The Experts below are selected from a list of 13014 Experts worldwide ranked by ideXlab platform
Xinwei Wang - One of the best experts on this subject based on the ideXlab platform.
-
phase change and stress wave in picosecond Laser Material Interaction with shock wave formation
Applied Physics A, 2013Co-Authors: Jingchao Zhang, Xinwei WangAbstract:When background gas is present in pulsed Laser–Material Interaction, a shock wave down to the nanoscale will emerge. The background gas will affect the phase change and explosion in the target. This study is focused on the void dynamics and stress wave in a model Material (argon crystal) under picosecond pulsed Laser irradiation. Our results show that existence of ambient gas and the shock wave significantly suppresses the void formation and their lifetime. Void dynamics, including their growing rate, lifetime, and size under the influence of ambient gas are studied in detail. All the voids undergo an accelerating and decelerating process in the growth. The collapsing process is almost symmetrical to the growing process. Higher Laser fluence is found to induce an obvious foamy structure. Stress wave formation and propagation, temperature contour, and target and gas atom number densities are studied to reveal the underlying physical processes. Although the Interaction of the plume with ambient gas significantly suppresses the void formation and phase explosion, no obvious effect is found on the stress wave within the target. Very interestingly, secondary stress waves resulting from re-deposition of ablated atoms and void collapse are observed, although their magnitude is much smaller than the directly Laser-induced stress wave.
-
Phase change and stress wave in picosecond Laser–Material Interaction with shock wave formation
Applied Physics A, 2013Co-Authors: Jingchao Zhang, Xinwei WangAbstract:When background gas is present in pulsed Laser–Material Interaction, a shock wave down to the nanoscale will emerge. The background gas will affect the phase change and explosion in the target. This study is focused on the void dynamics and stress wave in a model Material (argon crystal) under picosecond pulsed Laser irradiation. Our results show that existence of ambient gas and the shock wave significantly suppresses the void formation and their lifetime. Void dynamics, including their growing rate, lifetime, and size under the influence of ambient gas are studied in detail. All the voids undergo an accelerating and decelerating process in the growth. The collapsing process is almost symmetrical to the growing process. Higher Laser fluence is found to induce an obvious foamy structure. Stress wave formation and propagation, temperature contour, and target and gas atom number densities are studied to reveal the underlying physical processes. Although the Interaction of the plume with ambient gas significantly suppresses the void formation and phase explosion, no obvious effect is found on the stress wave within the target. Very interestingly, secondary stress waves resulting from re-deposition of ablated atoms and void collapse are observed, although their magnitude is much smaller than the directly Laser-induced stress wave.
-
Hybrid Atomistic-macroscale Modeling of Long-time Material Behavior in Nanosecond Laser-Material Interaction
International Photonics and Optoelectronics Meetings, 2012Co-Authors: Lijun Zhang, Xinwei WangAbstract:The thermo-physical properties and fundamental mechanism of Laser ablation process in nanosecond Laser-Material Interaction are investigated in a computational study combining molecular dynamics simulations.
-
plume splitting in pico second Laser Material Interaction under the influence of shock wave
Physics Letters A, 2009Co-Authors: Sobieslaw Gacek, Xinwei WangAbstract:Abstract In this work, molecular dynamics simulations are conducted to study the physics of plume splitting in pico-second Laser Material Interaction in background gas. The velocity distribution shows a clear split into two distinctive components. Detailed atom trajectory track reveals the behavior of atoms within the peaks and uncovers the mechanisms of peak formation. The observed plume velocity splitting emerges from two distinguished parts of the plume. The front peak of the plume is from the faster moving atoms and smaller particles during Laser–Material ablation. This region experiences strong constraint from the ambient gas and has substantial velocity attenuation. The second (rear) peak of the plume velocity originates from the larger and slower clusters in Laser-Material ablation. These larger clusters/particles experience very little constraint from the background, but are affected by the relaxation dynamics of plume and appear almost as a standing wave during the evolution. Density splitting only appears at the beginning of Laser–Material ablation and quickly disappears due to spread-out of the slower moving clusters. It is found that higher ambient pressure and stronger Laser fluence favor earlier plume splitting.
-
Plume splitting in pico-second Laser–Material Interaction under the influence of shock wave
Physics Letters A, 2009Co-Authors: Sobieslaw Gacek, Xinwei WangAbstract:Abstract In this work, molecular dynamics simulations are conducted to study the physics of plume splitting in pico-second Laser Material Interaction in background gas. The velocity distribution shows a clear split into two distinctive components. Detailed atom trajectory track reveals the behavior of atoms within the peaks and uncovers the mechanisms of peak formation. The observed plume velocity splitting emerges from two distinguished parts of the plume. The front peak of the plume is from the faster moving atoms and smaller particles during Laser–Material ablation. This region experiences strong constraint from the ambient gas and has substantial velocity attenuation. The second (rear) peak of the plume velocity originates from the larger and slower clusters in Laser-Material ablation. These larger clusters/particles experience very little constraint from the background, but are affected by the relaxation dynamics of plume and appear almost as a standing wave during the evolution. Density splitting only appears at the beginning of Laser–Material ablation and quickly disappears due to spread-out of the slower moving clusters. It is found that higher ambient pressure and stronger Laser fluence favor earlier plume splitting.
Lijun Zhang - One of the best experts on this subject based on the ideXlab platform.
-
Hybrid Atomistic-macroscale Modeling of Long-time Material Behavior in Nanosecond Laser-Material Interaction
International Photonics and Optoelectronics Meetings, 2012Co-Authors: Lijun Zhang, Xinwei WangAbstract:The thermo-physical properties and fundamental mechanism of Laser ablation process in nanosecond Laser-Material Interaction are investigated in a computational study combining molecular dynamics simulations.
-
hybrid atomistic macroscale modeling of long time phase change in nanosecond Laser Material Interaction
Applied Surface Science, 2008Co-Authors: Lijun Zhang, Xinwei WangAbstract:Abstract In this work, large-scale hybrid atomistic-macroscale simulation is performed to study the long-time Material behavior in nanosecond Laser–Material Interaction. Different phase change phenomena are studied, including solid–liquid interface speed, temperature, maximum melting depth, and ablation rate. Full solidification/epitaxial re-growth is observed within 60 ns for the Laser fluence of 5 J/m2. Strong fluctuation is observed at the solid–liquid interface and surface of the molten pool. No visible super-heating is observed at the solid–liquid interface. For the Laser fluences studied in this work, an almost linear relationship is observed between the ablation yield and the Laser fluence, indicating weak phase explosion.
-
Dynamic Structure and Mass Penetration of Shock Wave in Picosecond Laser-Material Interaction
Japanese Journal of Applied Physics, 2008Co-Authors: Lijun Zhang, Xinwei WangAbstract:This work pioneers the atomistic modeling of the shock wave in background gas in picosecond Laser-Material Interaction. It is found in the shock wave the compressed ambient gas region has a very uniform temperature distribution while the temperature decreases from the front of the plume to its end. The group velocity of atoms in the shock wave front is much smaller than the shock wave propagation speed and experiences a fast decay due to momentum exchange with the ambient gas. Strong decay of the shock wave front temperature and pressure is observed while its density features much slower attenuation. An effective mass penetration length is designed to quantitatively evaluate the mutual mass penetration between the plume and background gas. This effective mixing length grows at a rate of ~60 m/s. This fast mixing/mass penetration is largely due to the strong relative movement between the plume and the background gas. The molecular dynamics results agree well with the analytical solution in terms of relating various shock wave strengths.
-
Hybrid atomistic-macroscale modeling of long-time phase change in nanosecond Laser–Material Interaction
Applied Surface Science, 2008Co-Authors: Lijun Zhang, Xinwei WangAbstract:Abstract In this work, large-scale hybrid atomistic-macroscale simulation is performed to study the long-time Material behavior in nanosecond Laser–Material Interaction. Different phase change phenomena are studied, including solid–liquid interface speed, temperature, maximum melting depth, and ablation rate. Full solidification/epitaxial re-growth is observed within 60 ns for the Laser fluence of 5 J/m2. Strong fluctuation is observed at the solid–liquid interface and surface of the molten pool. No visible super-heating is observed at the solid–liquid interface. For the Laser fluences studied in this work, an almost linear relationship is observed between the ablation yield and the Laser fluence, indicating weak phase explosion.
-
Shock Waves in Pulsed Laser Material Interaction: Internal Structure and Mass Penetration
ASME 2008 First International Conference on Micro Nanoscale Heat Transfer Parts A and B, 2008Co-Authors: Lijun Zhang, Xinwei WangAbstract:This work pioneers the atomistic modeling of the shock wave in picosecond Laser-Material Interaction by simulating the Material that is irradiated with a picosecond Laser pulse (11.3 ps FWHM) in a 0.25 MPa background gas. The dynamic structure and mutual mass penetration between the plume and background gas are investigated in detail. In the shock wave the compressed ambient gas region has a very uniform temperature distribution while the temperature decreases from the front of the plume to its end. The group velocity of atoms in the shock wave front is much smaller than the shock wave propagation speed and experiences a fast decay due to momentum exchange with the ambient gas. Strong decay of the shock wave front temperature and pressure is observed while its density features much slower attenuation. An effective mixing length is designed to quantitatively evaluate the mutual mass penetration between the plume and background gas. This effective mixing length grows at a rate of ∼ 60 m/s. This fast mixing/mass penetration is largely due to the strong relative movement between the plume and the background gas. The MD results agree well with the analytical solution in terms of relating various shock wave strengths.Copyright © 2008 by ASME
Xiaochun Li - One of the best experts on this subject based on the ideXlab platform.
-
fabrication and application of micro thin film thermocouples for transient temperature measurement in nanosecond pulsed Laser micromachining of nickel
Sensors and Actuators A-physical, 2007Co-Authors: Hongseok Choi, Xiaochun LiAbstract:Abstract In order to investigate the complicated transient thermal phenomena in Laser micromachining, it is essential to accurately measure time-resolved temperatures of workpiece resulted from the transient Laser–Material Interaction. While numerous analytic and numerical models have been developed, little experimental results are available for a solid understanding of transient thermal phenomena in nanosecond pulsed Laser micromachining. In this paper, micro thin film thermocouples (TFTCs) with a high spatial and temporal resolution were fabricated on electroplated nickel substrates and used to measure transient surface temperatures in nanosecond pulsed Laser micromachining by ablation. Transient temperatures were successfully measured, and the effect of Laser energy fluences on peak temperatures was experimentally investigated. This study demonstrates that the micro TFTCs can be useful in measuring the transient temperatures micrometers away from the Laser–Material Interaction region on the workpiece during Laser micromachining, and the measured data could be utilized to validate and improve existing analytical and numerical models.
Milesa Sreckovic - One of the best experts on this subject based on the ideXlab platform.
-
numerical modelling of thermal effects on biological tissue during Laser Material Interaction
Physica Scripta, 2014Co-Authors: Z Latinovic, Milesa Sreckovic, M Janicijevic, J Ilic, J RadovanovicAbstract:Among numerous methods of the modelling of Laser Interaction with the Material equivalent of biological tissue (including macroscopic and microscopic cell Interaction), the case of pathogenic prostates is chosen to be studied. The principal difference between the inorganic and tissue equivalent Material is the term which includes blood flow. Thermal modelling is chosen for Interaction mechanisms, i.e. bio-heat equation. It was noticed that the principal problems are in selecting appropriate numerical methods, available mathematical program packages and finding all exact parameters for performing the needed calculations. As principal parameters, among them density, heat conduction, and specific heat, there are many other parameters which depend on the chosen approach (there could be up to 20 parameters, among them coefficient of time scaling, arterial blood temperature, metabolic heat source, etc). The Laser type, including its wavelength which defines the quantity of absorbed energy and dynamic of irradiation, presents the term which could be modulated for the chosen problem. In this study, the program Comsol Multiphysics 3.5 is used in the simulation of prostate exposed to Nd3+:YAG Laser in its fundamental mode.
-
Laser Interaction with Material theory experiments and discrepancies
Acta Physica Polonica A, 2009Co-Authors: Milesa Sreckovic, Z Latinovic, J Ilic, M Davidovic, B Djokic, ž Tomic, D DružijanicAbstract:The experimental treatment of chosen Material with Laser beams, starting from continuous wave up to fs pulses, produces the necessity to find the common and sophisticated theoretical approaches to Interaction modeling. For chosen Materials, some Laser treatment and damage analyses are performed. The provoked stresses and parameters of transport processes (penetration depth) are calculated by using the programs for electrical circuit analyses. Some inconsistencies in the treatment of large area Laser-Material Interaction are discussed.
-
drm md approach for modeling Laser Material Interaction with axial symmetry
Engineering Analysis With Boundary Elements, 2007Co-Authors: Radovan Gospavic, Viktor Popov, Milesa Sreckovic, Ching-shyang ChenAbstract:Abstract A dual reciprocity method multi-domain (DRM-MD) approach for modeling Laser–Material Interaction with axial symmetry was developed. The proposed approach is based on the fundamental solution for the Laplace equation in 2D and is much simpler for implementation than the dual reciprocity boundary element method (DRBEM) based on the fundamental solution for axisymmetric problems incorporating elliptic integrals. The thermal model of Laser–Material Interaction was applied for the cases of mono as well as multi-layer structures. Different aspects of Interaction up to the melting point of considered Materials are presented. The effect of temperature dependence of the absorption coefficients on the process of Laser heating was considered. Numerical results for spatial as well as temporal temperature distribution inside the Material bulk are presented and compared to analytical solutions.
-
DRM-MD approach for modeling Laser–Material Interaction with axial symmetry
Engineering Analysis with Boundary Elements, 2007Co-Authors: Radovan Gospavić, Viktor Popov, Milesa Sreckovic, Ching-shyang ChenAbstract:Abstract A dual reciprocity method multi-domain (DRM-MD) approach for modeling Laser–Material Interaction with axial symmetry was developed. The proposed approach is based on the fundamental solution for the Laplace equation in 2D and is much simpler for implementation than the dual reciprocity boundary element method (DRBEM) based on the fundamental solution for axisymmetric problems incorporating elliptic integrals. The thermal model of Laser–Material Interaction was applied for the cases of mono as well as multi-layer structures. Different aspects of Interaction up to the melting point of considered Materials are presented. The effect of temperature dependence of the absorption coefficients on the process of Laser heating was considered. Numerical results for spatial as well as temporal temperature distribution inside the Material bulk are presented and compared to analytical solutions.
-
Modelling of Laser-Material Interaction using semi-analytical approach
Mathematics and Computers in Simulation, 2004Co-Authors: Radovan Gospavić, Milesa Sreckovic, Viktor PopovAbstract:In this paper different aspects of Laser-Material Interaction were considered. Semi-analytical method was developed and applied to analysis of spatial and temporal distribution of temperature field inside bulk Materials. In particular, cases with cylindrical geometry, finite diameter and infinite length as well as cylindrical geometry, finite diameter and finite length were considered. For solving the governing partial differential equations (PDEs) the Laplace transform and the Fourier method of variables separation were used. In this way instead of the original governing PDEs, ordinary differential equations were solved. Particular solutions of the ordinary differential equations were used for evaluating the general solution, which was expressed in terms of series of particular solutions. The unknown coefficients in the series of particular solutions were determined using the boundary and initial conditions. The Laser-Material Interaction was represented using the thermal model. These Interactions for the cases of the high power Laser in pulse and continuous regime were analysed. The incident intensity of Laser radiation was under critical intensity.Using these methods the temperature field distribution was obtained in the Laplace transform domain. The convolution integral and the Green function were used to determine the temperature field in time domain. General semi-analytical methods and numerical solutions of appropriate transcendent equations were considered and numerical results for Al specimens were presented. The influences of Laser beam parameters to the temperature field distribution and isothermal curves inside the bulk Material were evaluated.
Fukuhisa Matsuda - One of the best experts on this subject based on the ideXlab platform.
-
Laser Material Interaction and process sensing in underwater nd yttrium aluminum garnet Laser welding
Journal of Laser Applications, 2003Co-Authors: Xudong Zhang, Eiji Ashida, Wuzhu Chen, Fukuhisa MatsudaAbstract:Laser–Material Interaction and process sensing technology for local-dry underwater Nd:yttrium–aluminum–garnet Laser beam welding were studied. The optical emissions induced by Laser–water Interaction were detected with an infrared (IR) optical sensor and observed with a charge coupled device camera. It was found that under Laser irradiation, a kind of water–vapor plasma formed immediately above the water surface if the water depth was more than 3 mm. This plasma severely reduced the Laser power reaching the workpiece. The water above the workpiece surface must be excluded by forming a local-dry cavity so as to perform underwater Laser welding. In local-dry underwater Laser welding, a coaxial gas-shielding nozzle was used to form a local-dry cavity. The IR optical signal and weld bead shape variations with various shielding conditions of the local-dry cavity were investigated. The experimental results showed that the IR signals could reflect well the status of the local-dry cavity and predict the weld qual...
-
Laser–Material Interaction and process sensing in underwater Nd:yttrium–aluminum–garnet Laser welding
Journal of Laser Applications, 2003Co-Authors: Xudong Zhang, Eiji Ashida, Wuzhu Chen, Fukuhisa MatsudaAbstract:Laser–Material Interaction and process sensing technology for local-dry underwater Nd:yttrium–aluminum–garnet Laser beam welding were studied. The optical emissions induced by Laser–water Interaction were detected with an infrared (IR) optical sensor and observed with a charge coupled device camera. It was found that under Laser irradiation, a kind of water–vapor plasma formed immediately above the water surface if the water depth was more than 3 mm. This plasma severely reduced the Laser power reaching the workpiece. The water above the workpiece surface must be excluded by forming a local-dry cavity so as to perform underwater Laser welding. In local-dry underwater Laser welding, a coaxial gas-shielding nozzle was used to form a local-dry cavity. The IR optical signal and weld bead shape variations with various shielding conditions of the local-dry cavity were investigated. The experimental results showed that the IR signals could reflect well the status of the local-dry cavity and predict the weld qual...
-
Laser-Material Interaction and process sensing in underwater Nd:YAG Laser welding
International Congress on Applications of Lasers & Electro-Optics, 2002Co-Authors: Xudong Zhang, Wuzhu, Eiji Ashida, Fukuhisa MatsudaAbstract:Process monitoring is one key problem for the quality assurance of underwater Laser beam welding (LBW) which is growing importance with the requirement on the maintenance and repair of nuclear facilities. In this paper, the Laser-Material Interaction and the sensing technology of welding process with infrared optical sensor was discussed. It was found that a kind of plasma with strong ultraviolet emission and strong shielding effect to Laser beam forms if the high-power Laser beam irradiates to even several millimeters deep water. So a gas-shielding nozzle was used to form local dry cavity. The relationship between the detected optical signals and the weld quality under various shielding conditions of local dry cavity was studied. The result shows that the detected signal well reflects the status of the local dry cavity and the optimal shielding condition could be determined from the amplitude of the signal.Process monitoring is one key problem for the quality assurance of underwater Laser beam welding (LBW) which is growing importance with the requirement on the maintenance and repair of nuclear facilities. In this paper, the Laser-Material Interaction and the sensing technology of welding process with infrared optical sensor was discussed. It was found that a kind of plasma with strong ultraviolet emission and strong shielding effect to Laser beam forms if the high-power Laser beam irradiates to even several millimeters deep water. So a gas-shielding nozzle was used to form local dry cavity. The relationship between the detected optical signals and the weld quality under various shielding conditions of local dry cavity was studied. The result shows that the detected signal well reflects the status of the local dry cavity and the optimal shielding condition could be determined from the amplitude of the signal.
