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Alloy 400 is a corrosion-resistant, NiCu-based material which is used in numerous industrial applications, especially in marine environments and the high-temperature chemical industry. As conventional manufacturing limits geometrical complexity, additive manufacturing (AM) of the present alloy system promises great potential. For this purpose, a robust process chain, consisting of powder production via gas atomization and a design of experiment (DoE) approach for laser powder bed fusion (LPBF), was developed. With a narrow particle size distribution, powders were found to be spherical, flowable, consistent in chemical composition, and, hence, generally applicable to the LPBF process. Copper segregations at grain boundaries were clearly detected in powders. For printed parts instead, low-intensity micro-segregations at cell walls were discovered, being correlated with the iterative thermal stress applied to solidified melt-pool-near grains during layer-by-layer manufacturing. For the production of nearly defect-free LPBF structures, DoE suggested a single optimum parameter set instead of a broad energy density range. The latter key figure was found to be misleading in terms of part densities, making it an outdated tool in modern, software-based process parameter optimization. On the microscale, printed parts showed an orientation of melt pools along the build direction with a slight crystallographic [101] texture. Micro-dendritic structures were detected on the nanoscale being intersected by a high number of dislocations. Checked against hot-extruded reference material, the LPBF variant performed better in terms of strength while lacking in ductility, being attributed to a finer grain structure and residual porosity, respectively. [ABSTRACT FROM AUTHOR]

Prospects for the application of orbital lidars for the detection of gas leaks from spacecrafts are investigated. The optical characteristics of the main light-scattering components – molecules and atoms of gases, are estimated at altitudes of 100–600 km from the Earth surface. It is shown that an orbital lidar with modern technical parameters can reliably detect signals from dispersed gas leak components at distances from several tens to one hundred meters from the spacecraft. [ABSTRACT FROM AUTHOR]

In diffusion-cooled gas lasers, the laser medium gas is cooled through the discharge tube wall. Empirical findings suggest that, in longitudinally excited CO2 lasers with fast pulsed discharges, the materials of the discharge tube and coolant impact the discharge. This study investigates their effects on fast discharges rather than on cooling. Within a discharge tube with a cooling tube, the discharge tube and coolant create a capacitor, influencing the discharge. The laser output energy varies based on the discharge tube and coolant materials. The primary discharge input energy is influenced by these materials, as is the efficiency of converting it into laser output energy. [ABSTRACT FROM AUTHOR]

Mass diffusion coefficient measurement techniques with high temporal and spatial resolution have become essential for the research and development of leading-edge technology in a wide range of cross-disciplinary fields, but cannot be achieved using conventional methods. We provide a comprehensive review of the state-of-the-art theoretical and experimental investigations on Soret forced Rayleigh scattering (SFRS), a grating excitation technique (GET) for measuring the mass diffusion coefficient of binary liquid mixtures. SFRS utilizes the Soret effect to create micrometer-order periodic spatial concentration modulation in a sample due to the absorption of an optical interference grating generated by two intersecting heating laser beams. The decay of the concentration modulation by the mass diffusion process within several milliseconds is detected by the diffraction of a probing beam. The theoretical considerations regarding deviations from the ideal mass diffusion conditions are the effects of: (1) the Gaussian beam intensity distribution, (2) the light absorbing material and (3) the cell wall. The proper settings for the optical system are also analyzed, e.g., the effect of coherency and polarization of the heating laser and the effect of the z-direction length of the interference region. We also consider the frame of reference, center of gravity invariance and effect of convection, which are particularly important for mass diffusion experiments. Using the correct implementation of the theory, the optimal SFRS apparatus design and its appropriate use are described in detail. Finally, two successful applications of SFRS are demonstrated using visible light laser heating and mid-wavelength infrared gas laser heating. [ABSTRACT FROM AUTHOR]

This study utilizes polishing abrasives containing TiO2 particles to simulate the wear process of small holes during spinning and analyzes the internal structure of worn small holes. It investigates the wear characteristics of 316L stainless steel spinneret plates processed by electrical discharge machining and laser drilling. Abrasive tests were performed on spinneret holes obtained by these processes using abrasives with different TiO2 particle concentrations. The results show that TiO2 particles in the abrasive induce wear on the inner wall of spinneret holes. Holes processed with TiO2-containing abrasives exhibit noticeable morphological changes on the wall surface compared to those without TiO2 particles. The degree of wear increases with TiO2 concentration. Additionally, holes processed by electrical discharge machining exhibit significantly higher wear than those processed by laser drilling under the same concentration conditions, indicating the significant impact of spinneret hole processing methods on wear resistance performance. [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]

Laser corneal reshaping is an eye surgery utilizes UV lasers to modify a targeted corneal surface to correct vision disorders such as myopia, hyperopia and astigmatism. The most commonly used laser type in such treatment is a pulsed gas laser namely argon fluoride (ArF) excimer laser (193 nm). A mixture of Argon, Fluorine and high percentage of Neon gas is utilized for producing the required laser. However, the availability of Neon gas is currently very limited due to the existent Russian-Ukraine war as this region is considered the main supplier of pure Neon gas. The present work provides a novel alternative system for the commercially available corneal reshaping eye surgery devices with a special opening for entering the operational laser beam from external sources. The proposed system is a flying spot platform coupled with a solid state laser, that is a forth harmonic of Nd: YAG laser. The aperture in the system's design enables it to take in the generated UV-laser beam (266 nm) from the external Nd: YAG laser source. The beam is then modified and directed at the treatment area. The device was tested for hyperopia laser profile algorithm on different targets. Furthermore, the hyperopia profile procedure was also applied to the ex-vivo rabbit eye to investigate the ablation effect on the corneal tissues. The obtained results showed an appropriate ablation effect for hyperopic correction via a complete corneal reshaping platform. Although, the device's current state may not be appropriate for immediate clinical use. It holds significant value as a training and educational platform. [ABSTRACT FROM AUTHOR]

A short external cavity (EC) providing a single frequency lasing of quantum-well diode lasers with broad optical gain profiles has been developed. A feature of the proposed EC is the use of a resonant reflector formed by two thin (with thickness of approximately 100 µm) cover glasses as a return mirror. The HL8338MG laser equipped with a similar short EC made it possible to demonstrate the continuous optical frequency tuning within 100 GHz and discrete wavelength tuning in the 12.3 nm range with an output power of approximately 20 mW. The applicability of such a tunable diode laser source for gas spectroscopy was confirmed by the observation of three krypton absorption lines near 829 nm in a low-pressure radio frequency discharge. [ABSTRACT FROM AUTHOR]

In the field of ultra-thick plate cutting, thermal cutting using high-temperature heat is used rather than mechanical cutting, and research is being conducted to increase the efficiency of cutting. In this paper, in order to improve cutting efficiency, a hybrid cutting head using both laser and gas cutting was designed, and the optimal cutting conditions were demonstrated through an experiment for cutting ultra-thick plate using the manufactured cutting head. The plate material used 100 t carbon steel, and a multi-axis hybrid method was adopted. As a result of the experiment was confirmed that the cutting speed was improved more than twice as much as when using the single cutting method, and the optimal speed condition in which sludge did not occur was derived. The maximum cutting speed was 600 mm/min, and the optimal cutting speed at which sludge did not occur was confirmed at 550 mm/min. [ABSTRACT FROM AUTHOR]

In a previous study, we considered that the laser characteristics of longitudinal discharge pumped CO2 lasers with fast pulse discharge were affected by changes in the discharge characteristics due to operations with high repetition rates. However, the discharge form has not been investigated in detail. In this study, the effects of repetition rate and gas pressure on the discharge were investigated by observing the discharge using a Pyrex discharge tube with an inner diameter of 12.6 mm and, length of 470 mm, and a CO2/N2/He gas mixture ratio of 1:1:2. At repetition rates of 150 Hz or lower, the discharge was uniform throughout the inner diameter of the discharge tube, whereas at repetition rates of 200 Hz or higher, the discharge contracted. The contracted discharge is thought to be caused by the residual charged particles generated by the discharge. At a high repetition rate, the discharge current density changes owing to the contraction of the discharge, which affects the optimal gas pressure and laser output energy. These findings are important for establishing the optimal operating conditions for longitudinally excited CO2 lasers pumped by fast pulsed discharges. [ABSTRACT FROM AUTHOR]

The article considers the results of studying the emission radiation of Ar, Kr, CO2, CHF3, CF4 and N2 gas jets excited by pulsed laser radiation. The shape of the spectral dependence in the spectral range 2.3‒4.4 nm and the emission intensity of a number of lines in absolute units were studied. To excite the targets, a Nd:YAG laser, λ = 1064 nm, τ = 5.2 ns, Eimp= 0.8 J was used. A supersonic conical nozzle with dcr = 450 μm, 2α = 11°, L = 5 mm was used to form a pulsed gas jet. The pressure at the nozzle inlet was 25 bar, which corresponds to the developed condensation of molecular gases in gas jets. The spectra were deciphered and the ions emitting under the given experimental conditions were determined. [ABSTRACT FROM AUTHOR]

A theoretical analysis of a radiation amplifier based on metastable noble gas atoms excited by laser diodes in transverse pumping mode is presented. In the case when the amplified radiation reaches a sufficiently high intensity, the original equations allow a simple analytical solution, from which all the most important characteristics of the amplifier and the optimal parameters of both the working environment and the pump radiation, which ensure the most efficient operation of the amplifier, are easily found. [ABSTRACT FROM AUTHOR]

The possibilities of organizing a repetitively pulsed process with given frequency characteristics in a cavity of constant volume with an external energy supply to the working gas mixture are considered. Modelling of gas-dynamic and thermal processes is carried out using the numerical solution of the conjugate heat transfer problem. The gas medium is described on the basis of a viscous compressible gas model. To find the temperature field in the walls of the structure, the equation of non-stationary heat conduction is solved. The conjugation of temperature fields in a gas and a solid is carried out using an iterative procedure. In the calculations, the geometrical parameters of the cavity, the density of the energy supply, the initial pressure, and the composition of the working mixture are varied. The results of calculations obtained in the framework of the one-dimensional and two-dimensional formulation of the problem under the action of both a single pulse and a series of pulses are compared. The results obtained demonstrate the possibility of implementing the required frequency characteristics of the process for given geometric and energy parameters. [ABSTRACT FROM AUTHOR]

The findings of the study demonstrate the impact of low-intensity laser and quasi-monochromatic light on the biosynthetic activity of the edible medicinal fungus L. edodes during submerged cultivation. An artificial lighting installation based on matrices of light-emitting diodes (LED) emitting light at 470 nm (blue), 530 nm (green), 650 nm (red), and argon gas laser (488 nm) was used. Irradiation with blue and red LED and laser led to a shortening of the lag phase by 2 days and an increase in the mycelial mass. Irradiation with laser light resulted in the highest mycelial mass yield (14.1 g/L) on the 8th day of cultivation. Irradiation in all used wavelength ranges caused an increase in the synthesis of both extracellular and intracellular polysaccharides. Laser light at 488 nm and LED at 470 nm proved to be the most effective. Irradiation with red, green, and blue laser light caused an increase in the total amount of fatty acids in the mycelial mass compared to the control. A significant distinction in qualitative composition was observed: short-chain acids C6‒C12 compounds were produced under red light irradiation, whereas long-chain C20‒C24 were formed under green light irradiation. The most significant changes in the aromatic profile of the mycelial mass and culture liquid were recorded upon irradiation with green light. The content of aromatic components increased 24.6 times in the mycelial mass and 38.5 times in the culture liquid. The results suggest the possibility of using low-intensity quasi-monochromatic light for targeted regulation of L. edodes biosynthetic activity. [ABSTRACT FROM AUTHOR]

The gain characteristics of a CO2 laser pumped by a longitudinal pulsed discharge were investigated to develop a compact He-free CO2 laser operating at a high repetition rate. The longitudinal discharge tube had an inner diameter of 0.8 cm and a length of 45 cm. High-voltage pulses with a discharge starting voltage of 13.4–30.2 kV at a rise time of about 321 ns were applied to the discharge tube. CO2/N2 mixture gas with mixing ratios of 1:0, 1:1, 1:2 and 1:3 was used. The small signal gain coefficient was measured by inputting a seed CO2 laser pulse into the longitudinal discharge tube. The small signal gain coefficient depended on the delay time between the start of the discharge in the longitudinal discharge tube and the input of a seed CO2 laser pulse, the gas mixing ratio, the gas pressure, the repetition rate and the input energy to the longitudinal discharge tube. In this work, in He-free gas, the maximum small signal gain coefficient at a repetition rate of 300 Hz was 2.11%/cm with a delay time of 30.4 μs, a CO2/N2 gas mixing ratio of 1:2, a gas pressure of 2.6 kPa and an input energy of 191 mJ. [ABSTRACT FROM AUTHOR]

To solve such global problems as climate stabilization and reducing greenhouse gas luminescences requires an integrated approach, including a strategic analysis of the problem and the development of criteria for selecting proposed solutions, a natural scientific research on the possibilities and ways to implement the assigned tasks, as well as an economic justification for the feasibility of implementing the developed measures. The present publication is an attempt to apply this approach to the problem of hydrogen energy via proposing the production of hydrogen by pyrolysis of natural gas in laser plasma as one of the ways to its solution. Therewith, the main attention is focused on the chemical processes that occur in laser plasma, as well as on the nature of the transformations that occur in the solid pyrolysis product. [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 influence of post-welding heat treatment on the surface and corrosion properties of the interstitial high-entropy alloy (Fe50Mn30Cr10Co10)99C1 has been examined using gas tungsten arc welding (GTAW) and laser welding. The as-welded and post-weld heat-treated samples were characterized using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Face-centered cubic (FCC) and hexagonal close-packed (HCP) structures were present in the base metal. There was no change in the phases after welding and post-heat treatment. After laser and GTAW, a small reduction in hardness (25 HV) was noticed. Following both laser and GTAW processes, the base metal's corrosion resistance dropped. However, heat treatment applied after the weld brought the resistance back to almost base metal levels (0.002 mm/year). The development of Mn oxides on the surface, which minimizes the micro-segregation of Cr and generates a uniform Cr oxides layer, is primarily responsible for the increased corrosion resistance in the post-welded samples. This layer also exhibits superior passivation and corrosion resistance. The study clearly demonstrates that, in Mn-containing high-entropy alloys, it is important to suppress elemental Mn content on the surface for improved corrosion resistance. [ABSTRACT FROM AUTHOR]

In a short-pulse CO2 laser based on discharge excitation, there is a pulse tail that depends on the device configuration and operating conditions. The pulse tail is longer than the spike pulse and causes thermal effects such as a crack, heat-affected zones (HAZ), and so on. There are various types of glass having different physical constants related to heat, such as the thermal expansion coefficient and the softening point. Even if the same CO2 laser pulse is radiated onto glass, the processing results may differ depending on the glass material. Four types of glass, namely, crown glass, soda-lime glass, borosilicate glass, and synthetic quartz glass were irradiated with two types of short CO2 laser pulses, one with a large pulse tail and one with a small pulse tail, at a repetition rate of 200 Hz and a fluence per pulse of 22 J/cm2. As the processing characteristics, the ratios of the surface hole diameter and the HAZ diameter to the irradiation diameter, as well as the drilling depth, were investigated. The pulse-tail energy of the short CO2 laser pulses did not affect the surface hole diameter. In the glasses with small softening points of 740 °C or less, the pulse-tail energy of short CO2 laser pulses affected the HAZ with a large number of pulse irradiations with a total irradiation fluence of 2000 J/cm2 or more. The short CO2 laser pulses with a small tail produced a smaller HAZ than the short CO2 laser pulses with a large tail. In drilling with a large number of pulse irradiations, the short CO2 laser pulses with a small tail produced deeper drilling than the short CO2 laser pulses with a large tail. The glass material did not affect the surface hole diameter and the drilling depth. The glass material affected the HAZ. [ABSTRACT FROM AUTHOR]

Purpose: Laser endoscopic enucleation of the prostate (EEP) for benign prostatic obstruction has become increasingly prevalent worldwide. Considering the medical cost-savings and concomitantly fewer nosocomial infections, the feasibility of same-day postoperative discharge of patients who have undergone laser EEP in terms of its safety and effectiveness has become a subject matter of growing interest. We aimed to review those studies focussing on day-case surgery (DCS) in patients undergoing laser EEP. Methods: A systematic search was conducted using PubMed-MEDLINE and Web of Science databases until October 2022 with the following search terms: "same day discharge AND laser enucleation of the prostate", "day-case AND laser enucleation of the prostate", "same day surgery AND laser enucleation of the prostate" and "one day surgery AND laser enucleation of the prostate" by combining PICO (population, intervention, comparison, outcome) terms. We identified 15 eligible studies. Results: While 14 of the studies focussed on holmium laser EEP, one focused on thulium laser vapoenucleation of the prostate. We observed an improvement in functional parameters in all studies we reviewed, and DCS success and readmission rates ranged between 35.3–100% and 0–17.8%, respectively. The complication rates varied between 0 and 36.7%, most of the complicatons were Clavien-Dindo (CD) I and II. CD ≥ III complications did not significantly differ between same day discharge (SDD) and non-SDD groups in the studies. Conclusion: Laser EEP is feasible and promising DCS treatment option delivering improved functional parameters compared to baseline values, and lower perioperative complication and readmission rates in certain patients. [ABSTRACT FROM AUTHOR]

An efficient pulsed gas-discharge inductive CO2-laser with a radiation energy of 1.05 J has been developed for the first time. In this case, the pulse duration of the laser radiation was about 10 ms. The maximum efficiency of 21.1% was obtained at a radiation energy of 340 mJ. HF current pulses propagated along the inductor conductor and, thus, an inductive discharge was formed to create a population inversion at the infrared (IR) transitions of CO molecules. The temporal and energy characteristics of the radiation of the inductive CO2-laser depending on the duration of the pump pulse are investigated. The spatial characteristics and spectrum of the radiation of the developed laser are estimated. The divergence of the laser radiation was 0.52 mrad. The cross-sectional dimension of the laser output beam was about 35 mm in diameter. [ABSTRACT FROM AUTHOR]

The experimental results in studying lasing and pumping parameters of the CuBr laser with attypical excitation mode are presented in the paper. The excitation was provided by the single pulse mode with preliminary preparation of the active medium by pulse sequence (zug). The effect of the time delay between pulse sequence and single excitation pulse on the CuBr + Ne and CuBr + Ne + HBr media lasing was determined. It has been established that an increase in this time delay leads to an increase in the duration of the generation pulse. It was shown for the first time that lasing in a CuBr + Ne + HBr laser can be obtained with a relaxation time of the active medium up to 5 ms. The critical electron concentration which provides ability of generation for CuBr + Ne and CuBr + Ne + HBr media was experimentally shown. [ABSTRACT FROM AUTHOR]

The features of the formation of pulsed volume discharge in working mixtures of non-chain wide-aperture HF (DF) lasers are considered. It is shown that the spatial structure of the volume discharge in these lasers is characterized by several spatial dimensions. To register such plasma structures, the Talbot interferometry method is proposed, and a simple experimental setup capable of recording the fine microstructure of plasma channels in the gas discharge plasma of electrochemical lasers, as well as disturbances in the optical density of transparent media, is described. [ABSTRACT FROM AUTHOR]

The research studies of e-beam sustained discharge gas lasers initiated by Nikolai Basov in early 1970s made it possible to develop lasers based on the fundamental transitions of carbon monoxide molecule with high laser power and efficiency. Soon, under his scientific supervision, lasing on first-overtone transitions of CO molecule was obtained. Following these results, about ten years ago a compact slab CO laser excited by a repetitively pulsed capacitive RF discharge and cryogenic cooling of its electrodes, operating without forced pumping of its active medium was for the first time developed at the N.G. Basov Quantum Radiophysics Division of the P.N. Lebedev Physical Institute. At present, the average power of such lasers with active medium volume of ~ 35 cm3 reaches 40 W on CO molecule fundamental transitions (in the wavelength range of 5.06–5.92 μm) and 6 W on first-overtone transitions (λ = 2.60–3.05 μm). Under Q-switching, those repetitively pulsed lasers allow one to obtain laser emission with a peak power up to 5 kW which made it possible to apply them in experiments on laser radiation frequency conversion in nonlinear crystals into the spectral range of ~ 2–20 μm. [ABSTRACT FROM AUTHOR]

We present a method of synthesis of sp-carbon allotropes or carbynes. Linear chains of carbon atoms are obtained from graphite placed in a joint field of laser plasma and arc discharge. The combined action of laser and arc discharge allows to create conditions for the formation of a variety of carbon allotropes, whose structural composition is governed by the interplay of external fields. The method may be employed in the mass production of sp- and sp2- hybridized carbon for the needs of possible applications in micro and nanoelectronics, biosensing. [ABSTRACT FROM AUTHOR]

In contrast to conventional components made from a single material, hybrid multi-material components allow the production of load-adapted parts with different materials in different structural and functional areas. Hardenable and forgeable steels with a high carbon content are suitable for increasing fatigue and wear resistance and thus an extension of component life. However, materials with an equivalent carbon content of more than 0.6 are considered difficult to weld due to their tendency to crack. This study investigates the influence of the shielding gas coverage on the laser hot-wire cladding process with high carbon cladding material AISI 52100. For this reason, welding tests were carried out with different parameter combinations in a process chamber flooded with argon. The oxygen content in the chamber was less than 500 ppm during the welding process. The claddings welded in the process chamber are compared to the claddings welded in a previous investigation with a commercial shielding gas nozzle for laser deposition welding with wire. The tests conducted showed reduced pore formation and very little sparking. By using a process chamber, the average degree of dilution was reduced from 16.9% to 8.5% and burn-off of alloying elements was reduced. In most cases, high hardness values of 700 HV0.1 to 850 HV0.1 were achieved. The use of the process chamber demonstrates that the shielding gas coverage and therefore the remaining oxygen content have a high influence on the process stability and seam quality when welding high carbon steel. Such a considerable effect has not yet been observed with other commercially available cladding steels. [ABSTRACT FROM AUTHOR]

This study presents parametric evaluation and optimization of laser machining parameters of austenitic stainless steel 304 (SS 304) sheet. SS304 is a substantial manufacturing material machined by laser machining. The central composite design (CCD) of the response surface methodology (RSM) was utilized for the design of the experimental plan. Laser power, cutting speed, gas pressure and pulse frequency were used as process parameters, whereas kerf width and kerf taper were measured as performance characteristics. The factor effects on kerf width and kerf taper were analyzed using a surface plot. A good degree of fit was shown by the developed regression model. The analysis of variance results reveals that cutting speed, laser power and gas pressure had contributions of 41.49, 31.71 and 16.71% on kerf width, and 31.23, 26.03 and 19.81% on kerf taper. The optimal machining conditions of kerf width found at laser power of 1800 W, cutting speed of 1000 mm/min, gas pressure of 1.30 bar and a pulse frequency of 1500 Hz and of kerf taper at laser power of 1800 W, cutting speed of 802 mm/min, gas pressure of 1.30 bar and a pulse frequency of 1500 Hz. The higher cutting speed and gas pressure and lower laser power and pulse frequency result in the smallest kerf width, while an increase in cutting speed up to mid-level, higher gas pressure and lower laser power and pulse frequency result in the lower kerf taper. A mathematical model was developed to govern the relationship between the process parameters and the kerf width and kerf taper. The kerf width and kerf taper during the laser machining procedure are optimized efficiently through this method. It is clearly revealed that the performance characteristics of the laser machining process can be optimized efficiently by this method. [ABSTRACT FROM AUTHOR]

The effect of laser hardening and of gas nitriding on the microstructure and wear resistance of steel P20 (the Russian counterpart is 38KhNM) is studied. The phase composition and the microhardness of the hardened surface layers are determined and their microstructure is studied. Wear tests are performed. It is shown that both treatments raise the hardness of the steel. However, the nitrided layer has a higher resistance to plastic deformation, a higher indentation modulus, and a much higher wear resistance than the laser hardened layer. Laser hardening produces a deeper hardened layer, whereas gas nitriding provides a higher wear resistance of steel P20. [ABSTRACT FROM AUTHOR]

A series of experiments are conducted in a 37 cm diameter gas burner situated in a quiescent environment. Time-averaged local measurements of the temperature, velocity, soot, and gaseous species are obtained in 21kW, 34kW, and 50 kW propane fires above the burner centerline. Global measurements of the radiative fraction, flame height, soot and CO yields, and total heat feedback to the burner are also obtained. Time-averaged gaseous species concentrations are measured using a gas chromatograph with mass selectivity and thermal conductivity detectors. The time-averaged soot mass fraction is measured simultaneously via a gravimetric technique. Additional gaseous species and soot measurements are obtained in the exhaust duct via gas analyzers and laser transmission measurements, respectively. A mixture fraction analysis shows that these propane fires exhibit similar trends in which the experimental data nearly matches the idealized state relationships. Carbon monoxide concentrations obtained throughout the fire are presented as a function of mixture fraction and compared among the different propane fire sizes. The dataset provides a comprehensive picture of the mean structure of the three propane fires. [ABSTRACT FROM AUTHOR]

We present the first experimental results obtained with a setup created on the basis of the PEARL laser facility for studying the processes of generating terahertz radiation from laser wake fields which are formed during the propagation of a high-power femtosecond laser pulse in a rarefied plasma. In particular, the occurrence of terahertz generation in the case where the laser–plasma interaction region is located between a pair of dielectric prisms of total internal reflection is demonstrated. The dependence of the terahertz radiation energy on the energy of a femtosecond laser pulse and on the plasma density is studied. [ABSTRACT FROM AUTHOR]

The minimal values of the 2.45 GHz microwave electric field, which are necessary to maintain a discharge in a number of noble gases (argon, neon, and helium) in optical fibers with hollow cores of small diameter up to 100 μm, have been measured for the first time. The minimal electric field values for all three gases are (2.5–2.8) kV/cm at a pressure of argon ~50 Torr, neon ~300 Torr, and helium ~500 Torr. [ABSTRACT FROM AUTHOR]

This paper explored the influence of process parameters of laser cladding Ni35A + TiC composite coatings on the width, height, cross-sectional area, and wetting angle of single-track cladding on the cylindrical substrate by establishing prediction models based on Response Surface Methodology. The clad width was increased initially then flattened; however, increasing scanning speed and gas flow decreased the clad width. Accelerating scanning speed caused a reduction of clad height; increasing gas flow resulted in the increase of clad height. The cross-sectional area was broadened by larger laser power and gas flow, but the cross-sectional area was reduced under a faster scanning speed. A wider wetting angle was created by accelerating scanning speed and reducing gas flow. The process parameters were optimized and experimentally validated. The error rates for the width, height, cross-sectional area, and wetting angle were 3.702, 2.451, 6.094, and 0.085% respectively, indicating remarkable prediction accuracy. [ABSTRACT FROM AUTHOR]

A novel approach to stabilize the laser's discharge plasma impedance by trigger modulation is presented. The discharge plasma impedance of laser drops due to increased charge carriers during laser operation. The absence of intermittent high voltage discharge pulses provides enhanced time for recombining charge carriers, thus restricting the fall in the laser impedance. It has been observed that by missing 0.1% of discharge pulse, the drop in the laser voltage is improved from 4.3 to 2.3%, and an increase in the laser head current is limited to 3% from 3.6% in 6 h of laser operation. The drop in the optical output power is reduced by 10% at the end of 6 h. Further, the controlled intermittent discharge missing ceases the thermal loading at the cathode fall and lowers the probability of thermal instability in discharge plasma. This will improve the discharge stability and reduces the jitter in the metal vapor laser. We believe this approach of manipulating trigger to attain stable impedance and prevent instability, can be applied to other applications requiring high current large volume stable discharges. [ABSTRACT FROM AUTHOR]

The spatial distributions of the electron temperature and the emission intensity of the C2 molecular complex in a plasma jet of a continuous optical discharge in the mode of a laser plasmatron supported by the radiation of a cw CO2 laser operating on a mixture of Ar with molecular additives have been measured. Diamond coatings have been obtained on the cutting inserts of a turning tool made of WC8 hard alloy; diagnostics of the coatings have been carried out. [ABSTRACT FROM AUTHOR]

The constructed cylindrical and spherical models of a laser-plasma ion source of a portable neutron generator made it possible to analyze the dynamics of ion currents based on their representation in the form of the interaction of partial and limiting currents and to greatly simplify the numerical algorithm. For the selected parameters of the discharge gap and the laser, the values of ion currents at the cathode were obtained. The calculated values of ion currents were compared with experimental data. [ABSTRACT FROM AUTHOR]

By now technologies, employing optical discharges find ever expanding applications in metering and diagnostic equipment in science, engineering and medicine. Based on the original experimental results authors look into some manifestations of spatial and temporal instabilities of the continuous and periodic pulse optical discharges (COD, POD). Set of the phenomena considered makes a great impact on a performance of laser produced plasmas essential for many applications, such as high brightness broadband light sources, for instance. Performance instability of continuous optical discharges followed by laser beam refraction on the refraction index gradients exhibit themselves first in spatial inhomogeneity of plasma thermal radiation luminosity and the other parameters related. Spatial inhomogeneity is accompanied by temporal instability of the plasma. The paper reports criteria for the appearance of instabilities related to the refraction followed by the limitations on supporting of elongated plasma. One of the main reasons of temporal instabilities of COD is thermal gravity convection. Instability of a heated gas zone surrounding optical discharge is followed by regular self-sustained oscillations leading in turn to pulsing of brightness and position of radiated plasma. Simple physical model proposed gives estimations correspondent to the observed pulse frequency dependence on gas pressure. In the case of periodic pulse optical discharges forced convection may be put forward as one of the main discharge instability reasons. Pulse optical discharge induces convective flows due to asymmetrical gas expanding following gasdynamic effect of the energy release zone shape determined by laser beam focusing system configuration. [ABSTRACT FROM AUTHOR]

In recent years, foam materials have attracted people's attention in many fields. This study reveals the one-step preparation of polypropylene (PP) foam material with very low carbon nanotubes (CNTs) content via laser irradiation technology. A low-energy near-infrared (1064 nm) laser beam is used to scan the laser-sensitive PP/CNTs composite prepared in the air. The controllable instantaneous thermal energy generated by laser irradiation decomposes CNTs and PP, and forms a foaming layer in situ on the surface of the composite material. CNTs content, laser power and laser scanning rate are key parameters for controlling laser-induced foaming. The results show that the rich carbonized structure induced by the laser envelops the gas generated by thermal degradation to form a porous structure, and form a 3D white pattern with the naked eye. This study can provide a positive reference for directly writing 3D foamed structures on the surface of composite materials on a large scale through a simple and efficient one-step laser irradiation method. [ABSTRACT FROM AUTHOR]

Carbon fiber reinforced plastic (CFRP) is extensively used in automotive and aerospace industries with the aim to achieve reduction on emissions by reducing weight. Due to governmental regulations to reduce the environmental impact and to reduce waste, the need for remanufacturing CFRP is becoming an interesting area of application with economic benefits to industry. This is important as manufacturing carbon fiber is a costly process and remanufacturing CFRP is more cost effective and reduces the dependency on virgin materials. Processing CFRP to meet demands, for fast and high-quality cuts, can impose problems for conventional methods. The use of multi-pass scanning technique in laser cutting CFRP is investigated using a 1.5 kW fiber laser with assist gas pressure of 16 bar and gas flow rate of 126 lt/min. Using multi-pass technique, a through cut can be obtained by repeating the beam travel more than once. The advantage of laser cutting when compared with traditional CNC, is the low cost of maintenance over time due to the non-contact nature of the process i.e. no wear of tool at contact area. And due to the small beam spot size of the laser small and complex shapes can be cut. The aim of the paper is to determine how the process performs in terms of cutting speed and fiber damage. Average power was used to carried out experimental tests. A fiber damage below 100 µm with laser cutting speed of 2.5 m/min and above was obtained. Thermal effects were analyzed using scanning electron microscope (SEM) and optical microscope (OM). The fiber damage was further optimized using specialist methods such as double aperture nozzle and trenching. The use of trenching and double aperture further reduces the fiber damage to 10 µm and 50 µm, respectively with laser cutting speed of 7.5 m/min and 3.33 m/min. [ABSTRACT FROM AUTHOR]

Atmospheric pressure discharge plasma is widely utilized in industry and science. However, due to the spatiotemporal uncertainty of the natural discharge, it is difficult to measure the discharge plasma spectra with a high spatiotemporal resolution. This prevents the accurate investigation of discharge plasma evolution and limits further applications. Here, we harnessed a femtosecond laser filament to trigger and guide a high-voltage discharge, i.e., the discharge plasma channel is rigorously controlled by the filament in both space and time. Therefore, the spectra of the plasma channel with a high spatiotemporal resolution could be measured using an imaging spectrometer. The spectra of the whole process of femtosecond laser filament-triggered discharge plasma are thoroughly studied. According to the spectral emission features, the whole process is divided into three stages: femtosecond laser filamentation, streamer propagation, and discharge. The spectral emissions at different stages can be utilized as required according to the spectral emission features. Based on the spatiotemporally resolved spectra of the streamer, the streamer propagation velocity is calculated to be about 3 × 105 m/s. In addition, atomic emissions from a discharge plasma triggered by femtosecond laser filament can be used for one-dimensional component measurements of flow fields. [ABSTRACT FROM AUTHOR]

The work established the mathematical model of the powder ratio, laser power, scanning speed, and airflow rate on the hardness of the cladding layer and stomatal area based on the central composite design and response surface methodology to explore the coupling effect of the powder ratio and process parameters of the preset powder process in laser cladding on the performance and defects of the Ni35A + SiC cladding layer. The experimental results showed that the hardness increased with the increased powder ratio and scanning speed, and decreased with the increased laser power. The four selected process parameters affected the stomatal area, and the stomatal area could be reduced by increasing the laser power and gas flow rate and decreasing the scanning speed and powder ratio. The model accuracy was further verified with the optimization objectives of maximum hardness and minimum stomatal area, and the errors of the predicted and actual values of hardness and stomatal area were 0.9 and 4.07%, respectively. The results provide a theoretical basis for exploring the properties of SiC hard-phase cladding layers and the control and prediction of defects. [ABSTRACT FROM AUTHOR]

The paper presents a power supply based on the linear transformer driver topology concept for the excitation of metal halide vapors active elements. The main feature of the power supply is its modular structure, which allows increasing the output voltage and a change in storage capacity depending on the number of modules. Each module is designed to minimize parasitic parameters and provide high voltage and current slew rates to the gas discharge tube. The limit parameters of one module are as follows: a maximum output voltage of 1100 V and a maximum pre-pulse energy in the storage capacity of 9.0 mJ. A laboratory model of the power supply, based on six modules, was designed. The experimental results of the CuBr + Ne + HBr media excitation at different pulse repetition rates are presented. For the first time, a 1.5 W radiation power was obtained for the laser excited by this type of power supply. [ABSTRACT FROM AUTHOR]

Energy and temporal radiation characteristics of the pulsed inductive CO2 gas laser with RF excitation as the function of RF pump-pulse duration τ with xenon additions to a gas mixture of the laser have been experimentally investigated. This made it possible to develop an efficient pulsed inductive CO2 laser with an output energy E > 1.2 J (the efficiency η ~ 17%), using a He:N2:CO2:Xe gas mixture [the (Xe) = 4%]. In this case, the lasing pulse duration tpuls (a full width at half-maximum) was 3.5 ms at a τ = 10 ms. For the pulsed inductive CO2 laser with RF excitation, it was shown for the first time a xenon addition to a gas mixture made it possible to achieve an efficiency η ~ 27% at the output energy E more 600 mJ. Pulses of RF current propagated along the solenoid, and the inductive discharge was formed to create population inversion by IR transitions of CO2 molecules. [ABSTRACT FROM AUTHOR]

The historical aspect, present status, and future prospects of diode-pumped alkali lasers (DPAL) are discussed. DPAL is a relatively new laser, first reported in 2003. It is characterized by extremely high scalability, good beam quality by virtue of its gaseous laser medium, and intrinsically high efficiency because it is a three-level laser with a small Stokes defect. Because of these features, DPAL is being studied as a directed energy weapon and is also expected to find applications in industry and space. We propose the use of DPAL for space debris removal. Some of the research results of our group are also introduced. [ABSTRACT FROM AUTHOR]

The systems of active Brownian grains can be considered as open systems, in which there is an exchange of energy and matter with the environment. The collective phenomena of active Brownian grains can demonstrate analogies with ordinary phase transitions. We study the active Brownian motion of light-absorbing and strongly interacting grains far from equilibrium suspended in gas discharge under laser irradiation when the nature and intensity of the active motion depend on the effect of radiation. Active Brownian motion is caused by photophoresis, i.e., absorption of laser radiation at the metal-coated surface of the grain creates radiometric force, which in turn drives the grains. We experimentally observed the active Brownian motion of charged grains in the transition of the grain monolayer from the solid to liquid state. An analysis of the character of motion, including the mean-square and linear displacement and persistence length at various values of the randomization (coupling parameter) of the grain structure, was presented. [ABSTRACT FROM AUTHOR]

To explore the method of low-damage gas-assisted laser processing of carbon fiber reinforced plastics, using QCW450 quasi-continuous fiber laser cutting machine (maximum peak power 4500 W), and laser scribing carbon fiber reinforced plastics with three gas-assisted methods: coaxial nitrogen, coaxial oxygen, and coaxial oxygen paraxial nitrogen compound gas-assisted, and study the influence of the three on cutting quality. At the same time, the single factor experiment method is used to study the impact of laser peak power, scanning speed, and gas pressure on processing quality, mainly analyzing the size of the heat-affected zone of the cutting section, the cutting depth, and the width of the upper slit, and analyze the action mechanism of gas-assisted laser processing of carbon fiber reinforced plastics. The experimental results show that nitrogen can bring a certain cooling effect during high-power and high-speed processing. Oxidation exothermic effect of oxygen can promote the removal of thermal melting of materials, and high-pressure airflow can take away a part of the excess heat and erosion of the residual kerf. Meanwhile, the nitrogen and oxygen mixed gas assists comprehensively in reducing thermal damage and improving the feasibility of etching. The greater the laser peak power, the deeper the etching depth, and the greater the width of the heat-affected zone, the higher the cutting speed, the width of the heat-affected zone, and the cutting depth will decrease. Too much or too little gas pressure is not conducive to improving quality. This research provides a reference for low-damage gas laser processing carbon fiber reinforced plastics. [ABSTRACT FROM AUTHOR]

Acoustic resonances of an opto-acoustic detector (OAD) with differential cylindrical Helmholtz resonators are studied numerically upon variation of their main parameters. Dependences of quality factor of the acoustic resonance and the resonance frequency on geometric parameters of the OAD are obtained and analyzed. The results are of interest for development of opto-acoustic gas analyzers. [ABSTRACT FROM AUTHOR]

In this paper, a theoretical method is presented to calculate Brillouin linewidth (BLW) in gas mixtures. The presented model is based on Newton's viscosity law and the kinetic theory of gases. From a combination of Chapman–Enskog theory and Navier–Stokes mathematical model, we recovered the appropriate terms of the viscosity tensor for gas mixtures. We demonstrated that viscosity is not necessarily the dominant mechanism in the enhancement or suppression of the BLW in a gas mixture, and other parameters, such as density, can be dominant instead. It was found that the contribution of thermodynamics quantities was negligible compared to other parameters. The numerical results were also compared to those obtained from the molar refraction-mixing method and confirmed that these results were completely coherent. [ABSTRACT FROM AUTHOR]

We report the results of experimental and numerical investigations of a discharge KrF laser with specific pump power of 3.5 and 7 MW/cm3; generation is obtained with specific radiation pulse energy of about 6 and 9.5 J/L for an internal energy efficiency of about 4%. Time dependences of the formation of charged and excited particles in a dense excimer plasma with an electron concentration of ~1016 cm–3 are obtained. The conditions for effective operation of the laser are proposed, which will ensure a further increase in the specific radiation energy by more than two times with preserved high internal laser efficiency relative to the energy input into the discharge. [ABSTRACT FROM AUTHOR]

A method for measuring multiphoton absorption cross sections of Gaussian laser pulses in gases by means of an optoacoustic detector exhibiting temporal resolution (spectrophone) is developed. The functionality of the technique is tested using one- and three-photon absorption of nanosecond pulses of quasi-monochromatic radiation with a wavelength of 266 nm by molecular oxygen. [ABSTRACT FROM AUTHOR]

It has been experimentally shown that a low-power vacuum pinch discharge with laser ignition can emit a beam of abnormally accelerated electrons with maximum energies per unit charge almost an order of magnitude higher than the voltage across the discharge gap. It has been found that the intensity of the X-ray radiation generated when the beam is applied to the target significantly decreases with an increase in the laser pulse energy. The maximum energy of X-ray quanta is inversely proportional to the mass of the cathode substance ablated by laser radiation during discharge ignition. Possible mechanisms of the electron-beam generation process have been discussed. [ABSTRACT FROM AUTHOR]