Papers by Keyword: Laser

Abstract: The Terahertz radiation generation through laser plasma interactions has attracted significant attention due to its wide range of applications in the field of spectroscopy, imaging, communications and medical. This work explores the variation of nonlinear current in the plasma which is the essential driver for Terahertz radiation generation. When intense laser pulses interact with plasma, a nonlinear ponderomotive force is generated, which leads to oscillations of plasma electrons. The oscillating electrons generate a nonlinear current, and their oscillation frequency causes the emission of Terahertz radiation. These nonlinear currents play a crucial role in exciting low-frequency electromagnetic waves in the THz regime. We analyze how the nonlinear current varies with key plasma parameters, including laser intensity, plasma density, magnetic field, and beam width. Theoretical modeling and numerical simulations demonstrate how optimizing these parameters enhances nonlinear current. Our results provide insights into controlling and optimizing nonlinear plasma currents for enhanced THz generation, offering promising advancements in plasma-based THz sources. This paper presents a theoretical model to describe the variation of nonlinear current as a function of these parameters, and investigated how laser beating can modify the plasma response for terahertz radiation generation.

Abstract: The paper presents new data on the complex use of colloidal solutions of nanoparticles (NPs) and low-intensity laser radiation on the biosynthetic activity of the edible medicinal mushroom Lentinula edodes (L. edodes) in vitro. Traditional mycological methods, colloidal solutions of metals (Ag, Fe, and Mg NPs), and unique photobiological methods were used. An argon laser at wavelength of 488 nm was used as a source of coherent visible light. It was found that colloidal solutions of NPs of all used metals increased (26–39%) the growth characteristics of L. edodes, while irradiation of the fungus inoculum with laser light in a medium with NPs reduced the growth activity of the L. edodes mycelium. The addition of all NPs to the nutrient medium with the inoculum inhibited the synthesis of extracellular polysaccharides, the greatest effect was observed with Fe NPs. At the same time, laser light irradiation in the presence of NPs increased the amount of extracellular polysaccharides; the greatest effect was observed in photoinduced Mg NPs, which stimulated the synthesis of extracellular polysaccharides by 47%. The introduction of NPs into the inoculum reduced the amount of intracellular polysaccharides in the mycelial mass; the greatest inhibitory effect of 50% was observed for Ag NPs. At for the photoinduced NPs, they stimulated the synthesis of intracellular polysaccharides in the mycelial mass of L. edodes. Treatment of the inoculum in a medium with NPs and photoinduced NPs caused an intensification of the synthesis of phenolic compounds in the mycelial mass and an increase in radical scavenging activity (RSA). The highest RSA values were recorded for samples obtained from inoculum treatment with photoinduced Fe and Mg NPs, respectively, for methanol and ethanol extracts of mycelial mass. The obtained results suggest the possibility of complex use of colloidal solutions of Fe, Ag, and Mg NPs and low-intensity laser radiation as environmentally friendly factors regulating biosynthetic activity in biotechnology of cultivating the valuable medicinal fungus L. edodes.

Abstract: The purpose of this study is to explore the use of laser additive manufacturing of bamboo powder to produce items with fewer variations than the traditional heat press method using a die. Although metal and resin powders are commonly used in powder additive manufacturing, bamboo powder presents unique challenges owing to its lack of material uniformity, low carbonization temperature, and dependence on pressure for adhesion. To address these issues, the appropriate laser power and irradiation time were determined by irradiating the laser at several power levels and examining its effects on the powder temperature and chemical changes during molding. The results indicated that rapid heating occurred at approximately 150 °C, and carbonization began at approximately 190 °C. As the energy loss for carbonization decreases with increasing laser power, this method is expected to be effective for producing bamboo products with fewer variations. In addition, restriction of continuous oxygen inflow by the glass plate lid makes it feasible to prevent heat generation and carbonization. Furthermore, pressurization by the glass plate makes it feasible to improve adhesion. Future research will focus on the suppression of carbonization by inert gas and heating at low temperatures for long periods of time, as well as the effects of different magnitudes of pressure on the process.

Abstract: In this work, we report a size-dependent study of Pd nanostructured films fabricated by ns pulsed laser on its plasmonic properties. More explanation and analysis of some results taken from our previous work are conducted. Statistical studies of the size distribution for different Pd films irradiated with the laser fluences (0.5, 0.75, and 1 J/cm²) are presented. For the three above fluences, an average diameter of (94±2, 38±0.8, and 44±1 nm) was calculated, respectively.

Abstract: Experimental work was focused on the restoration of functional surfaces of shaped parts of the molds for high-pressure casting of aluminum alloys. Paper presents results of the research aimed at determination of the quality of renovation layers applied by laser technology and TOP TIG technology. The TruDisk 4002 solid-state disk laser and the AirLiquide TOPTIG 220 welding power source were used to create the layers. Clad was applied to the base material of nickel-chromium-molybdenum vanadium steel 1.2714, DIN-56NiCrMoV7, with a hardness of 44 HRC. Uddeholm Deivar 1.2344, DIN-X40CrMoV51 wire with a 1.2 mm diameter was used as an additive material. The clad quality was evaluated using the light and electron microscopy and EDX microanalysis. The size of the heat affected zone (HAZ) and the presence of internal defects in the clads were determined. HAZ was set as max. a min. Value. Experimental work was supplemented by evaluation of tribological properties of clads by Pin-on-disc method.

Abstract: The development of the technology for laser hardening of the axle seats of rail vehicles aims to improve the high-cycle service life of these axles under wheel pressing and thus to increase safety in rail transport. Laser hardening can create high compressive stresses that increase the fatigue resistance of the material. The paper will present the results of this development on the EA1N material together with the documentation of the microstructure, hardness profiles and correlations with the internal residual stresses as well. These compressive stresses can play a crucial role in significantly increasing the fatigue resistance of the axles under operation.

Abstract: Two types of graphite cast iron are evaluated. The effect of laser surface hardening is compared using metallographic analysis of the microstructure and measurement of hardness profile. Conditions of the hardening were the same for both analyzed materials. The alloys that were compared are: cast iron with lamellar graphite EN GJL-200 and cast iron with nodular graphite EN GJS-700 CuNi. Microstructure of tested cast irons was pearlitic-ferritic. Laser surface heat treatment caused formation of martensitic layer. The depth and structural compositions of hardened layers do differ. In the case of gray cast iron the higher hardened depth was achieved and in the case of ductile cast iron the higher hardness was observed.

Abstract: Within this paper, we will present the results of a study on the ohmic contact formation process with nanosecond (ns) pulsed UV lasers. For the study we compared two laser processes: The base line process with a 100-300 ns pulsed laser with Gaussian beam profile and the 3D-Micromac AG process with a 50-100 ns pulsed laser with top hat beam profile. The forward voltage characteristics at wafer level was analyzed and proves a clear benefit of the top hat laser process. Besides, the forward voltage characteristics of a second run was performed to analyze the influence of increasing energy density to the electrical characteristic of heat sensitive front side structures. Also with high energy density no negative influence could be detected.

Abstract: The article presents the simulation of part distortion during laser metal deposition and a comparison of its results with the deposition performed in experiment. A numerical methodological approach to simulation is viewed which involves dividing the deposited material into primitive solids and further heating and cooling of each primitive solid along the deposition trajectory instead of simulating a moving heat source.

Abstract: This present work is about simulating and analysing a Vertical Cavity Surface Emitting Laser (VCSEL) structure used in optical fibre communication systems. In this paper a VCSEL structure made of seven Quantum Wells of Indium Gallium Arsenide Phosphide (InGaAsP) emitting at 1550 nm is simulated. The device is analysed looking at the following characteristics: Direct current current and voltage (IV) characteristics, light power against electrical bias, optical gain against electrical bias, light distribution over the structure, output power and threshold current. Specification of material characteristics, ordinary physical models settings, initial VCSEL biasing, mesh declarations, declaration of laser physical models, their optical and electrical parameters were defined using Atlas syntax. Mirror ratings and quantum wells are the two main parameters that were studied and analysed to come up with structure trends. By determining important device parameters such as proper selection of the emission wavelength and choice of material; a VCSEL with an output power of 9.5 mW was simulated and compared with other structures.