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Calculation of the extreme-ultraviolet radiation conversion efficiency for a laser-produced tin plasma source
摘要： This article presents the calculation results on the conversion efficiency (CE) of 1.064 μm laser-produced plasmas (LPPs) extreme-ultraviolet (EUV) tin (Sn) light sources with the Gaussian and a triangular-flat-topped like laser pulse temporal shapes. The computational model includes a collisional-radiative model and 1D hydrodynamics code that predicts reported experimental and theoretical results on the CE of 1.064 μm and 10.6 μm LPP EUV sources with the planar and mass-limited spherical Sn targets. The calculations for the case of a spherical target reveal that an optimum triangular-flat-topped like laser pulse generates a higher CE compared to the Gaussian pulse, especially, for the longer laser pulse duration than ~30 ns. The study demonstrated that a rising intensity rate of the laser pulse has a vital role to optimize the CE as well as to prolong the in-band (13.5 ± 0.135 nm) spectral emission of a small Sn spherical target. The model predicts a ~30 ns rising time duration for a linearly increasing intensity of triangular-flat-topped 1.064 μm laser pulse is necessary to obtain a maximum CE with a typical ~40 μm diameter liquid Sn droplet.
关键词： Extreme-ultraviolet lithography,Collisional-radiative model,Laser-produced plasmas,Radiation-hydrodynamics,Highly-charged tin spectra
更新于2025-09-19 17:13:59
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[IEEE 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - Sozopol, Bulgaria (2019.9.6-2019.9.8)] 2019 IEEE 8th International Conference on Advanced Optoelectronics and Lasers (CAOL) - Analysis of The Main Hydrodynamic Mechanisms in Laser Induced Keyhole Welding
摘要： Adequate modeling of additive laser technologies and laser welding requires a comparative analysis of the main hydrodynamic mechanisms and modes. The melt hydrodynamics during laser processing can be generated by the vapor recoil pressure and the thermocapillary effect. Analysis of the measured values of melt flow velocity at the front wall of keyhole and other measured parameters accompanying the welding allows to reveal the role of each mechanism. It is shown that the hydrodynamics in this case are determined by the thermocapillary shear flow in the thin surface layer at the negligible evaporation.
关键词： keyhole hydrodynamics,Additive technology,laser welding
更新于2025-09-19 17:13:59
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[IEEE 2019 Systems of Signal Synchronization, Generating and Processing in Telecommunications (SYNCHROINFO) - Russia (2019.7.1-2019.7.3)] 2019 Systems of Signal Synchronization, Generating and Processing in Telecommunications (SYNCHROINFO) - Simulation of Readiness Coefficient of FOCL with Temperature Actions on Optical Fibers
摘要： We have bridged the unsteady and steady mechanisms of underwater propulsion in nature and engineering by colocating their flapping and steady lifting surfaces in an outwardly conventional propulsor. The feasibility is indicated by the observation of overlap in the mechanisms in propulsion density versus displacement volume from 0.1 to 1 m . Such an overlap also exists between natural and engineered flyers. A novel, 0.7-m diameter, propulsor has been built where the fins, twistable along their span (0 to 30 ), can either slosh (where roll, pitch, and twist of the fins vary independently) or spin (where the rotational rate, fin pitch, and twist vary independently). Here, we discuss the origin of the novelty of the propulsor, the production of small thrust by slosh and propeller (prop) modes, the control of thrust amplitude by spanwise twisting of the fin, and the abrupt reversing of thrust. The tow speeds are low and close to the minimum induced velocity required for thrust onset by the flapping mechanism in the present propulsor—0 to 0.09 m/s, the fin chord 8, 250, and Reynolds number and shaft input power being 1 W. Time-averaged measurements show that thrust is more sensitive to pitch amplitude than to twisting during hovering, an effect that is reversed during slow towing due to the reduction in the spanwise variation of angle of attack. During towing, twist is more effective in the slosh mode than in the prop mode. Steady and quasi-steady thrust modeling is done to compare with prop- and slosh-mode measurements, respectively. The departures of the models are interpreted to mean that the beneficial effects of twist on the leading edge vortex (LEV) augment slosh forces and the rotational effects are detrimental to prop forces. We present simultaneous videography of fins during twisting and thrust reversal, and of thrust time trace as direct evidence of the relationship of cause and effect. Spanwise fin twisting is used to show that near-zero levels of thrust (0 to 1 N in steps of approximately 0.1 N) can be produced in both the slosh and prop modes and can be controlled merely by twisting the fins while keeping all other fin parameters unchanged. Transient-free reversal of the thrust direction has been achieved in the slosh mode while maintaining the same absolute value of thrust. However, thrust reversal in the prop mode is not transient free. This prop-mode transient is weaker due to the change in sign of the pitch angle but a change in the direction of the hub rotation produces a large spike and the reasons are discussed. Fine thrust control with individual fin hydrodynamics at the source that involves the lowest change in inertia is smoother. Smooth thrust reversibility is clearly identified as a unique property of flapping fin hydrodynamics. The mechanism overlap occurs because both fin modes have similar low transitional Reynolds numbers. Dynamical system models of unsteady hydrodynamics and control are shown to be similar suggesting that animal swimmers control vortex shedding ion-by-ion and animal-like motion control is theoretically possible with the proposed propulsor in the slosh mode but not in the prop mode.
关键词： hydrodynamics,oscillating propulsor,nonlinear control,force transient,Bioinspiration
更新于2025-09-19 17:13:59
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Influence of surface tension on the molten pool morphology in laser melting
摘要： The surface tension plays an important role in the distribution and evolution of molten pool morphology during laser melting. In this paper, based on the theory of Smoothed Particles Hydrodynamics (SPH), a mathematical model of surface tension on the molten pool morphology is established with the temperature change of molten pool being taken into account. The longitudinal morphology of molten pool and its formation process are simulated by using the SPH method under certain processing parameters, and the distributions of length and depth of molten pool are thoroughly analyzed at various processing parameters. The result shows that the longitudinal morphology of molten pool varying along the longitudinal section of solidified track presents a curve due to the influence of surface tension. A strong influence of Marangoni force on the flow of liquid metal and transformation of heat is also found. Moreover, the longitudinal morphology of a molten pool looks like that of a wave in the simulation; the deformation distributions of the longitudinal morphology of molten pool will increase with increasing laser power or decreasing scanning speed. The longitudinal morphologies of solidified molten pool are observed in the current experiments, and the experimental results are found to be agreed well with the calculated ones.
关键词： Processing parameters,Laser melting,Smoothed particles hydrodynamics (SPH),Molten pool morphology,Surface tension
更新于2025-09-16 10:30:52
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Symmetrical Bi-Heterojunction Alternating Current Ultraviolet Light-Emitting Diode
摘要： We have bridged the unsteady and steady mechanisms of underwater propulsion in nature and engineering by colocating their flapping and steady lifting surfaces in an outwardly conventional propulsor. The feasibility is indicated by the observation of overlap in the mechanisms in propulsion density versus displacement volume from 0.1 to 1 m . Such an overlap also exists between natural and engineered flyers. A novel, 0.7-m diameter, propulsor has been built where the fins, twistable along their span (0 to 30 ), can either slosh (where roll, pitch, and twist of the fins vary independently) or spin (where the rotational rate, fin pitch, and twist vary independently). Here, we discuss the origin of the novelty of the propulsor, the production of small thrust by slosh and propeller (prop) modes, the control of thrust amplitude by spanwise twisting of the fin, and the abrupt reversing of thrust. The tow speeds are low and close to the minimum induced velocity required for thrust onset by the flapping mechanism in the present propulsor—0 to 0.09 m/s, the fin chord 8, 250, and Reynolds number and shaft input power being 1 W. Time-averaged measurements show that thrust is more sensitive to pitch amplitude than to twisting during hovering, an effect that is reversed during slow towing due to the reduction in the spanwise variation of angle of attack. During towing, twist is more effective in the slosh mode than in the prop mode. Steady and quasi-steady thrust modeling is done to compare with prop- and slosh-mode measurements, respectively. The departures of the models are interpreted to mean that the beneficial effects of twist on the leading edge vortex (LEV) augment slosh forces and the rotational effects are detrimental to prop forces. We present simultaneous videography of fins during twisting and thrust reversal, and of thrust time trace as direct evidence of the relationship of cause and effect. Spanwise fin twisting is used to show that near-zero levels of thrust (0 to 1 N in steps of approximately 0.1 N) can be produced in both the slosh and prop modes and can be controlled merely by twisting the fins while keeping all other fin parameters unchanged. Transient-free reversal of the thrust direction has been achieved in the slosh mode while maintaining the same absolute value of thrust. However, thrust reversal in the prop mode is not transient free. This prop-mode transient is weaker due to the change in sign of the pitch angle but a change in the direction of the hub rotation produces a large spike and the reasons are discussed. Fine thrust control with individual fin hydrodynamics at the source that involves the lowest change in inertia is smoother. Smooth thrust reversibility is clearly identified as a unique property of flapping fin hydrodynamics. The mechanism overlap occurs because both fin modes have similar low transitional Reynolds numbers. Dynamical system models of unsteady hydrodynamics and control are shown to be similar suggesting that animal swimmers control vortex shedding ion-by-ion and animal-like motion control is theoretically possible with the proposed propulsor in the slosh mode but not in the prop mode.
关键词： hydrodynamics,oscillating propulsor,nonlinear control,force transient,Bioinspiration
更新于2025-09-16 10:30:52
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Hydrodynamic modeling and time-resolved imaging reflectometry of the ultrafast laser-induced ablation of a thin gold film
摘要： The ablation of thin metal films using ultrafast laser radiation represents a standard processing procedure in laser technology. However, looking closer to the resulting structures, the arising topology deviates strongly from the expected one. Ablation of thin gold films using ultrafast laser radiation with a Gaussian-shaped spatial intensity distribution results in flat topologies. By synergistically combining space and time-resolved reflectometry with expanded two-temperature hydrodynamic modeling, we explain the formation of bulging and rupture of the thin film-surface by the expansion of strongly stretched liquid material due to the induced rarefaction wave propagating towards the substrate. Also, the formation of a flat ablation structure is described by the interplay of two rarefaction waves, one propagating towards the substrate and the other one propagating towards the vacuum boundary, within the completely molten film. The simulated topology agrees excellent with the experimentally observed ablation structure. Besides, all simulated stages of excitation of the gold film, namely electron-phonon non-equilibrium, hydrodynamic expansion, and rupture, are confirmed by space and time-resolved pump-probe reflectometry.
关键词： Imaging reflectometry,Thin film ablation,Femtosecond laser radiation,Two temperature model hydrodynamics (TTMHD),Gold thin film,Ultrafast metrology
更新于2025-09-16 10:30:52
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High-Energy-Density Physics and Laser Technologies
摘要： This paper is devoted to the jubilee of I.M. Khalatnikov, the founder and the first director of the Landau Institute for Theoretical Physics of the Russian Academy of Sciences. I.M. Khalatnikov organized a first-class institute the studies at which cover a broad spectrum of research directions. The plasma and lasers department of the Institute conducts research on plasma physics problems, laser–matter interaction, questions pertaining to laser applications, and hydrodynamics problems. Much attention is given to solid-state physics with an emphasis on the behavior of matter in extreme conditions under intense laser irradiation. A number of new results are presented: the behavior of metals in two-temperature states (when the temperature of the electron subsystem of a metal is much greater than the temperature of the ion subsystem due to ultrafast laser heating); determining the boundaries of existence of a single-wave propagation mode of elastoplastic shock waves in ductile metal crystals; the formation of a laser torch from target materials and liquids under metal laser ablation of a metal into the surrounding liquid; the physical–mechanical consequences (melting, capillarity, recrystallization) of nonuniform (along the irradiated surface) energy dissipation caused by the interference of plasmon–polariton and laser electromagnetic fields.
关键词： laser–matter interaction,plasma physics,laser ablation,hydrodynamics,two-temperature states,plasmon–polariton,solid-state physics,high-energy-density physics,laser technologies,elastoplastic shock waves
更新于2025-09-12 10:27:22
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The study of laser cooling of TeH- anion in theoretical approach
摘要： For systems with extremely low accretion rate, such as Galactic Center Sgr A* and M87 galaxy, the ion collisional mean free path can be considerably larger than its Larmor radius. In this case, the gas pressure is anisotropic to magnetic ?eld lines. In this paper, we pay attention to how the properties of out?ow change with the strength of anisotropic pressure and the magnetic ?eld. We use an anisotropic viscosity to model the anisotropic pressure. We solve the two-dimensional magnetohydrodynamic (MHD) equations in spherical coordinates and assume that the accretion ?ow is radially self-similar. We ?nd that the work done by anisotropic pressure can heat the accretion ?ow. The gas temperature is heightened when anisotropic stress is included. The out?ow velocity increases with the enhancement of strength of the anisotropic force. The Bernoulli parameter does not change much when anisotropic pressure is involved. However, we ?nd that the energy ?ux of out?ow can be increased by a factor of 20 in the presence of anisotropic stress. We ?nd strong wind (the mass out?ow is about 70% of the mass in?ow rate) is formed when a relatively strong magnetic ?eld is present. Out?ows from an active galactic nucleus can interact with gas in its host galaxies. Our result predicts that out?ow feedback effects can be enhanced signi?cantly when anisotropic pressure and a relatively powerful magnetic ?eld is considered.
关键词： accretion discs,hydrodynamics,accretion,black hole physics
更新于2025-09-11 14:15:04
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Laser-driven strong shocks with infrared lasers at intensity of 10 <sup>16</sup> W/cm <sup>2</sup>
摘要： We present the results of an experiment on laser-driven shock waves performed at the Prague Asterix Laser system (PALS), where the fundamental frequency of the laser (1315 nm) is used to launch a strong shock in planar geometry. The experiment aims to characterize both shock waves and hot electrons generated at intensities of ’ 1016 W=cm2. It is shown that, in these interaction conditions, hydrodynamics is strongly impacted by noncollisional mechanisms, and the role of the hot electrons, generated by parametric instabilities, is essential in determining shock dynamics.
关键词： laser-driven shock waves,parametric instabilities,hot electrons,hydrodynamics
更新于2025-09-11 14:15:04
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Simulation of the temperature distribution and solidified bead in single-pass selective laser melting using a mesh-free method
摘要： The distribution of temperature and the formation of a solidified bead have considerable influence on single-pass selective laser melting (SLM). In this study, a transient three-dimensional numerical model is developed to simulate the evolution of the temperature field and the solidified bead by using smoothed-particle hydrodynamics, and the influences of processing parameters such as laser power, scanning speed, porosity, and thickness of the powder layer are studied and analyzed. The results show that the solidified bead forms as the powder material melts, and its shape changes from initially planar to a semicylindrical track because of the influence of the surface tension in the scanning process. Meanwhile, there is a discontinuous temperature distribution between the unmelted powder layer and the substrate material. Both the temperature distribution and the solidified bead deformation increase in the SLM process with the increase of the laser power and the porosity of the powder layer, but they both are apt to decrease with the increase of the scanning speed and the thickness of the powder layer. Experiments into the deformation distribution of the solidified bead and the dimensions of the molten pool are carried out under the same processing parameters, and the results are largely consistent with those from the simulation.
关键词： processing parameters,solidified bead,smoothed-particle hydrodynamics,temperature distribution,Selective laser melting
更新于2025-09-11 14:15:04