The Experts below are selected from a list of 152640 Experts worldwide ranked by ideXlab platform
Xinwei Wang - One of the best experts on this subject based on the ideXlab platform.
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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.
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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.
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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.
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Secondary shock wave in Laser-Material interaction
Journal of Applied Physics, 2008Co-Authors: Sobieslaw Gacek, Xinwei WangAbstract:In this work, the effects of shock driven process of the Laser-ablated argon plume in a background gas environment are explored via molecular dynamics simulations. The primary shock wave propagation and its influence on the backward motion of the target Material are delineated. It is observed that the strong pressure gradient inside the main shock wave overcomes the forward momentum of the plume and some compressed gas, leading to backward movement and redeposition on the target surface. Reflection of the backward moving gas on the target surface results in the secondary shock wave. Detailed investigation of the secondary shock wave phenomenon is provided, which gives, for the first time, an insight into formation and evolution of the internal gaseous shock at the atomistic level.
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nanodomain shock wave in near field Laser Material interaction
Physics Letters A, 2007Co-Authors: Xuhui Feng, Xinwei WangAbstract:Abstract In this work, molecular dynamics simulation is conducted to explore the shock wave phenomena in a nanodomain in near-field Laser–Material interaction. A large system consisting of over 800,000 atoms is studied. The work focuses on the kinetic and physical properties of the disturbed gas compression driven by the high speed movement of the molten particulates ejected from the solid target in a nanodomain. The quick interaction between solid and gas atoms compresses the gas and forms a steep shock wave front, which moves at a supersonic speed. The fast compression of gas also induces a steep interface of density, temperature and pressure distribution, which is viewed as typical characteristics of nanoscale shock waves. Evolutions of shock wave front position, velocity and Mach number are also explored and show quick decay during wave propagation.
Brian M Walsh - One of the best experts on this subject based on the ideXlab platform.
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cr er tm ho yttrium aluminum garnet Laser exhibiting dual wavelength lasing at 2 1 and 2 9 μm spectroscopy and Laser performance
Journal of Applied Physics, 2002Co-Authors: Brian M Walsh, Keith E Murray, Norman P BarnesAbstract:Over 1.0 J of 2.1 μm Laser energy and over 0.5 J of 2.9 μm Laser energy have been demonstrated in a single flashlamp pumped solid state Laser Material, specifically Cr:Er:Tm:Ho:YAG. Flashlamp pumped Laser operation of Ho:YAG at 2.1 μm and Er:YAG at 2.9 μm in various host Materials is well known. We have developed an innovative Laser system that operates at each of these wavelengths independently or simultaneously in a single solid state Laser Material with performance comparable to single wavelength systems Er:YAG and Cr:Tm:Ho:YAG. Variation of the flashlamp pump pulse length provides a method to discriminate between lasing at 2.1 and 2.9 μm. This effect results from Er→Tm→Ho energy transfer, the short lifetime of the upper lasing manifold in Er, the 4I11/2 manifold, and the relatively long upper Laser level lifetime in Ho, the 5I7 manifold. This simple tuning method of achieving two widely separated wavelengths without the use of optical tuning elements has potential applications in remote sensing and me...
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compositionally tuned 0 94 spl mu m Lasers a comparative Laser Material study and demonstration of 100 mj q switched lasing at 0 946 and 0 9441 spl mu m
IEEE Journal of Quantum Electronics, 2001Co-Authors: Brian M Walsh, Norman P Barnes, R L Hutcheson, Randy W EquallAbstract:A new and innovative composite Laser Material Nd:YAG/sub x/YSAG/sub 1-x/ has been developed with several objectives in mind; tunability, efficiency, and minimization of the deleterious effects of amplified spontaneous emission (ASE) in Q-switched operation. Wavelength tuning to the requisite wavelength 0.9441 /spl mu/m was achieved by using the technique referred to as compositional tuning; that is, using nonstoichiometric Laser Materials to shift the wavelength for precise tuning. Laser efficiency was achieved by studying the physics of 0.94-/spl mu/m transitions in nonstoichiometric Materials; i.e., by examining the effects of the host on the linewidth and cross section of of 0.94 /spl mu/m neodymium (Nd) transitions, ASE was minimized by choosing Materials with a small ratio of 1.06- to 0.94-/spl mu/m peak cross sections. A comparative study of six different Nd-doped mixed garnet Laser Material systems was performed to meet the objectives above. Within these six Material systems, over 20 Laser Materials were spectroscopically analyzed. The optimal Laser Material was found to be Nd:YAG/sub x/YSAG/sub 1-x/, which has been demonstrated to lase at the preselected wavelength of 0.9441 /spl mu/m, an important wavelength for remote sensing of water vapor. Operating this Laser on the /sup 4/F/sub 3/2//spl rarr//sup 4/I/sub 9/2/ transition in Nd:YAG/sub 0.18/YSAG/sub 0.82/ at 0.9441 /spl mu/m, has produced for the first time over 100 mT in the Q-switched mode. This represents one of the few Lasers that have been designed to operate at a specific, user-preselected wavelength.
Norman P Barnes - One of the best experts on this subject based on the ideXlab platform.
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cr er tm ho yttrium aluminum garnet Laser exhibiting dual wavelength lasing at 2 1 and 2 9 μm spectroscopy and Laser performance
Journal of Applied Physics, 2002Co-Authors: Brian M Walsh, Keith E Murray, Norman P BarnesAbstract:Over 1.0 J of 2.1 μm Laser energy and over 0.5 J of 2.9 μm Laser energy have been demonstrated in a single flashlamp pumped solid state Laser Material, specifically Cr:Er:Tm:Ho:YAG. Flashlamp pumped Laser operation of Ho:YAG at 2.1 μm and Er:YAG at 2.9 μm in various host Materials is well known. We have developed an innovative Laser system that operates at each of these wavelengths independently or simultaneously in a single solid state Laser Material with performance comparable to single wavelength systems Er:YAG and Cr:Tm:Ho:YAG. Variation of the flashlamp pump pulse length provides a method to discriminate between lasing at 2.1 and 2.9 μm. This effect results from Er→Tm→Ho energy transfer, the short lifetime of the upper lasing manifold in Er, the 4I11/2 manifold, and the relatively long upper Laser level lifetime in Ho, the 5I7 manifold. This simple tuning method of achieving two widely separated wavelengths without the use of optical tuning elements has potential applications in remote sensing and me...
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compositionally tuned 0 94 spl mu m Lasers a comparative Laser Material study and demonstration of 100 mj q switched lasing at 0 946 and 0 9441 spl mu m
IEEE Journal of Quantum Electronics, 2001Co-Authors: Brian M Walsh, Norman P Barnes, R L Hutcheson, Randy W EquallAbstract:A new and innovative composite Laser Material Nd:YAG/sub x/YSAG/sub 1-x/ has been developed with several objectives in mind; tunability, efficiency, and minimization of the deleterious effects of amplified spontaneous emission (ASE) in Q-switched operation. Wavelength tuning to the requisite wavelength 0.9441 /spl mu/m was achieved by using the technique referred to as compositional tuning; that is, using nonstoichiometric Laser Materials to shift the wavelength for precise tuning. Laser efficiency was achieved by studying the physics of 0.94-/spl mu/m transitions in nonstoichiometric Materials; i.e., by examining the effects of the host on the linewidth and cross section of of 0.94 /spl mu/m neodymium (Nd) transitions, ASE was minimized by choosing Materials with a small ratio of 1.06- to 0.94-/spl mu/m peak cross sections. A comparative study of six different Nd-doped mixed garnet Laser Material systems was performed to meet the objectives above. Within these six Material systems, over 20 Laser Materials were spectroscopically analyzed. The optimal Laser Material was found to be Nd:YAG/sub x/YSAG/sub 1-x/, which has been demonstrated to lase at the preselected wavelength of 0.9441 /spl mu/m, an important wavelength for remote sensing of water vapor. Operating this Laser on the /sup 4/F/sub 3/2//spl rarr//sup 4/I/sub 9/2/ transition in Nd:YAG/sub 0.18/YSAG/sub 0.82/ at 0.9441 /spl mu/m, has produced for the first time over 100 mT in the Q-switched mode. This represents one of the few Lasers that have been designed to operate at a specific, user-preselected wavelength.
Xianfan Xu - One of the best experts on this subject based on the ideXlab platform.
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Molecular Dynamics Simulation of Heat Transfer and Phase Change During Laser Material Interaction
Journal of Heat Transfer, 2002Co-Authors: Xinwei Wang, Xianfan XuAbstract:In this work, heat transfer and phase change of an argon crystal irradiated by a picosecond pulsed Laser are investigated using molecular dynamics simulations. The result reveals no clear interface when phase change occurs, but a transition region where the crystal structure and the liquid structure co-exist. Superheating is observed during the melting and vaporizing processes. The solid-liquid interface is found to move with a velocity of hundreds of meters per second, and the vapor is ejected from the surface with a vapor front velocity, of hundreds of meters per second.
Randy W Equall - One of the best experts on this subject based on the ideXlab platform.
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compositionally tuned 0 94 spl mu m Lasers a comparative Laser Material study and demonstration of 100 mj q switched lasing at 0 946 and 0 9441 spl mu m
IEEE Journal of Quantum Electronics, 2001Co-Authors: Brian M Walsh, Norman P Barnes, R L Hutcheson, Randy W EquallAbstract:A new and innovative composite Laser Material Nd:YAG/sub x/YSAG/sub 1-x/ has been developed with several objectives in mind; tunability, efficiency, and minimization of the deleterious effects of amplified spontaneous emission (ASE) in Q-switched operation. Wavelength tuning to the requisite wavelength 0.9441 /spl mu/m was achieved by using the technique referred to as compositional tuning; that is, using nonstoichiometric Laser Materials to shift the wavelength for precise tuning. Laser efficiency was achieved by studying the physics of 0.94-/spl mu/m transitions in nonstoichiometric Materials; i.e., by examining the effects of the host on the linewidth and cross section of of 0.94 /spl mu/m neodymium (Nd) transitions, ASE was minimized by choosing Materials with a small ratio of 1.06- to 0.94-/spl mu/m peak cross sections. A comparative study of six different Nd-doped mixed garnet Laser Material systems was performed to meet the objectives above. Within these six Material systems, over 20 Laser Materials were spectroscopically analyzed. The optimal Laser Material was found to be Nd:YAG/sub x/YSAG/sub 1-x/, which has been demonstrated to lase at the preselected wavelength of 0.9441 /spl mu/m, an important wavelength for remote sensing of water vapor. Operating this Laser on the /sup 4/F/sub 3/2//spl rarr//sup 4/I/sub 9/2/ transition in Nd:YAG/sub 0.18/YSAG/sub 0.82/ at 0.9441 /spl mu/m, has produced for the first time over 100 mT in the Q-switched mode. This represents one of the few Lasers that have been designed to operate at a specific, user-preselected wavelength.
