fabrication of microelectronic devices to the improvement of material properties and the treatment of cancer. The unique characteristics of nanoparticles are primarily due to their small size, which makes size control important in their preparation. Modification of nanoparticles by laser irradiation and obtaining desired nanoparticle properties is a promising approach because of its ease of implementation. The purpose of this review is to analyze the works devoted to the study of laser-induced heating and melting of nanoparticles, to collect information and evaluate the results of using this method for functionalization and modification of metallic nanoparticles, and to discuss promising directions for the use of this technique.

This paper studies the dynamics of the development of laser breakdown plasma in aqueous colloids of dysprosium nanoparticles by analyzing the time patterns of plasma images obtained using a high-speed streak camera. In addition, the distribution of plasma flashes in space and their luminosity were studied, and the amplitude of acoustic signals and the rate of generation of new chemical products were studied depending on the concentration of dysprosium nanoparticles in the colloid. Laser breakdown was initiated by pulsed radiation from a nanosecond Nd:YAG laser. It is shown that the size of the plasma flash, the speed of motion of the plasma–liquid interface, and the lifetime of the plasma flash decrease with an increasing concentration of nanoparticles in the colloid. In this case, the time delay between the beginning of the laser pulse and the moment the plasma flash reaches its maximum intensity increases with increasing concentrations of nanoparticles. Varying the laser fluence in the range from 67 J/cm2 to 134 J/cm2 does not lead to noticeable changes in these parameters, due to the transition of the breakdown plasma to the critical regime. For dysprosium nanoparticles during laser breakdown of colloids, a decrease in the yield of hydrogen peroxide and an increase in the rate of formation of hydroxyl radicals per water molecule, characteristic of nanoparticles of rare earth metals, are observed, which may be due to the participation of nanoparticles and hydrogen peroxide in reactions similar to the Fenton and Haber–Weiss reactions.

A finite-volume algorithm with splitting over physical processes is developed to model nonstationary problems of laser thermochemistry with catalytic nanoparticles in subsonic gas flows. Two-phase flows in a heated pipe with laser radiation and radical kinetics of nonoxidative methane conversion are simulated. It is shown that the conversion of methane at the outlet of the pipe is more than 60% with predominant formation of ethylene and hydrogen. [ABSTRACT FROM AUTHOR]

The primary focus of the present contribution is to develop a new system of differential equations describing the nonlocal thermoelasticity theory. The problem deals with the thermoelastic interaction in a nonhomogeneous thermoelastic layer induced by absorbing penetrating laser radiation throughout its volume. The heat conduction equation has been formulated in the context of memory dependent three-phase lag model. The surfaces of the layer are thermally insulated and free of traction. Employing the integral Laplace transform technique, the solutions of the field quantities have been achieved in the transformed domain. The corresponding solutions in the space–time domain have been derived using the numerical inversion of the Laplace transform by Riemann-sum approximation technique. The numerical estimates of the field quantities have been depicted graphically to address the effects of nonlocality and memory effects on the temperature profile, displacement and stress components. The effect of the delay time, nonhomogeneity and various choices of linear and nonlinear kernel functions in the heat transport law have also been reported. [ABSTRACT FROM AUTHOR]

This paper studies the dynamics of the development of laser breakdown plasma in aqueous colloids of dysprosium nanoparticles by analyzing the time patterns of plasma images obtained using a high-speed streak camera. In addition, the distribution of plasma flashes in space and their luminosity were studied, and the amplitude of acoustic signals and the rate of generation of new chemical products were studied depending on the concentration of dysprosium nanoparticles in the colloid. Laser breakdown was initiated by pulsed radiation from a nanosecond Nd:YAG laser. It is shown that the size of the plasma flash, the speed of motion of the plasma–liquid interface, and the lifetime of the plasma flash decrease with an increasing concentration of nanoparticles in the colloid. In this case, the time delay between the beginning of the laser pulse and the moment the plasma flash reaches its maximum intensity increases with increasing concentrations of nanoparticles. Varying the laser fluence in the range from 67 J/cm2 to 134 J/cm2 does not lead to noticeable changes in these parameters, due to the transition of the breakdown plasma to the critical regime. For dysprosium nanoparticles during laser breakdown of colloids, a decrease in the yield of hydrogen peroxide and an increase in the rate of formation of hydroxyl radicals per water molecule, characteristic of nanoparticles of rare earth metals, are observed, which may be due to the participation of nanoparticles and hydrogen peroxide in reactions similar to the Fenton and Haber–Weiss reactions. [ABSTRACT FROM AUTHOR]

The electrical and physical properties of MOS device structures (capacitor, field-effect transistor with an insulated gate and induced channel, CMOS integrated circuit) when exposed to unmodulated laser radiation are studied. The static and dynamic characteristics are measured. The theoretical study is carried out using the developed SPICE models and numerical experiments. An expression is obtained for the volt-ampere characteristics (VACs) of a field-effect transistor operating in a mode with constant optical illumination. It is shown that the characteristics of structures are determined by the generation and recombination of nonequilibrium charge carriers, the field effect, and the photovoltaic effect in p–n-junctions, the Dember effect, and the tunneling of charge carriers through the gate dielectric. The results of the study are of interest in terms of creating high-speed transistors and integrated circuits of a new type. [ABSTRACT FROM AUTHOR]

Physical processes occurring in air disperse media with solid particles in a laser channel during thermal emission of electrons from the particle surface and primary optical breakdown are considered. Changes in the refractive index during the formation of plasma halos around radiation-heated microparticles are estimated. A possibility of weak ionization of an air medium at a distance of several centimeters from the breakdown area due to the ionization of NO molecules and thermochemical reactions is shown. [ABSTRACT FROM AUTHOR]

Surface modifications for titanium, a material of choice for dental implants, can greatly alter the surface micro/nanotopography and composition of implants, leading to notable enhancements in their hydrophilicity, mechanical properties, osseointegration performance, and antibacterial performance, as well as their impacts on osteoblast activity and bone formation processes. This article aims to update titanium surface modification techniques for dental implants from the past to the present, along with their effects on osteoblasts and bone formation, by thoroughly summarizing findings from published studies. Peer-reviewed articles published in English consisting of in vitro, in vivo, and clinical studies on titanium dental implant surface treatments were searched in Google Scholar, PubMed/MEDLINE, ScienceDirect, and the Scopus databases from January 1983 to December 2023 and included in this review. The previous studies show that implant surface roughness, condition, and hydrophilicity are crucial for osteoblast adhesion and growth. While various techniques enhance osseointegration comparably, one of the most common approaches to accomplishing these properties is sandblasting large-grit acid etching surface treatment and coating with hydroxyapatite or chitosan. In conclusion, this review points out the efficacy of different subtraction and addition techniques in enhancing the surface properties of titanium dental implants, promoting favorable outcomes in terms of osteoblast activity and bone formation in various degrees. However, most existing studies predominantly compare treated and non-treated titanium, revealing a need for more comprehensive studies comparing the effects of various modification techniques. Moreover, further investigation of factors playing a role in the dynamic osseointegration process in addition to osteoblasts and their functions, as well as improved surface modification techniques for the treatment of compromised patients, is greatly required. [ABSTRACT FROM AUTHOR]

Photovoltaic conversion of laser radiation has found wide application in fiberoptic communication lines. Energy transfer via a laser beam is also relevant for remote power supply systems on Earth and in space. These systems can be used to power unmanned aerial vehicles, to transfer laser energy between spacecraft and from space solar panels to Earth. One of the main tasks in creating such systems is to ensure high efficiency of photovoltaic converters at high power (more than 100 W/cm2) of laser radiation. The article presents the results of research and development of photovoltaic converters of highpower laser radiation based on nanoheterostructures obtained by MOCVD epitaxy. The reduction of losses was achieved by embedding the “dielectric-silver” rear combined reflector into the structure. An increase in the generated voltage was achieved by shifting the volume charge region into the wide-gap layer of the p-GaAs-n-AlxGa1-xAs heterojunction. Thanks to an additional reduction in ohmic losses, efficiency values of 60 % have been achieved at laser radiation (λ = 860 nm) powers in the range of 50-400 W/cm2.

The effect of pulsed laser radiation on the change in the parameters of semiconductor structures of field-effect transistors with a Schottky gate with an operating frequency range of 1.5–8 GHz and integrated amplifiers with an operating frequency range of 0.4–6 GHz is studied. Laser radiation with 25 ns pulse duration, incident on the transistor crystal, creates a pulsed photo current. It is shown that the amplitude of the pulsed photo current is three times higher than the operating transistor current. The current-voltage characteristics of the field-effect transistor were measured in the mode of pulsed laser radiation. The amplitude dependence of the pulsed photocurrent in semiconductor structures on the power of laser radiation for various wavelengths of 1.06 and 0.53 μm is studied. It is shown that as a result of the action of pulsed laser radiation on semiconductor structures, a short disappearance of the amplification of the high-frequency signal at the amplifier output occurs. [ABSTRACT FROM AUTHOR]

The article considers the situation with uniformity assurance in measuring the output performance of high-power lasers, describing works that report an increase in the measured laser power of up to hundreds of kilowatts. The studies were carried out at the All-Russian Research Institute for Optical and Physical Measurements. In order to establish a system of metrological support for measuring the output performance of high-power continuous lasers, it was necessary to create three measurement standards, including GET 28-2022 State Primary Standard of the unit of average laser power, and four measuring instruments operating within the spectral range of 1.07–10.6 µm and the power range of 1–500 kW. A dynamic method for measuring high-power laser radiation was developed and used for the first time. This ensured the certification of instruments by means of standard radiation having a power of below 100 kW. The obtained results led to a significant increase in the level of metrological support to process and special high-power laser equipment. [ABSTRACT FROM AUTHOR]

The clean hydrogen is needed for green energy. It can be obtained by the water electrolysis, which is energetically unprofitable. The problem of hydrogen storage solution made it possible to use it as an automobile fuel. There was a place for the laser in the cramped fuel cell. Previously, it was proposed to introduce laser radiation with the wavelengths corresponding to the water molecule vibrational levels excitation into the reaction zone to increase energy efficiency. In addition, all processes on the Earth should be considered taking into account hydrogen degassing, that is, the hydrogen escape from the Earth into the atmosphere. And so the laser is the most suitable tool for finding places where the hydrogen exits to the surface. In this paper, it is proposed to use the Raman lidar for laser remote sensing of the hydrogen molecules during its leaks into the atmosphere. Based on the results of the Raman lidar equation computer simulation in the range of ranging distances up to 100 m, it is shown that its parameters optimization will reduce the values of detectable concentrations of the hydrogen molecules in the atmosphere. [ABSTRACT FROM AUTHOR]

It was experimentally found that speeds of hot submerged jets appearing in case of laser induced nucleation boiling of water near the tip of optical fiber submerged in water decrease exponentially with increasing laser power (heat flux). This result was obtained for a closed cylindrical cuvette where hot jets collided with walls and slipped the cuvette boundary transferring heat to it. The obtained result is to be taken into account in performing precise laser–induced surface cleaning inside confined volumes, in developing medical technologies for laser therapy of pathologically changed vessels or cysts, and in other applications. [ABSTRACT FROM AUTHOR]

The active Brownian motion of single dust particles in a three-dimensional DC discharge trap under the action of laser radiation is experimentally studied. Spherical particles of melamine formaldehyde (MF), part of the surface of which had a copper coating (Janus particle) are used in the experiment. Two-dimensional and three-dimensional analysis methods for root-mean-square displacements are compared. The mean kinetic energy of motion of dust particles at different laser irradiation intensities is determined. The energy balance of dust particles and the influence of their rotation on the nature of the motion are estimated. [ABSTRACT FROM AUTHOR]

The technology for production one and two-cascade power laser converters was presented in this paper. According to the measurement results of the grown samples, an efficiency of 34.5% was achieved. A promising design of a cascade photoelectric converter is proposed, in which the cascades are connected with using conduction channels based on GaP microcrystallites. [ABSTRACT FROM AUTHOR]

Microalga would be the paramount resource of biodiesel able of satisfying the world requirements for transportation fuels, which could fully replace the petrodiesel. Therefore, the research studies focus on developing novel biodiesel production methods. The present study investigates the effect of monochromatic light such as red light-emitting diodes (LEDs) and He–Ne red laser radiation on the accumulated lipid and the growth of the green microalgae Chlorella sorokiniana. The irradiation of microalgal cells with He–Ne red laser source which has a wavelength of 632.8 nm was hypothesized to enhance the accumulation of lipid inside the algal cells, which ultimately increases the biodiesel production. The photobiostimulating effects of laser irradiation on biodiesel was investigated by irradiating the microalga for a duration of 2 h with 632.8 nm He–Ne red laser source compared with 2 h irradiation with red LEDs and 2 h irradiation with white light (the control). The results showed that the oil content inside the algal cells irradiated with He–Ne red laser was 3.1 times the algal cells irradiated with white light (the control). Similarly, the biodiesel yielded from the algal cells irradiated with He–Ne red laser was 3.1 times the biodiesel yielded from the algal cells irradiated with white light (the control). However, the oil content and the biodiesel yield from algal cells irradiated with red LEDs were only 0.82 times those of the control. Therefore, it was concluded that the irradiation of microalga with red laser increases the biodiesel yield. [ABSTRACT FROM AUTHOR]

The acoustic properties of real liquids are largely related to the phase inclusions contained in them, of which gas bubbles are the most common. The aim of the work was to find the relationship between the nonlinear acoustic parameter and the cavitation strength of the liquid with the distribution of bubbles in the liquid, which has so far been poorly studied. The theoretical studies of the parameter of acoustic nonlinearity and the cavitation strength of a liquid with bubbles were carried out within the framework of the homogeneous approximation of a micro-homogeneous liquid; the relationship of these parameters with the bubble distribution function was established, and the typical values of these parameters for different concentrations of bubbles were calculated. Experimental measurements of the parameter of acoustic nonlinearity and the cavitation strength in the upper layer of seawater were carried out; these measurements were consistent with the theoretical estimates. A connection was established between the thresholds of acoustic and optical cavitation—the optical breakdown of a liquid by laser radiation. The results obtained can find practical application in the measurement of the cavitation strength of seawater at great depths in the sea, and the use of an optoacoustic method associated with the use of optical cavitation is proposed. [ABSTRACT FROM AUTHOR]

In this paper, a novel model based on the strain-temperature rate-dependent theory is investigated to study the coupling influences of thermal, elastic, and plasma waves during the photothermal process in a 2D axi-symmetric semiconducting half space. The surface absorption technique is used to illuminate the surface of the medium by a laser beam whose temporal and spatial profiles are Gaussian, moreover, the surface is also considered traction free. Integral transform method is applied using Laplace and Hankel transformations to obtain a general solution to the considered problem. Inverse Laplace transform is obtained computationally using Rimann-Sum approximation. Silicon element is chosen as an application to show the compatibility of the results of the MGL model with GL and CTE models, moreover the relaxation times effects of the new model were studied.

Subject and Purpose. Increasing the operational efficiency of laser generators and the amount of their radiated power is an important task in laser development, which can be approached to in a number of alternative ways. The present work has been aimed at increasing the efficiency of energy exchange between the active medium and the laser radiation by way of optimizing the radiated intensity distribution over the entire active volume within the resonant cavity of a novel structure. Methods and Methodology. A model for the process of radiated power amplification in the laser cavity has been considered. Losses within the cavity have been analyzed, as well as possibilities for improving the efficiency of energy transfer from the gain medium to the laser radiation. The importance of optimizing the density of laser radiation in the gain medium is substantiated, and the main problems that might arise clearly identified. The task of increasing the cross-section of the radiation beam being amplified in the active medium has been formulated, and a concept suggested for solving the problem through modification of the telescopic resonator’s optical scheme. Results. A novel configuration has been suggested for the laser resonator, where the radiated beam is expanded in width over two stages of counter propagation. Nonlinear regimes of increasing the beam cross-section in the resonator have been analyzed and recommendations formulated for selecting dimensions of the resonator and geometry of the mirrors, depending on the amount of amplification in the active material. Fragmentation of the output mirror is proposed as a means for feedback optimization, with account of diffraction-caused divergence of the radiation. As has been found, field-exciting elements can be placed inside the active medium. Recommendations are developed as for practical application of the scheme proposed in lasers of a variety of frequency ranges. Conclusions. Application of laser resonators of the design considered opens up new possibilities for increasing the efficiency of lasers and their radiated power.

Resonance interaction of a laser wave at twice the upper hybrid frequency with plasma in an inhomogeneous magnetic field is analyzed. A linear dependence of the magnetic field on the coordinate along the direction of propagation of the laser pulse and fulfillment of the resonance condition at the center of the plasma layer are assumed. It is demonstrated that the laser wave decays into two upper hybrid plasmons accompanied by excitation of the Bernstein modes under such an interaction. The occurance of an electromagnetic wave at the upper hybrid frequency reflected from the plasma boundary is detected. The conclusion is drawn that the reflected wave is driven upon interaction of the Bernstein modes with the upper hybrid plasmons since the wave disappears in the case of a cold-plasma layer. The dependence of average energy gained by electrons upon development of instability on the gradient of the external magnetic field is investigated. [ABSTRACT FROM AUTHOR]

Laser technologies for processing metals used as heat exchange surfaces are unrivaled to solve a number of problems in the energy industry. This is explained by the fact that after laser radiation treatment, metal surfaces gain unique surface functional properties (extreme wettability properties, high resistance to corrosion in contact with traditional coolants, high abrasive and cavitation resistance). The study of the processes of evaporation, boiling, and condensation on such surfaces is hampered by one of the unsolved problems, which is the lack of the ability to predict the configuration of microtextures, for example, in the form of micropillars and microchannels with predetermined sizes. In this work, a graphic–analytical technique based on the use of ablation spot sizes for the formation of a given configuration and microtexture dimensions on traditional structural materials of heat exchange surfaces is developed. Based on experimental data, regime maps were constructed for the formation of microtextures on the surfaces of aluminum alloy AlMg6 and steel AISI 310. The prospects for using metal surfaces with a given microtexture formed by laser radiation to intensify the phase transition of coolants and control convective flows in a droplet lying on a heated surface were assessed. The obtained results can be used in the development of spray (drip) irrigation systems to provide thermal protection for heat-stressed equipment. [ABSTRACT FROM AUTHOR]

The influence of an electric field on the plasma of an optical discharge in subsonic and supersonic air flows has been studied experimentally. The presence of a weak electric field practically does not affect the size of the plasma formation, but, regardless of the configuration of the field lines and the polarity of the applied voltage, it leads to a decrease in the probability of optical breakdown. The experiment has shown that the plasma created by focused laser radiation is very sensitive to the presence of an electric field. When a voltage exceeding 22 kV was applied to the ring electrodes, powerful quasi-stationary streamers were formed in the flow. The presence of an optical discharge plasma made it possible to create an electric discharge in fields with an intensity below the breakdown threshold of the medium. The effect of quenching and the processes of development of an optical discharge were studied depending on the speed and characteristics of the electric field. Quenching of the optical discharge was observed when a voltage of 22 kV and higher was applied. Despite the preservation of the geometric dimensions of the optical discharge, the high-temperature region in the flow can be increased by using electric streamers. This leads to an increase in the energy supplied to the flow, and thus allows combustion to be initiated and flame stabilized at higher flow rates. [ABSTRACT FROM AUTHOR]

A model of an autonomous receiving station of free space optical communication system based on a multi-section energy heterostructure (HJT) Si photoconverter and an information photodetector based on AlGaAs/GaAs p–i–n photodiodes has been developed. The energy part, when excited by laser radiation with a power of ~264 W at a wavelength of 0.974 μm in the photovoltaic mode, provided ≥60 W of electric power. The photodetector of the information channel, when excited by pulsed radiation at a wavelength of 0.78 μm, provides response time in the photovoltaic mode in the sub-nanosecond range. [ABSTRACT FROM AUTHOR]

Using an analytical description of the evolution of harmonic power in free-electron laser (FEL) undulators, the influence of electron beam parameters on the fundamental characteristics of FEL radiation is investigated: gain length, spectrum, and harmonic power. The possibility of suppressing even harmonics in the FEL as a light source for material and surface studies using second harmonic generation (SHG) nonlinear response analysis is explored. The main factors affecting the emission of even harmonics in FELs are identified; the influence of the beam cross-section and the spread of electron energies on their radiation is analyzed. The example of the FEL LEUTL with visible light emission, which is used in the studies of optical properties of materials and the chemical state of molecules on surfaces and at interfaces, is considered. In this context, the possibility of suppressing the second harmonic in FELs is analyzed. [ABSTRACT FROM AUTHOR]

The objective of the research was to analyze by Raman spectroscopy the morphology of gold nanoparticles generated by laser ablation in L-Cysteine of purity = 97% dissolved in ultrapure water for the detection by color change of mercury dissolved in water. Three samples of 10 ml of ultrapure water were prepared with aggregation of 10 ul of L-Cysteine with concentrations of 1, 10 and 20 mM; the generation of the gold nanoparticles was by laser ablation with a wavelength ? = 1064 nm, energy of 60.28 mJ/p located at 30 cm from the convex lens generating ablation at 10 cm on a gold plate of dimensions 10×15 mm with thickness of 1 mm, for 30 min. The gold nanoparticles generated in these aqueous environments were characterized by Raman spectroscopy using a laser with a sensitivity of 785 nm with Raman Shift analysis range 860-3200 cm-1 and controlled power at 499 mW. The nanoparticles presented maximum peak resonance around Raman Shift 1164.96 cm-1 and 1288.06 cm-1. With the AuNPs + L-Cysteine sample with concentration of 10 mM, the author proceeded to the detection of Hg2+ prepared in 20 µl of ultrapure water at concentrations of 0.1, 5 and 10 µM; when adding 100 µl of AuNPs + L-Cysteine two peak absorbance spectra were obtained with different amplitudes observed by UV-Vis spectroscopy, indicating that Hg2+ decreased the repulsion of the negatively charged AuNPs, generating the visible color change for the three concentrations of Hg2+ with 25 minutes of agitation, turning intense purple for 10 µM of Hg2+; enabling the detection of mercury in water. [ABSTRACT FROM AUTHOR]

We describe an approach to detecting off-axis radiation of laser beams propagating in scattering media, especially in the atmosphere, in the presence of background (solar) radiation. The method relies on a generalization of the conventional intensity interferometry (II) theory to scenarios involving coexisting sources of relatively long (laser radiation) and much shorter (background) coherence times. In such circumstances, the high coherence of the laser light allows its discrimination against even much stronger, but low-coherence, background. We propose a simple detection system consisting of a small array of photodetectors (e.g. photodiodes) and estimate the ratio of the background-to-laser irradiances at which the laser radiation is expected to be detectable. [ABSTRACT FROM AUTHOR]

The possibility of active laser delivery of a modern chlorine-containing photosensitizing drug Chloderm (Chloderm, Russia) under the nail plate by laser radiation with a wavelength of 450 nm for the purpose of photodynamic therapy of onychomycosis is studied. In an in vitro experiment, sequential laser microporation of the nail plate and active delivery of the drug under the nail plate by this laser radiation with an intensity of up to 200 W/cm2 were investigated. The results of studying the absorption spectra of an aqueous solution of Chloderm in the range of 400–900 nm before and after exposure to 450 nm laser radiation are presented. It is demonstrated that sequential laser microporation and active laser drug delivery under the nail plate is possible at laser radiation intensity greater than 178 W/cm2. It is shown that the maximum rate and efficiency of nail plate ablation by 450 nm laser radiation is achieved at an intensity of 200 W/cm2 and is 2750 ± 30 μm/s and 1.47 ± 0.05 μm/mJ, respectively. The delivery rate of Chloderm under the nail plate is 1.15 ± 0.1 mg/s. It is shown that exposure to 450 nm laser radiation at the intensity of 200 W/cm2 for a time sufficient to deliver the drug under the nail plate does not change the extinction coefficient of the drug at the laser wavelength and slightly changes the conformational state of Chloderm. [ABSTRACT FROM AUTHOR]

In this study, the dyeing properties of a natural dye extracted from the kermes insect on silk were examined. Insect dye at different concentration rates of 5%, 10%, and 15% wt was applied to silk fabrics mordanted with alum [KAl(SO4)2.12H2O] and iron-(II) sulfate [FeSO4.7H2O]. Then, the Nd:YAG laser device was used to investigate the laser radiation effects on the color of the fabric. The dyed fabrics were analyzed by different analytical and technical methods. The RP-HPLC-DAD method was used for the identification of the coloring compounds of fabrics dyed with kermes. The color coordinates and fastness values of rubbing, washing, and light were investigated. Overall, the fastness results were excellent. SEM-EDX was performed for morphological examinations and CIEL*a*b* color values were measured for colorimetric examinations after laser radiation. [ABSTRACT FROM AUTHOR]

The laser initiation threshold energy densities (the laser sensitivity) of pentaerythritol tetranitrate (PETN) containing a nanostructured zinc oxide powder doped with silver (ZnO:Ag) are studied in the article. The second harmonic radiation of a pulsed Nd:YAG laser with a wavelength of 532 nm and a CW laser diode with a wavelength of 450 nm are used for initiation. The ZnO:Ag nanopowder can potentially provide photoinitiation of PETN by the photochemical mechanism. The initiation thresholds via pulsed laser initiation are compared with compositions of PETN and gold nanoparticles, which have similar optical characteristics but are chemically inert. The absorption spectra of materials in the UV, visible, and near-IR spectral regions are studied. The threshold of the laser initiation of the explosion of the PETN–ZnO:Ag composite by pulsed radiation is lower than one-third of the threshold of initiation of the PETN-nanogold composite, which has similar values of optical density. The addition of 1% mass of ZnO:Ag for the first time makes it possible to initiate PETN reliably (without failures) by the radiation of a low-power visible laser diode. The results and their comparison with the published data allow us to make a reasonable assumption on the contribution of the photochemical stages to the laser initiation of the PETN–ZnO:Ag composite by visible laser radiation. [ABSTRACT FROM AUTHOR]

The article discusses the evolution of the endovenous laser ablation technique for the treatment of varicose vein disease of lower extremities. The history of studies aimed at improving the endovenous laser ablation is provided. The authors described the features of endovenous laser ablation with wavelengths from λ = 0.445 to 1.94 µm, alongside with edge- and radial-emitting working fibers, as well as fibers with radiation absorption at its distal end. The physical and biophysical mechanisms of the most popular to-date method for outpatient treatment of varicose vein disease of lower extremities are reviewed. The propagation process of laser radiation in the scattering medium is described, and the important role of the radiation scattering effect on the depth of its penetration into biological tissues is shown. The processes that take place during endovenous laser ablation are considered. The difference in physical processes that take place during the use of laser radiation mainly absorbed by hemoglobin (hemoglobin-absorbed range) and by water (water-absorbed range) is described. Expedience of simulating the processes that take place during endovenous laser ablation with the use of blood plasma has been substantiated. The blood plasma simulation demonstrated the decisive action of laser-induced boiling on thermal damage to the vein wall, which causes its fibrous transformation. It has been shown that the use of radial-emitting fibres during intense boiling generates steam bubbles around the site of radiation coupling. The contents of such steam bubbles do not absorb radiation, which thus reaches the venous wall, causing its symmetrical thermal damage. The advantages of using water-absorbing radiation with a wavelength of λ = 1.94 µm in conjunction with a radial-emitting fibre have been substantiated.

It has been shown that defect-free Stone–Wales (SW) free few-layer graphene (FLG) can be obtained by carbonizing lignin under conditions of self-propagating high-temperature synthesis (SHS). The obtained few-layer graphene was used as a modifying additive for pyrotechnic compositions. It was found that the addition of 2.5 mass % of few-layer graphene synthesized from lignin to a pyrotechnic complex based on porous silicon and fluoropolymer leads to a significant increase in the combustion intensity of pyrotechnic compositions.

Surface modifications for titanium, a material of choice for dental implants, can greatly alter the surface micro/nanotopography and composition of implants, leading to notable enhancements in their hydrophilicity, mechanical properties, osseointegration performance, and antibacterial performance, as well as their impacts on osteoblast activity and bone formation processes. This article aims to update titanium surface modification techniques for dental implants from the past to the present, along with their effects on osteoblasts and bone formation, by thoroughly summarizing findings from published studies. Peer-reviewed articles published in English consisting of in vitro, in vivo, and clinical studies on titanium dental implant surface treatments were searched in Google Scholar, PubMed/MEDLINE, ScienceDirect, and the Scopus databases from January 1983 to December 2023 and included in this review. The previous studies show that implant surface roughness, condition, and hydrophilicity are crucial for osteoblast adhesion and growth. While various techniques enhance osseointegration comparably, one of the most common approaches to accomplishing these properties is sandblasting large-grit acid etching surface treatment and coating with hydroxyapatite or chitosan. In conclusion, this review points out the efficacy of different subtraction and addition techniques in enhancing the surface properties of titanium dental implants, promoting favorable outcomes in terms of osteoblast activity and bone formation in various degrees. However, most existing studies predominantly compare treated and non-treated titanium, revealing a need for more comprehensive studies comparing the effects of various modification techniques. Moreover, further investigation of factors playing a role in the dynamic osseointegration process in addition to osteoblasts and their functions, as well as improved surface modification techniques for the treatment of compromised patients, is greatly required.

The spectral-kinetic characteristics of the glow of brown-coal samples exposed to laser pulses (1064 nm, 14 ns, 1 GW/cm2) in air at atmospheric pressure and in vacuum at a pressure of 10−2 Torr were studied. A vapor plasma torch was observed over the samples in a vacuum during the action of the laser pulses. Glow lines of ionized carbon and hydrogen atoms were identified. The CO flame glow dominated the spectra at atmospheric pressure. The rotational-vibrational glow of H2O and the thermal glow of carbon particles were distinguished in the spectra after exposure to the laser. The nonvolatile residue of coal particles combusted with escape of incandescent carbon particles at a temperature of ~2500 K in air at atmospheric pressure in the time interval 0.2–1.0 ms with exposure to laser pulses of W = 1 GW/cm2. [ABSTRACT FROM AUTHOR]

A study has been made of the process of heating of an inhomogeneous solid body by laser radiation, that is described by a one-dimensional parabolic equation with a volume heat source. The inverse problem of determining the law of variation in the density of laser-radiation power with the depth of the solid body has been posed. The temperature distribution through the body′s depth at a certain fixed instant of time was used as the supplementary condition. A discrete analog of the posed problem has been constructed with finite-difference approximations. To solve the obtained difference problem, a special representation was proposed which allows splitting this problem into two mutually independent difference problems. As a result, an explicit formula has been obtained from which the law of variation in the density of laser-radiation power with the depth of the solid body is restored. [ABSTRACT FROM AUTHOR]

This study uses a serial information transmission scheme to discuss the issues faced in transmitting unit average power of laser radiation from a reference converter of the corresponding standard to a control measuring converter. A large difference in the time constants of these converters leads to increased measurement error. To reduce this error, herein, an algorithm is proposed based on averaging the results of multiple measurements while determining the main transmission parameter of unit average power (calibration coefficient). The statistical characteristics of the estimation of the calibration coefficient are analyzed herein. In the model based on measuring transducers having lumped parameters of the first order, relationships that characterize the influence of a correlated stationary-fluctuation component related to the instability in laser radiation power are obtained to determine the calibration coefficient while averaging the results of multiple measurements. In this case, the median of the distribution of its estimate should be used as the calibration coefficient because the median is unbiased and consistent. Equations are obtained to determine the error in estimating the calibration coefficient, and dependencies are presented that enable setting the required measurement averaging time and number of readings of the measured signals. Using the proposed algorithm improves the metrological characteristics of GET 28-2016, the state primary standard of the unit of average laser radiation. [ABSTRACT FROM AUTHOR]

The process of laser formation of microholes in semiconductor substrates using an EM-4452-1 laser-processing unit with a pulse repetition frequency of a picosecond laser from 10 to 300 kHz at a radiation energy up to 10 μJ is investigated. The combination of high-speed movements of the laser beam by the galvanoscanner system and precise positioning of the processed material increases the efficiency of laser microprocessing and expands the functional capabilities of the equipment. [ABSTRACT FROM AUTHOR]

Natural zeolite is a widely used material with excellent environmental cleaning performance, especially in water and wastewater treatment. Natural zeolite (Zini) calcined by CO2-laser radiation (ZL) was tested as a catalyst for the photodegradation and the adsorption of industrial azo dye Lanasol Yellow 4G (LY4G) in water. Morphology, chemical structure, and surface composition of Zini and ZL were analyzed by XRD, SEM, EDS, and XPS. UV/Visible spectrophotometry was used to evaluate the photocatalytic activity of Zini and ZL. The photocatalytic activity of the studied zeolites was associated with the presence of Fe oxides in their composition. Laser-treated natural zeolite showed higher efficiency as a photocatalyst compared to untreated natural zeolite. [ABSTRACT FROM AUTHOR]

The paper describes the metrological assurance of uniformity in measuring the parameters of high-intensity laser radiation for technological and special equipment. A laser power stabilization system with an output power of 2–1·104 W has been developed and studied. The presented stabilization system reduces the error in transferring the unit of average laser power when using an industrial laser having unstable output power as part of a measurement standard. GET 28-2022 National Primary Standard for the unit of average laser power was approved; this standard includes a power-stabilized laser, as well as a standard thermoelectric measuring transducer and a measuring beam splitter. The authors studied the means of transferring the unit of average laser power from the range of 1·10–9–2 W to the range of 2–1·104 W, as well as a system for reproducing and transferring the average power unit within the range of 2–1·104 W. With the use of the developed industrial laser stabilization system, the laser power of the standard increased from 2 to 1·104 W. Within the laser power range provided by GET 28-2022, the total standard uncertainty in reproducing and transferring the unit of average laser power does not exceed 0.636%. GET 28-2022 can be used to provide metrological support for laser systems designed for various applications operating within the laser power range of 2–1·104 W, specifically systems intended for laser hardening, cutting, welding, etc. [ABSTRACT FROM AUTHOR]

A methodology, technique, and research results for the synthesis of films on a glass surface upon irradiation of aqueous solutions of copper sulfate with laser radiation are presented. The studies used the radiation of a yttrium-aluminum garnet laser, its second harmonic and the radiation of a semiconductor laser. Solutions with different concentrations of copper sulfate were used. The structure and and characteristics of the control films obtained as a result of drying solutions without exposure to laser radiation. Films synthesized under the action of laser optical characteristics of the films obtained in this case are compared with the structure radiation have both ordered and disordered structures. The characteristic dimensions of the structural elements of these films are 0.5-2 microns. For solutions with low concentrations, the density of the coating of glass substrates with films obtained under the action of laser radiation is much higher than the density of the coating with control films. The transmissions of the films were studied in the spectral range 300-1200 nm. It was found that the transmission of films obtained under the action of laser radiation and control films differ. [ABSTRACT FROM AUTHOR]

The paper investigates the physicochemical processes that occur during laser-induced breakdown in colloids of gadolinium oxide nanoparticles of different concentrations. A monotonic change in the number of optical breakdowns, the average distance between the nearest breakdowns in the track of a single laser pulse, the average plasma size of a single optical breakdown, the integral luminosity of an optical breakdown plasma flash, the intensity of acoustic signals, and the rate of formation of dissociation products—O2, H2, OH•, and H2O2—is demonstrated. It is shown that the rate of formation of chemical products of the decomposition of H2O molecules under the action of breakdown when using nanoparticles of rare earth metals, in particular, gadolinium oxide, is the highest compared to other materials. Based on one laser pulse, the rates of formation of chemical products formed during the dissociation of water during laser-induced breakdown of a colloid of gadolinium oxide nanoparticles are 13.13 nmol/pulse for H2, 5.41 nmol/pulse for O2, and 6.98 nmol/pulse for hydrogen peroxide. [ABSTRACT FROM AUTHOR]