The dynamical progresses involved in ultra-short laser pulse ablation of face-centered cubic metals under stress confinement condition are described completely using molecular dynamics method. The laser beam absorptio...The dynamical progresses involved in ultra-short laser pulse ablation of face-centered cubic metals under stress confinement condition are described completely using molecular dynamics method. The laser beam absorption and thermal energy turning into kinetics energy of. atoms are taken into account to give a detailed picture of laser metal interaction. Superheating phenomenon is observed, and the phase change from solid to liquid is characterized by a destroyed atom configuration and a decreased number density. The steep velocity gradients are found in the systems of Cu and Ni after pulse in consequence of located heating and exponential decrease of fluences following the Lambert-Beer expression. The shock wave velocities are predicted to be about 5 000 m/s in Cu and 7 200 m/s in Ni. The higher ablation rates are obtained from simulations compared with experimental data as a result of a well-defined crystalline surface irradiated by a single pulse. Simulation results show that the main mechanisms of ablation are evaporation and thermoelastic stress due to located heating.展开更多
Based on the kinetic theoretical Vlasov-Poisson equation, a surface Coulomb explosion model of SiO2 material induced by ultra-short pulsed laser radiation is established. The non-equilibrium free electron distribution...Based on the kinetic theoretical Vlasov-Poisson equation, a surface Coulomb explosion model of SiO2 material induced by ultra-short pulsed laser radiation is established. The non-equilibrium free electron distribution resulting from the two mechanisms of multi-photon ionization and avalanche ionization is computed. A quantitative analysis is given to describe the Coulomb explosion induced by the self-consistent electric field, and the impact of the parameters of laser pulses on the surface ablation is also discussed. The results show that the electron relaxation time is not constant, but it is related to the microscopic state of the electrons, so the relaxation time approximation is not available on the femtosecond time scale. The ablation depths computed by the theoretical model are in good agreement with the experimental results in the range of pulse durations from 0 to 1 ps.展开更多
We develop a new synthetical model of high-power pulsed laser ablation,which considers the dynamicabsorptance,vaporization,and plasma shielding.And the corresponding heat conduction equations with the initial andbound...We develop a new synthetical model of high-power pulsed laser ablation,which considers the dynamicabsorptance,vaporization,and plasma shielding.And the corresponding heat conduction equations with the initial andboundary conditions are given.The numerical solutions are obtained under the reasonable technical parameter condi-tions by taking YBa_2Cu_3O_7 target for example.The space-dependence and time-dependence of temperature in targetat a certain laser fluence are presented,then,the transmitted intensity through plasma plume,space-dependence oftemperature and ablation rate for different laser fluences are significantly analyzed.As a result,the satisfactorily goodagreement between our numerical results and experimental results indicates that the influences of the dynamic absorp-tance,vaporization,and plasma shielding cannot be neglected.Taking all the three mechanisms above simultaneouslyinto account for the first time,we cause the present model to be more practical.展开更多
In order to further improve the propulsion performance of pulsed plasma thrusters for space micro propulsion,a novel laser ablation pulsed plasma thruster is proposed,which separated the laser ablation and electromagn...In order to further improve the propulsion performance of pulsed plasma thrusters for space micro propulsion,a novel laser ablation pulsed plasma thruster is proposed,which separated the laser ablation and electromagnetic acceleration.Optical emission spectroscopy is utilized to investigate the plasma characteristics in the thruster.The spectral lines at different times,positions and discharge intensities are experimentally recorded,and the plasma characteristics in the discharge channel are concluded through analyzing the variation of spectral lines.With the discharge energy of 24 J,laser energy of 0.6 J and the use of aluminum propellant,the specific impulse and thrust efficiency reach 6808 s and 70.6%,respectively.展开更多
This review provides a discussion of the current state of research on sp-carbon chains synthesized by pulsed laser ablation in liquid.In recent years,pulsed laser ablation in liquid(PLAL)has been widely employed for p...This review provides a discussion of the current state of research on sp-carbon chains synthesized by pulsed laser ablation in liquid.In recent years,pulsed laser ablation in liquid(PLAL)has been widely employed for polyynes synthesis thanks to its flexibility with varying laser parameters,solvents,and targets.This allows the control of sp-carbon chains properties as yield,length,termination and stability.Although many reviews related to PLAL have been published,a comprehensive work reporting the current status and advances related to the synthesis of sp-carbon chains by PLAL is still missing.Here we first review the principle of PLAL and the mechanisms of formation of sp-carbon chains.Then we discuss the role of laser fluence(i.e.energy density),solvent,and target for sp-carbon chains synthesis.Lastly,we report the progress related to the prolonged stability of sp-carbon chains by PLAL encapsulated in polymeric matrices.This review will be a helpful guide for researchers interested in synthesizing sp-carbon chains by PLAL.展开更多
The 2024 aluminum alloy is used extensively in the aircraft and aerospace industries because of its excellent mechanical properties.However,the weldability of 2024 aluminum alloy is generally low because it contains a...The 2024 aluminum alloy is used extensively in the aircraft and aerospace industries because of its excellent mechanical properties.However,the weldability of 2024 aluminum alloy is generally low because it contains a high number of solutes,such as copper(Cu),magnesium(Mg),and manganese(Mn),causing solidification cracking.If high speed welding of 2024 aluminum alloy without the use of filler is achieved,the applicability of 2024 aluminum alloys will expand.Grain refining is one of the methods used to prevent solidification cracking in weld metal,although it has never been achieved for high-speed laser welding of 2024 aluminum alloy without filler.Here,we propose a short-pulsed,laser-induced,grain-refining method during continuous wave laser welding without filler.Bead-on-plate welding was performed on a 2024-T3 aluminum alloy at a welding speed of 1 m min−1 with a single mode fiber laser at a wavelength of 1070 nm and power of 1 kW.Areas in and around the molten pool were irradiated with nanosecond laser pulses at a wavelength of 1064 nm,pulse width of 10 ns,and pulse energy of 430 mJ.The grain-refinement effect was confirmed when laser pulses were irradiated on the molten pool.The grain-refinement region was formed in a semicircular shape along the solid–liquid interface.Results of the vertical section indicate that the grain-refinement region reached a depth of 1 mm along the solid–liquid interface.The Vickers hardness test results demonstrated that the hardness increased as a result of grain refinement and that the progress of solidification cracking was suppressed in the grain refinement region.展开更多
TiO2 thin films were prepared on glass substrates using the PLD (Pulsed Laser Deposition) technique. In order to carry out the ablation process, a Nd:YAG laser was used emitting in 1064 nm wavelength at 10 Hz repetiti...TiO2 thin films were prepared on glass substrates using the PLD (Pulsed Laser Deposition) technique. In order to carry out the ablation process, a Nd:YAG laser was used emitting in 1064 nm wavelength at 10 Hz repetition rate, set up for operating in both single-pulse and multi-pulse regimes. A comparison of the deposition rate, the optical and morphological properties of the layers obtained from both ablation regimes was made, which showed that the multi-pulsed ablation produced layers with a higher surface quality and better optical properties.展开更多
A new technique to synthesize poly（diphenylsilylenemethylene） （PDPhSM） matrix nanocomposite thin films containing metal nanoparticles such as Ni, AI, Zn, and W produced by pulsed laser ablation has been developed....A new technique to synthesize poly（diphenylsilylenemethylene） （PDPhSM） matrix nanocomposite thin films containing metal nanoparticles such as Ni, AI, Zn, and W produced by pulsed laser ablation has been developed. First, 1,1,3,3-tetra- phenyl-1,3-disilacyclobutane （TPDC） films were deposited on 4 cm2 silicon substrates cut from c-Si wafers by conventional vacuum evaporation under a pressure of 4.0×10^-3 Pa; then metal nanoparticles were deposited onto the TPDC films by pulsed laser ablation; finally the TPDC films with metal nanoparticles were heated in an electric furnace in an air atmosphere at 553 K for 10 rain to induce ring-opening polymerization of TPDC. The results indicate that it is easy to synthesize metal/ PDPhSM nanocomposite thin films by pulsed laser ablation. The morphologies and size of metal nanoparticles are closely related to the kinds of metal. Also, the polymerization efficiency depends on the kinds of metal nanoparticles deposited on the TPDC monomer films by pulsed laser ablation. In addition, The laser ablated metal nanoparticles penetrate into the TPDC monomer films during pulsed laser ablation while the DC sputtered metal nanoparticles just lay on the surface of TPDC films.展开更多
High resolution spectral analysis of lithium plasma formed by single and double laser ablation has been undertaken to understand the plume-laser interaction, especially at the early stages of the plasma plume. In orde...High resolution spectral analysis of lithium plasma formed by single and double laser ablation has been undertaken to understand the plume-laser interaction, especially at the early stages of the plasma plume. In order to identify different atomic processes in evolving plasma, time resolved spectral emission studies at different inter-pulse delays have been performed for ionic and neutral lithium lines emitting from different levels. Along with the enhancement in emission intensity, a large line broadening and spectral shift, especially in the case of excited state transition Li I 610.3 nm have been observed in the presence of the second pulse. This broadening and shift gradually decrease with increasing time delay. Another interesting feature is the appearance of a multi-component structure in the ionic line at 548.4 nm and these components change conversely into a single structure at the later stages of the plasma. The multi-component structures are correlated with the presence of different velocity （temperature） distributions in non-LTE conditions. Atomic analyses by computing photon emissivity coefficients with an ADAS code have been used to identify the above processes.展开更多
To determine the nucleation region location of Si nano-crystal grains, pulsed laser ablation of Si target is performed in Ar gas of 10 Pa at room temperature with laser fluence of 4 J/cm2, the substrates are located h...To determine the nucleation region location of Si nano-crystal grains, pulsed laser ablation of Si target is performed in Ar gas of 10 Pa at room temperature with laser fluence of 4 J/cm2, the substrates are located horizontal under ablation spot with different vertical distance. Characteristics of deposited grains are described by scanning electron microscopy, Raman scattering and X-ray diffraction spectra, the results indicate that deposition position on substrates in a certain range is relative to target surface, which changes according to different vertical distance of substrates to ablation spot. Grain size increased?at first and then decreased with addition of lateral distances to target in the range, but the integral distribution rule was independent of position of substrates. Combining with hydrodynamics model, nucleation division model, thermokinetic equation and flat parabolic motion, spatial nucleation region location of grains is obtained through numerical calculations, which is 2.7 mm-43.2 mm to target surface along the plume axis.展开更多
In this study,a laser-assisted pulsed plasma thruster(LA-PPT)with a novel configuration is proposed as an electric propulsion thruster which separates laser ablation and electromagnetic acceleration.Owing to the uniqu...In this study,a laser-assisted pulsed plasma thruster(LA-PPT)with a novel configuration is proposed as an electric propulsion thruster which separates laser ablation and electromagnetic acceleration.Owing to the unique structure of the thruster,metals can also be used as propellants,and a higher specific impulse is expected.The ablation quality,morphology,and plume distribution of various metals(aluminium alloy,red copper,and carbon steel)with different laser energies were studied experimentally.The ablation morphology and plume distribution of red copper were more uniform,as compared to those of other metals,and the ablation quality was higher,indicating its greater suitability for LA-PPT.The plume generated by nanosecond laser ablation of aluminium alloy expanded faster,which indicated that the response time of the thruster with aluminium alloy as the propellant was shorter.In addition,when the background pressure was 0.005 Pa,an obvious plume splitting phenomenon was observed in the ablation plume of the pulsed laser irradiating aluminium alloy,which may significantly reduce the utilisation rate of the propellant.展开更多
This paper reports on the ablation process of a pure Ti solid target immersed in a C-enriched acetone solution, leading to the production of titanium carbide (TiC) and Ti-C core-shell nanostructures. The used route of...This paper reports on the ablation process of a pure Ti solid target immersed in a C-enriched acetone solution, leading to the production of titanium carbide (TiC) and Ti-C core-shell nanostructures. The used route of synthesis is generally called pulsed laser ablation in liquid (PLAL). The presence of carbon structures in the solution contributed to the carbon content in the produced Ti-based nanomaterials. The atomic composition of the produced nanostructures was analyzed using SEM-EDS, while TEM micrographs revealed the formation of spherical TiC and core-shell nanostructures ranging from 40 to 100 nm. The identification of atomic planes by HRTEM confirmed a 10 nm diameter C-shell with a graphite structure surrounding the Ti-core. Raman spectroscopy allowed for the identification of D and G peaks for graphite and a Raman signal at 380 and 600 cm<sup>−1</sup>, assigned to TiC. The results contribute to the state-of-the-art production of TiC and Ti-C core-shell nanostructures using the PLAL route.展开更多
New tungsten ion source is produced by using single and double-pulse laser ablation system. Combined collinear Nd：YAG laser beams（266＋1064 nm） are optimized to focus on the sample in air. Optimization of the exper...New tungsten ion source is produced by using single and double-pulse laser ablation system. Combined collinear Nd：YAG laser beams（266＋1064 nm） are optimized to focus on the sample in air. Optimization of the experimental parameters is achieved to enhance the signal-to-noise ratio of the emission spectra. The velocity distribution of the emitted plasma cloud is carefully measured. The influences of the potential difference between the bias electrodes, laser wavelength and intensity on the current signal are also studied. The results show that the increase in the tungsten ion velocity under the double-pulse lasers causes the output current signal to increase by about three folds. The electron density and temperature are calculated by using the Stark-broadened line profile of tungsten line and Boltzmann plot method of the upper energy levels, respectively. The signal intensity dependence of the tungsten ion angular distribution is also analyzed. The results indicate that the double-pulse laser ablation configuration is more potent technique for producing more metal ion source deposition, thin film formation, and activated plasma-facing component material.展开更多
We investigated the role of metal atomization and solvent decomposition into reductive species and carbon clusters in the phase formation of transition-metal carbides(TMCs;namely,Co_(3)C,Fe_(3)C,TiC,and MoC)by pulsed ...We investigated the role of metal atomization and solvent decomposition into reductive species and carbon clusters in the phase formation of transition-metal carbides(TMCs;namely,Co_(3)C,Fe_(3)C,TiC,and MoC)by pulsed laser ablation of Co,Fe,Ti,and Mo metals in acetone.The interaction between carbon s-p-orbitals and metal d-orbitals causes a redistribution of valence structure through charge transfer,leading to the formation of surface defects as observed by X-ray photoelectron spectroscopy.These defects influence the evolved TMCs,making them effective for hydrogen and oxygen evolution reactions(HER and OER)in an alkaline medium.Co_(3)C with more oxygen affinity promoted CoO(OH)intermediates,and the electrochemical surface oxidation to Co_(3)O_(4)was captured via in situ/operando electrochemical Raman probes,increasing the number of active sites for OER activity.MoC with more d-vacancies exhibits strong hydrogen binding,promoting HER kinetics,whereas Fe_(3)C and TiC with more defect states to trap charge carriers may hinder both OER and HER activities.The results show that the assembled membrane-less electrolyzer with Co_(3)C∥Co_(3)C and MoC∥MoC electrodes requires~2.01 and 1.99 V,respectively,to deliver a 10 mA cm−2 with excellent electrochemical and structural stability.In addition,the ascertained pulsed laser synthesis mechanism and unit-cell packing relations will open up sustainable pathways for obtaining highly stable electrocatalysts for electrolyzers.展开更多
Ultra-short laser pulses possess many advantages for materials processing.Ultrafast laser has a significantly low thermal effect on the areas surrounding the focal point;therefore,it is a promising tool for micro-and ...Ultra-short laser pulses possess many advantages for materials processing.Ultrafast laser has a significantly low thermal effect on the areas surrounding the focal point;therefore,it is a promising tool for micro-and submicro-sized precision processing.In addition,the nonlinear multiphoton absorption phenomenon of focused ultra-short pulses provides a promising method for the fabrication of various structures on transparent material,such as glass and transparent polymers.A laser direct writing process was applied in the fabrication of high-performance three-dimensional(3D)structured multilayer microsupercapacitors(MSCs)on polymer substrates exhibiting a peak specific capacitance of 42.6 mF·cm^-2 at a current density of 0.1 mA·cm^-12.Furthermore,a flexible smart sensor array on a polymer substrate was fabricated for multi-flavor detection.Different surface treatments such as gold plating,reducedgraphene oxide(rGO)coating,and polyaniline(PANI)coating were accomplished for different measurement units.By applying principal component analysis(PCA),this sensing system showed a promising result for flavor detection.In addition,two-dimensional(2D)periodic metal nanostructures inside 3D glass microfluidic channels were developed by all-femtosecond-laser processing for real-time surfaceenhanced Raman spectroscopy(SERS).The processing mechanisms included laser ablation,laser reduction,and laser-induced surface nano-engineering.These works demonstrate the attractive potential of ultra-short pulsed laser for surface precision manufacturing.展开更多
Glass welding by ultra-short pulsed(USP)lasers is a piece of technology that offers high strength joints with hermetic sealing.The joints are typically formed in glass that is transparent to the laser by exploiting no...Glass welding by ultra-short pulsed(USP)lasers is a piece of technology that offers high strength joints with hermetic sealing.The joints are typically formed in glass that is transparent to the laser by exploiting nonlinear absorption effects that occur under extreme conditions.Though the temperature reached during the process is on the order of a few 1000°C,the heat affected zone(HAZ)is confined to only tens of micrometers.It is this controlled confinement of the HAZ during the joining process that makes this technology so appealing to a multitude of applications because it allows the foregoing of a subsequent tempering step that is typically essential in other glass joining techniques,thus making it possible to effectively join highly heat sensitive components.In this work,we give an overview on the process,development and applications of glass welding by USP lasers.展开更多
The objective of this work was to investigate the possibility of taper angle correction in cutting of complex micro-mechanical contours using a TruMicro ultra-short pulse laser in combination with the SCANLAB precSYS ...The objective of this work was to investigate the possibility of taper angle correction in cutting of complex micro-mechanical contours using a TruMicro ultra-short pulse laser in combination with the SCANLAB precSYS micro machining sub system. In a first step, the influence of the process parameters on the kerftaper angle of metallic alloys was systematically investigated without beam inclination. A set of base parameters was derived for the subsequent investigations. In a second step, the kerftaper angle was controlled by static beam inclination. In a third step, the same optics was used in its dynamic precession mode to fabricate micro-mechanical components of complex contours with perpendicular 0~ taper angles. It was found that taper angle adjustments of up to 7.5~ are possible with the used setup for cutting applications. Taper angle control is possible both in the static beam inclination mode and in the dynamic precession mode. The static mode could be interesting for contours with sharp inner radii and for achieving faster cutting times similar to results with fixed optics, but would require excellent synchronization of beam inclination and axis motion. The dynamic precession mode would allow an easier integration of the optics into a laser machine but will result in longer cutting times and limitations with respect to achievable inner radii.展开更多
Thermal characteristics of tightly-contacted copper-gold double-layer thin film target under ablation of femtosec- ond laser pulses are investigated by using a two-temperature theoretical model. Numerical simulation s...Thermal characteristics of tightly-contacted copper-gold double-layer thin film target under ablation of femtosec- ond laser pulses are investigated by using a two-temperature theoretical model. Numerical simulation shows that electron heat flux varies significantly on the boundary of copper-gold film with different maximal electron temperature of 1.15 x 103 K at 5 ps after ablating laser pulse in gold and copper films, which can reach a balance around 12.6 ps and 8.2 ps for a single and double pulse ablation, respectively, and in the meantime, the lattice temperature difference crossing the gold-copper interface is only about 0.04×103 K at the same time scale. It is also found that electron-lattice heat relaxation time increases linearly with laser fluence in both single and double pulse ablation, and a sudden change of the relaxation time appears after the laser energy density exceeds the ablation threshold.展开更多
This paper focuses on the preparation of a new extended set of calibrations of cooling rate(fictive temperature)in fused silica determined by inelastic light scattering and its subsequent use to characterize the local...This paper focuses on the preparation of a new extended set of calibrations of cooling rate(fictive temperature)in fused silica determined by inelastic light scattering and its subsequent use to characterize the local cooling rate distribution in ultra-short pulsed(USP)laser modification.In order to determine the thermal history(e.g.cooling rate and fictive temperature)of fused silica,high-resolution inelastic light-scattering experiments(Raman and Brillouin spectroscopy)were investigated.Calibrations were performed and compared to the existing literature to quantify structural changes due to a change of fictive temperature.Compared to existing calibrations,this paper provides an extension to lower and higher cooling rates.Using this new set of calibrations,we characterized a USP laser modification in fused silica and calculated the local fictive temperature distribution.An equation relating the fictive temperature(Tf)to cooling rates is given.A maximum cooling rate of 3000 K min-1 in the glass transition region around 1200℃ was deduced from the Raman analysis.The Brillouin observations are sensitive to both the thermal history and the residual stress.By comparing the Raman and Brillouin observations,we extracted the local residual stress distribution with high spatial resolution.For the first time,combined Raman and Brillouin inelastic light scattering experiments show the local distribution of cooling rates and residual stresses(detailed behavior of the glass structure)in the interior and the surrounding of an USP laser modified zone.展开更多
Spatiotemporal shaping of ultrashort pulses is pivotal for various technologies,such as burst laser ablation and ultrafast imaging.However,the difficulty of pulse stretching to subnanosecond intervals and independent ...Spatiotemporal shaping of ultrashort pulses is pivotal for various technologies,such as burst laser ablation and ultrafast imaging.However,the difficulty of pulse stretching to subnanosecond intervals and independent control of the spatial profile for each pulse limit their advancement.We present a pulse manipulation technique for producing spectrally separated GHz burst pulses from a single ultrashort pulse,where each pulse is spatially shapable.We demonstrated the production of pulse trains at intervals of 0.1 to 3 ns in the 800-and 400-nm wavelength bands and applied them to ultrafast single-shot transmission spectroscopic imaging(4 Gfps)of laser ablation dynamics with two-color sequentially timed all-optical mapping photography.Furthermore,we demonstrated the production of pulse trains containing a shifted or dual-peak pulse as examples of individual spatial shaping of GHz burst pulses.Our proposed technique brings unprecedented spatiotemporal manipulation of GHz burst pulses,which can be useful for a wide range of laser applications.展开更多
基金the Ministerial Level Advanced Research Foundation (ABAQ440261)
文摘The dynamical progresses involved in ultra-short laser pulse ablation of face-centered cubic metals under stress confinement condition are described completely using molecular dynamics method. The laser beam absorption and thermal energy turning into kinetics energy of. atoms are taken into account to give a detailed picture of laser metal interaction. Superheating phenomenon is observed, and the phase change from solid to liquid is characterized by a destroyed atom configuration and a decreased number density. The steep velocity gradients are found in the systems of Cu and Ni after pulse in consequence of located heating and exponential decrease of fluences following the Lambert-Beer expression. The shock wave velocities are predicted to be about 5 000 m/s in Cu and 7 200 m/s in Ni. The higher ablation rates are obtained from simulations compared with experimental data as a result of a well-defined crystalline surface irradiated by a single pulse. Simulation results show that the main mechanisms of ablation are evaporation and thermoelastic stress due to located heating.
文摘Based on the kinetic theoretical Vlasov-Poisson equation, a surface Coulomb explosion model of SiO2 material induced by ultra-short pulsed laser radiation is established. The non-equilibrium free electron distribution resulting from the two mechanisms of multi-photon ionization and avalanche ionization is computed. A quantitative analysis is given to describe the Coulomb explosion induced by the self-consistent electric field, and the impact of the parameters of laser pulses on the surface ablation is also discussed. The results show that the electron relaxation time is not constant, but it is related to the microscopic state of the electrons, so the relaxation time approximation is not available on the femtosecond time scale. The ablation depths computed by the theoretical model are in good agreement with the experimental results in the range of pulse durations from 0 to 1 ps.
基金National Natural Science Foundation of China under Grant Nos.10675048 and 10604017the Natural Science Foundation of Hubei Province under Grant No.2001ABB099the Sunshine Foundation of Wuhan City under Grant No.20045006071-40
文摘We develop a new synthetical model of high-power pulsed laser ablation,which considers the dynamicabsorptance,vaporization,and plasma shielding.And the corresponding heat conduction equations with the initial andboundary conditions are given.The numerical solutions are obtained under the reasonable technical parameter condi-tions by taking YBa_2Cu_3O_7 target for example.The space-dependence and time-dependence of temperature in targetat a certain laser fluence are presented,then,the transmitted intensity through plasma plume,space-dependence oftemperature and ablation rate for different laser fluences are significantly analyzed.As a result,the satisfactorily goodagreement between our numerical results and experimental results indicates that the influences of the dynamic absorp-tance,vaporization,and plasma shielding cannot be neglected.Taking all the three mechanisms above simultaneouslyinto account for the first time,we cause the present model to be more practical.
基金National Natural Science Foundation of China for the financial assistance provided under the grant number 11772354.
文摘In order to further improve the propulsion performance of pulsed plasma thrusters for space micro propulsion,a novel laser ablation pulsed plasma thruster is proposed,which separated the laser ablation and electromagnetic acceleration.Optical emission spectroscopy is utilized to investigate the plasma characteristics in the thruster.The spectral lines at different times,positions and discharge intensities are experimentally recorded,and the plasma characteristics in the discharge channel are concluded through analyzing the variation of spectral lines.With the discharge energy of 24 J,laser energy of 0.6 J and the use of aluminum propellant,the specific impulse and thrust efficiency reach 6808 s and 70.6%,respectively.
基金funding from the European Research Council(ERC)under the European Union’s Horizon 2020 research and innovation program ERC Consolidator Grant(ERC Co G2016 Esp LORE grant agreement No.724610,website:www.esplore.polimi.it)
文摘This review provides a discussion of the current state of research on sp-carbon chains synthesized by pulsed laser ablation in liquid.In recent years,pulsed laser ablation in liquid(PLAL)has been widely employed for polyynes synthesis thanks to its flexibility with varying laser parameters,solvents,and targets.This allows the control of sp-carbon chains properties as yield,length,termination and stability.Although many reviews related to PLAL have been published,a comprehensive work reporting the current status and advances related to the synthesis of sp-carbon chains by PLAL is still missing.Here we first review the principle of PLAL and the mechanisms of formation of sp-carbon chains.Then we discuss the role of laser fluence(i.e.energy density),solvent,and target for sp-carbon chains synthesis.Lastly,we report the progress related to the prolonged stability of sp-carbon chains by PLAL encapsulated in polymeric matrices.This review will be a helpful guide for researchers interested in synthesizing sp-carbon chains by PLAL.
基金The authors would like to thank Mr Tetsuji Kuwabara of NAC Image Technology Inc.for support of high-speed photographingThis work was supported in part by MEXT Quantum Leap Flagship Program(MEXT Q-LEAP)Grant No.JPMXS0118068348,JSPS KAKENHI Grant Nos.JP16H04247,JP16K14417,and 19K22061This work was funded in part by ImPACT Program of Council for Science,Technology and Innovation(Cabinet Office,Government of Japan).
文摘The 2024 aluminum alloy is used extensively in the aircraft and aerospace industries because of its excellent mechanical properties.However,the weldability of 2024 aluminum alloy is generally low because it contains a high number of solutes,such as copper(Cu),magnesium(Mg),and manganese(Mn),causing solidification cracking.If high speed welding of 2024 aluminum alloy without the use of filler is achieved,the applicability of 2024 aluminum alloys will expand.Grain refining is one of the methods used to prevent solidification cracking in weld metal,although it has never been achieved for high-speed laser welding of 2024 aluminum alloy without filler.Here,we propose a short-pulsed,laser-induced,grain-refining method during continuous wave laser welding without filler.Bead-on-plate welding was performed on a 2024-T3 aluminum alloy at a welding speed of 1 m min−1 with a single mode fiber laser at a wavelength of 1070 nm and power of 1 kW.Areas in and around the molten pool were irradiated with nanosecond laser pulses at a wavelength of 1064 nm,pulse width of 10 ns,and pulse energy of 430 mJ.The grain-refinement effect was confirmed when laser pulses were irradiated on the molten pool.The grain-refinement region was formed in a semicircular shape along the solid–liquid interface.Results of the vertical section indicate that the grain-refinement region reached a depth of 1 mm along the solid–liquid interface.The Vickers hardness test results demonstrated that the hardness increased as a result of grain refinement and that the progress of solidification cracking was suppressed in the grain refinement region.
文摘TiO2 thin films were prepared on glass substrates using the PLD (Pulsed Laser Deposition) technique. In order to carry out the ablation process, a Nd:YAG laser was used emitting in 1064 nm wavelength at 10 Hz repetition rate, set up for operating in both single-pulse and multi-pulse regimes. A comparison of the deposition rate, the optical and morphological properties of the layers obtained from both ablation regimes was made, which showed that the multi-pulsed ablation produced layers with a higher surface quality and better optical properties.
基金Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)
文摘A new technique to synthesize poly（diphenylsilylenemethylene） （PDPhSM） matrix nanocomposite thin films containing metal nanoparticles such as Ni, AI, Zn, and W produced by pulsed laser ablation has been developed. First, 1,1,3,3-tetra- phenyl-1,3-disilacyclobutane （TPDC） films were deposited on 4 cm2 silicon substrates cut from c-Si wafers by conventional vacuum evaporation under a pressure of 4.0×10^-3 Pa; then metal nanoparticles were deposited onto the TPDC films by pulsed laser ablation; finally the TPDC films with metal nanoparticles were heated in an electric furnace in an air atmosphere at 553 K for 10 rain to induce ring-opening polymerization of TPDC. The results indicate that it is easy to synthesize metal/ PDPhSM nanocomposite thin films by pulsed laser ablation. The morphologies and size of metal nanoparticles are closely related to the kinds of metal. Also, the polymerization efficiency depends on the kinds of metal nanoparticles deposited on the TPDC monomer films by pulsed laser ablation. In addition, The laser ablated metal nanoparticles penetrate into the TPDC monomer films during pulsed laser ablation while the DC sputtered metal nanoparticles just lay on the surface of TPDC films.
文摘High resolution spectral analysis of lithium plasma formed by single and double laser ablation has been undertaken to understand the plume-laser interaction, especially at the early stages of the plasma plume. In order to identify different atomic processes in evolving plasma, time resolved spectral emission studies at different inter-pulse delays have been performed for ionic and neutral lithium lines emitting from different levels. Along with the enhancement in emission intensity, a large line broadening and spectral shift, especially in the case of excited state transition Li I 610.3 nm have been observed in the presence of the second pulse. This broadening and shift gradually decrease with increasing time delay. Another interesting feature is the appearance of a multi-component structure in the ionic line at 548.4 nm and these components change conversely into a single structure at the later stages of the plasma. The multi-component structures are correlated with the presence of different velocity （temperature） distributions in non-LTE conditions. Atomic analyses by computing photon emissivity coefficients with an ADAS code have been used to identify the above processes.
文摘To determine the nucleation region location of Si nano-crystal grains, pulsed laser ablation of Si target is performed in Ar gas of 10 Pa at room temperature with laser fluence of 4 J/cm2, the substrates are located horizontal under ablation spot with different vertical distance. Characteristics of deposited grains are described by scanning electron microscopy, Raman scattering and X-ray diffraction spectra, the results indicate that deposition position on substrates in a certain range is relative to target surface, which changes according to different vertical distance of substrates to ablation spot. Grain size increased?at first and then decreased with addition of lateral distances to target in the range, but the integral distribution rule was independent of position of substrates. Combining with hydrodynamics model, nucleation division model, thermokinetic equation and flat parabolic motion, spatial nucleation region location of grains is obtained through numerical calculations, which is 2.7 mm-43.2 mm to target surface along the plume axis.
基金supported by National Natural Science Foundation of China(No.11772354)。
文摘In this study,a laser-assisted pulsed plasma thruster(LA-PPT)with a novel configuration is proposed as an electric propulsion thruster which separates laser ablation and electromagnetic acceleration.Owing to the unique structure of the thruster,metals can also be used as propellants,and a higher specific impulse is expected.The ablation quality,morphology,and plume distribution of various metals(aluminium alloy,red copper,and carbon steel)with different laser energies were studied experimentally.The ablation morphology and plume distribution of red copper were more uniform,as compared to those of other metals,and the ablation quality was higher,indicating its greater suitability for LA-PPT.The plume generated by nanosecond laser ablation of aluminium alloy expanded faster,which indicated that the response time of the thruster with aluminium alloy as the propellant was shorter.In addition,when the background pressure was 0.005 Pa,an obvious plume splitting phenomenon was observed in the ablation plume of the pulsed laser irradiating aluminium alloy,which may significantly reduce the utilisation rate of the propellant.
文摘This paper reports on the ablation process of a pure Ti solid target immersed in a C-enriched acetone solution, leading to the production of titanium carbide (TiC) and Ti-C core-shell nanostructures. The used route of synthesis is generally called pulsed laser ablation in liquid (PLAL). The presence of carbon structures in the solution contributed to the carbon content in the produced Ti-based nanomaterials. The atomic composition of the produced nanostructures was analyzed using SEM-EDS, while TEM micrographs revealed the formation of spherical TiC and core-shell nanostructures ranging from 40 to 100 nm. The identification of atomic planes by HRTEM confirmed a 10 nm diameter C-shell with a graphite structure surrounding the Ti-core. Raman spectroscopy allowed for the identification of D and G peaks for graphite and a Raman signal at 380 and 600 cm<sup>−1</sup>, assigned to TiC. The results contribute to the state-of-the-art production of TiC and Ti-C core-shell nanostructures using the PLAL route.
文摘New tungsten ion source is produced by using single and double-pulse laser ablation system. Combined collinear Nd：YAG laser beams（266＋1064 nm） are optimized to focus on the sample in air. Optimization of the experimental parameters is achieved to enhance the signal-to-noise ratio of the emission spectra. The velocity distribution of the emitted plasma cloud is carefully measured. The influences of the potential difference between the bias electrodes, laser wavelength and intensity on the current signal are also studied. The results show that the increase in the tungsten ion velocity under the double-pulse lasers causes the output current signal to increase by about three folds. The electron density and temperature are calculated by using the Stark-broadened line profile of tungsten line and Boltzmann plot method of the upper energy levels, respectively. The signal intensity dependence of the tungsten ion angular distribution is also analyzed. The results indicate that the double-pulse laser ablation configuration is more potent technique for producing more metal ion source deposition, thin film formation, and activated plasma-facing component material.
基金National Research Foundation of Korea,Grant/Award Numbers:2019H1D3A1A01071209,2021R1I1A1A01060380,2022R1A2C2010686,2022R1A4A3033528Korea Basic Science Institute,Grant/Award Numbers:2019R1A6C1010042,2021R1A6C103A427。
文摘We investigated the role of metal atomization and solvent decomposition into reductive species and carbon clusters in the phase formation of transition-metal carbides(TMCs;namely,Co_(3)C,Fe_(3)C,TiC,and MoC)by pulsed laser ablation of Co,Fe,Ti,and Mo metals in acetone.The interaction between carbon s-p-orbitals and metal d-orbitals causes a redistribution of valence structure through charge transfer,leading to the formation of surface defects as observed by X-ray photoelectron spectroscopy.These defects influence the evolved TMCs,making them effective for hydrogen and oxygen evolution reactions(HER and OER)in an alkaline medium.Co_(3)C with more oxygen affinity promoted CoO(OH)intermediates,and the electrochemical surface oxidation to Co_(3)O_(4)was captured via in situ/operando electrochemical Raman probes,increasing the number of active sites for OER activity.MoC with more d-vacancies exhibits strong hydrogen binding,promoting HER kinetics,whereas Fe_(3)C and TiC with more defect states to trap charge carriers may hinder both OER and HER activities.The results show that the assembled membrane-less electrolyzer with Co_(3)C∥Co_(3)C and MoC∥MoC electrodes requires~2.01 and 1.99 V,respectively,to deliver a 10 mA cm−2 with excellent electrochemical and structural stability.In addition,the ascertained pulsed laser synthesis mechanism and unit-cell packing relations will open up sustainable pathways for obtaining highly stable electrocatalysts for electrolyzers.
基金the University of Tennessee Research Foundation and a grant from the National Natural Science Foundation of China(51575016).
文摘Ultra-short laser pulses possess many advantages for materials processing.Ultrafast laser has a significantly low thermal effect on the areas surrounding the focal point;therefore,it is a promising tool for micro-and submicro-sized precision processing.In addition,the nonlinear multiphoton absorption phenomenon of focused ultra-short pulses provides a promising method for the fabrication of various structures on transparent material,such as glass and transparent polymers.A laser direct writing process was applied in the fabrication of high-performance three-dimensional(3D)structured multilayer microsupercapacitors(MSCs)on polymer substrates exhibiting a peak specific capacitance of 42.6 mF·cm^-2 at a current density of 0.1 mA·cm^-12.Furthermore,a flexible smart sensor array on a polymer substrate was fabricated for multi-flavor detection.Different surface treatments such as gold plating,reducedgraphene oxide(rGO)coating,and polyaniline(PANI)coating were accomplished for different measurement units.By applying principal component analysis(PCA),this sensing system showed a promising result for flavor detection.In addition,two-dimensional(2D)periodic metal nanostructures inside 3D glass microfluidic channels were developed by all-femtosecond-laser processing for real-time surfaceenhanced Raman spectroscopy(SERS).The processing mechanisms included laser ablation,laser reduction,and laser-induced surface nano-engineering.These works demonstrate the attractive potential of ultra-short pulsed laser for surface precision manufacturing.
基金The authors gratefully acknowledge support by the Graduate School in Advanced Optical Technologies(SAOT)of the Friedrich–Alexander-University of Erlangen–Nürnberg,and the Bayerisches Laserzentrum GmbH.
文摘Glass welding by ultra-short pulsed(USP)lasers is a piece of technology that offers high strength joints with hermetic sealing.The joints are typically formed in glass that is transparent to the laser by exploiting nonlinear absorption effects that occur under extreme conditions.Though the temperature reached during the process is on the order of a few 1000°C,the heat affected zone(HAZ)is confined to only tens of micrometers.It is this controlled confinement of the HAZ during the joining process that makes this technology so appealing to a multitude of applications because it allows the foregoing of a subsequent tempering step that is typically essential in other glass joining techniques,thus making it possible to effectively join highly heat sensitive components.In this work,we give an overview on the process,development and applications of glass welding by USP lasers.
文摘The objective of this work was to investigate the possibility of taper angle correction in cutting of complex micro-mechanical contours using a TruMicro ultra-short pulse laser in combination with the SCANLAB precSYS micro machining sub system. In a first step, the influence of the process parameters on the kerftaper angle of metallic alloys was systematically investigated without beam inclination. A set of base parameters was derived for the subsequent investigations. In a second step, the kerftaper angle was controlled by static beam inclination. In a third step, the same optics was used in its dynamic precession mode to fabricate micro-mechanical components of complex contours with perpendicular 0~ taper angles. It was found that taper angle adjustments of up to 7.5~ are possible with the used setup for cutting applications. Taper angle control is possible both in the static beam inclination mode and in the dynamic precession mode. The static mode could be interesting for contours with sharp inner radii and for achieving faster cutting times similar to results with fixed optics, but would require excellent synchronization of beam inclination and axis motion. The dynamic precession mode would allow an easier integration of the optics into a laser machine but will result in longer cutting times and limitations with respect to achievable inner radii.
基金supported by the National Natural Science Foundation of China (Grant No. 60978014)the Natural Science Foundation of Jilin Province (Grant No. 20090523)the Educational Commission of Jilin Province (Grant No. [2008]297)
文摘Thermal characteristics of tightly-contacted copper-gold double-layer thin film target under ablation of femtosec- ond laser pulses are investigated by using a two-temperature theoretical model. Numerical simulation shows that electron heat flux varies significantly on the boundary of copper-gold film with different maximal electron temperature of 1.15 x 103 K at 5 ps after ablating laser pulse in gold and copper films, which can reach a balance around 12.6 ps and 8.2 ps for a single and double pulse ablation, respectively, and in the meantime, the lattice temperature difference crossing the gold-copper interface is only about 0.04×103 K at the same time scale. It is also found that electron-lattice heat relaxation time increases linearly with laser fluence in both single and double pulse ablation, and a sudden change of the relaxation time appears after the laser energy density exceeds the ablation threshold.
基金The authors gratefully acknowledge support by the Deutsche Forschungsgemeinschaft through the Grant Nos.Ho1691/8-1 I Li2713/4-1 | Schm2115/62-1,the Graduate School in Advanced Optical Technologies(SAOT)of the Friedrich-Alexander-Universitat Erlangen-Nurnberg and the QSIL GmbH Quarzschmelze Ilmenau.
文摘This paper focuses on the preparation of a new extended set of calibrations of cooling rate(fictive temperature)in fused silica determined by inelastic light scattering and its subsequent use to characterize the local cooling rate distribution in ultra-short pulsed(USP)laser modification.In order to determine the thermal history(e.g.cooling rate and fictive temperature)of fused silica,high-resolution inelastic light-scattering experiments(Raman and Brillouin spectroscopy)were investigated.Calibrations were performed and compared to the existing literature to quantify structural changes due to a change of fictive temperature.Compared to existing calibrations,this paper provides an extension to lower and higher cooling rates.Using this new set of calibrations,we characterized a USP laser modification in fused silica and calculated the local fictive temperature distribution.An equation relating the fictive temperature(Tf)to cooling rates is given.A maximum cooling rate of 3000 K min-1 in the glass transition region around 1200℃ was deduced from the Raman analysis.The Brillouin observations are sensitive to both the thermal history and the residual stress.By comparing the Raman and Brillouin observations,we extracted the local residual stress distribution with high spatial resolution.For the first time,combined Raman and Brillouin inelastic light scattering experiments show the local distribution of cooling rates and residual stresses(detailed behavior of the glass structure)in the interior and the surrounding of an USP laser modified zone.
基金supported by MEXT Quantum Leap Flagship Program (MEXT Q-LEAP) (Grant No.JPMXS0118067246)K.S.was supported by JST ACT-X (JPMJAX22K8).Y.I.and A.I.were partly supported by JST PRESTO (JPMJPR2003 and JPMJPR1902,respectively)K.N.was partly supported by JST FOREST (JPMJFR215C).
文摘Spatiotemporal shaping of ultrashort pulses is pivotal for various technologies,such as burst laser ablation and ultrafast imaging.However,the difficulty of pulse stretching to subnanosecond intervals and independent control of the spatial profile for each pulse limit their advancement.We present a pulse manipulation technique for producing spectrally separated GHz burst pulses from a single ultrashort pulse,where each pulse is spatially shapable.We demonstrated the production of pulse trains at intervals of 0.1 to 3 ns in the 800-and 400-nm wavelength bands and applied them to ultrafast single-shot transmission spectroscopic imaging(4 Gfps)of laser ablation dynamics with two-color sequentially timed all-optical mapping photography.Furthermore,we demonstrated the production of pulse trains containing a shifted or dual-peak pulse as examples of individual spatial shaping of GHz burst pulses.Our proposed technique brings unprecedented spatiotemporal manipulation of GHz burst pulses,which can be useful for a wide range of laser applications.
