A mid-infrared femtosecond pulse laser with a single cycle and high intensity is an ideal driving light source for generating isolated attosecond pulses. Due to current experimental limitations, it is difficult to dir...A mid-infrared femtosecond pulse laser with a single cycle and high intensity is an ideal driving light source for generating isolated attosecond pulses. Due to current experimental limitations, it is difficult to directly achieve this type of laser light source in the laboratory. In this paper, we obtain such an ideal light source by adding a Ti sapphire pulse to the combined pulse laser consisting of two mid-infrared pulses. Specifically, by combining the synthesized pulse consisting of 8 fs/1200 nm/1.62 × 10^(14)W cm^(-2)and 12 fs/1800 nm/2.71 × 10^(14)W cm^(-2)with an additional 8 fs/800 nm/1.26 × 10^(14)W cm^(-2)Ti sapphire pulse, the resulting electric field waveform is very close to that of a 1170 nm femtosecond pulse with an intensity of 1.4 × 10^(15)W cm^(-2), a single-cycle pulse width, and a carrier-envelope phase of 0.25π. Numerical simulations show that both cases produce high-order harmonic emission spectra with broadband supercontinuum spectra, however, the bandwidth of the supercontinuum spectra and the harmonic intensities in the synthesized pulses are significantly better than those in the single1170 nm pulse. After inverse Fourier transform, we obtain 66 as a high-intensity isolated attosecond pulse, whose intensity is five orders of magnitude higher than that of a monochromatic field. Here, the phase differences between three combined pulse lasers have little effect on the numerical simulation results when they vary in the range of 0.3π.展开更多
Pulse laser welding of 0.6 mm-thick AA5052-H32 was performed to determine the optimum set of parameters including laser pulse current,pulse frequency and pulse duration that meets the AWS D17.1 specifications for aero...Pulse laser welding of 0.6 mm-thick AA5052-H32 was performed to determine the optimum set of parameters including laser pulse current,pulse frequency and pulse duration that meets the AWS D17.1 specifications for aerospace industry.The microstructure and mechanical properties of the weldments were also investigated.Relationships between the parameters and weld bead geometry were found.High quality weld joints without solidification crack that met AWS D17.1 requirements were obtained at(I)high pulse energy(25 J)and high average peak power(4.2 kW)and(II)low pulse energy(17.6 J)and low average peak power(2.8 kW).The weld joint formed at lower heat energy input exhibited finer dendritic grain structure.Mg vapourisation and hard phase compound(Al0.5Fe3Si0.5)formation decreased in the weld joint formed at lower heat energy input.Consequently,the tensile strength of the weldment formed at lower heat energy input(168 MPa)is by a factor of 1.15 higher but showed^29%decrease in hardness(111 HV0.1)at the joint when being compared with the weldment formed at higher heat energy input.Appropriate parameters selection is critical to obtaining 0.6 mm-thick AA5052-H32 pulse laser weld joints that meet AWS D17.1 requirements for aircraft structures.展开更多
Porosity is a challenging issue in additive manufacturing and is detrimental to the quality of the additively manufactured products.In this study,a real-time porosity reduction technique was developed by incorporating...Porosity is a challenging issue in additive manufacturing and is detrimental to the quality of the additively manufactured products.In this study,a real-time porosity reduction technique was developed by incorporating a pulse laser into a laser metal powder directed energy deposition(DED)system.The incorporated pulse laser can accelerate fluid flow within the melt pool and facilitate the escape of pores before complete solidification.It achieves this real-time porosity reduction by inducing accelerated and turbulent Marangoni flow,ultrasonic waves,and shock waves into the melt pool.The uniqueness and advantages of the proposed technique include the following:(1)For a laser metal powder DED process,this study proposed a noncontact,nondestructive,and real-time porosity reduction technique at the melt pool level.(2)It was experimentally and numerically validated that the developed technique did not alter the geometry and the grain structure of the manufactured Ti-6Al-4V samples.(3)Because the porosity reduction is accomplished at the melt pool level,its application is not limited by the size,shape,or complexity of the printing target.(4)The developed technique can be readily incorporated into the existing DED systems without any modification of the original tool-path design.The experimental results showed that the pore volume fraction decreased from 0.132%to 0.005%,no pores larger than 6×10^(4)μm^(3) were observed,and a 91%reduction in the total pore number was achieved when the pulse laser energy reached 11.5 mJ.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
The heteroepitaxial growth of multilayer Cu/Pd（100） thin film via pulse laser deposition （PLD） at room temperature is simulated by using kinetic Monte Carlo （KMC） method with realistic physical parameters. The e...The heteroepitaxial growth of multilayer Cu/Pd（100） thin film via pulse laser deposition （PLD） at room temperature is simulated by using kinetic Monte Carlo （KMC） method with realistic physical parameters. The effects of mass transport between interlayers, edge diffusion of adatoms along the islands and instantaneous deposition are considered in the simulation model, Emphasis is placed on revealing the details of multilayer Cu/Pd（100） thin film growth and estimating the Ehrlich-Schwoebel （ES） barrier. It is shown that the instantaneous deposition in the PLD growth gives rise to the layer-by-layer growth mode, persisting up to about 9 monolayers （ML） of Cu/Pd（100）. The ES barriers of 0.08 ± 0.01 eV is estimated by comparing the KMC simulation results with the real scanning tunnelling microscopy （STM） measurements,展开更多
The pulsed laser deposition(PLD)technology was used to effectively create conductive nano and micro hafnium oxide with great purity and transparency for(HfO_(2))nanofilms.In many optoelectronics devices and their appl...The pulsed laser deposition(PLD)technology was used to effectively create conductive nano and micro hafnium oxide with great purity and transparency for(HfO_(2))nanofilms.In many optoelectronics devices and their applications,the presence of a high dielectric substance like a nano HfO2,between the metal contacts and the substrates was critical.We used the Pulsed Laser Deposition method to fabricate an Al/HfO_(2)/p-Si Schottky barrier diode where the nanostructured HfO2 films as an intermediate layer and varied substrate temperatures.The optical result reveals a high degree of transparency(93%).The optical bandgap of deposited HfO2 films was observed to vary between 4.9 and 5.3 eV,with a value of roughly 5.3 eV at the optimal preparation condition.The morphology of the surface shows a high homogeneous nano structure with the average values of the roughness about(0.3 nm).With regard to substrate temperature,the produced factor ideality for fabricated diode was determined to be lowering and the associated values of the barrier height rose based on I-Vcharacterization.With regard to substrate temperature,the produced factor ideality for fabricated diode was determined to be lowering and the associated values of the barrier height rose based on I-V characterization.The diode manufactured at 600℃,in particular,had a higher ideality factor value(n=3.2).展开更多
It has been recently shown that inhomogeneity of a semiconductor heterostructure leads to increasing of sharpness of diffusion-junction and implanted-junction rectifiers,which are formed in the semiconductor heterostr...It has been recently shown that inhomogeneity of a semiconductor heterostructure leads to increasing of sharpness of diffusion-junction and implanted-junction rectifiers,which are formed in the semiconductor heterostructure.It has been also shown that together with increasing of the sharpness,homogeneity of impurity distribution in doped area increases.The both effect could be increased by formation of an inhomogeneous distribution of temperature(for example,by laser annealing).Some conditions on correlation between inhomogeneities of the semiconductor heterostructure and temperature distribution have been considered.Annealing time has been optimized for pulse laser annealing.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
ZnNiO thin films with different contents of Ni(0-10 at.%) were fabricated on quartz and Si(100) substrates by pulsed laser deposition(PLD).We measured the samples by X-ray diffraction(XRD),field-emission scanning elec...ZnNiO thin films with different contents of Ni(0-10 at.%) were fabricated on quartz and Si(100) substrates by pulsed laser deposition(PLD).We measured the samples by X-ray diffraction(XRD),field-emission scanning electron microscope(FE-SEM),X-ray photoelectron spectroscopy(XPS),ultraviolet-visible spectrometer(UV-VIS),and Hall testing.When the Ni contents were below 3 at.%,partial Zn2+ ions were replaced by the Ni2+ ions without forming any other phases,which enhanced the conductivity of the film.When the Ni contents were above 3 at.%,Ni ions were at the interstitial sites,and Ni-related clusters and defects were able to emerge in the films,resulting in a worsening of electrical and optical properties.A ferromagnetic hysteresis with a coercive force of approximately 30 Oe was observed in the ZnNiO film with a Ni content of 3 at.% at room temperature.展开更多
Irradiating hard rocks by a high-power laser can reduce localized hardness in the rocks;however,continuous lasers produce a large amount of melt that inhibits further heat absorption.Pulsed lasers allow rocks to absor...Irradiating hard rocks by a high-power laser can reduce localized hardness in the rocks;however,continuous lasers produce a large amount of melt that inhibits further heat absorption.Pulsed lasers allow rocks to absorb and dissipate energy and avoid melt formation.In this study,200 W nanosecond pulsed laser was used to irradiate granite.The effects of laser parameters on the thermal cracking morphology,temperature field,warming pattern,and Leeb hardness of the granite surface were analyzed.The optimal laser parameters for softening granite were determined by performing objective optimization in MATLAB using granite's melting point as the reference.Nanoindentation techniques were employed to assess the softening characteristics of the granite surface along the longitudinal direction.The results showed that three main forms of thermal damage occurred on the granite surface:oxidative decomposition,spalling,and melting.The damage state was affected by the average laser power,with the pulse width and repetition frequency affecting surface damage differently.Appropriate laser parameters effectively controlled the melt damage on the granite surface,and irradiation with nanosecond pulsed lasers effectively reduced surface hardness.However,excessive power can generate large amounts of hard melts and weaken the softening effect.展开更多
BaFe_(12)O_(19)(BaM)thin films with thicknesses ranging from 15 nm–200 nm were deposited on Al_(2)O_(3)(0001)substrates by pulsed laser deposition(PLD).X-ray diffraction patterns show that a buffer layer with a thick...BaFe_(12)O_(19)(BaM)thin films with thicknesses ranging from 15 nm–200 nm were deposited on Al_(2)O_(3)(0001)substrates by pulsed laser deposition(PLD).X-ray diffraction patterns show that a buffer layer with a thickness of nearly 60 nm forms on the substrate,and then a c-axis perpendicularly oriented Ba M thin film grows on the buffer layer.Atomic force microscopy results indicate that the Ba M thin film exhibits a spiral island growth mode on the buffer layer.Magnetic hysteresis loop results confirm that the buffer layer exhibits no significant magnetic anisotropy,while the Ba M thin film exhibits perpendicular magnetic anisotropy.The out-of-plane coercivity decreases with increasing Ba M thin-film thickness due to the combined effect of grain size growth and lattice strain relaxation.The 200 nm thick film exhibits optimum magnetic properties with M_(s)=319 emu/cm^(3) and H_(c)=1546 Oe.展开更多
Understanding the complex plasma dynamics in ultra-intense relativistic laser-solid interactions is of fundamental importance for applications of laser-plasma-based particle accelerators,the creation of high-energy-de...Understanding the complex plasma dynamics in ultra-intense relativistic laser-solid interactions is of fundamental importance for applications of laser-plasma-based particle accelerators,the creation of high-energy-density matter,understanding planetary science,and laser-driven fusion energy.However,experimental efforts in this regime have been limited by the lack of accessibility of over-critical densities and the poor spatiotemporal resolution of conventional diagnostics.Over the last decade,the advent of femtosecond brilliant hard X-ray free-electron lasers(XFELs)has opened new horizons to overcome these limitations.Here,for the first time,we present full-scale spatiotemporal measurements of solid-density plasma dynamics,including preplasma generation with tens of nanometer scale length driven by the leading edge of a relativistic laser pulse,ultrafast heating and ionization at the main pulse arrival,the laser-driven blast wave,and transient surface return current-induced compression dynamics up to hundreds of picoseconds after interaction.These observations are enabled by utilizing a novel combination of advanced X-ray diagnostics including small-angle X-ray scattering,resonant X-ray emission spectroscopy,and propagation-based X-ray phase-contrast imaging simultaneously at the European XFEL-HED beamline station.展开更多
Pulsed laser deposition(PLD),as an advanced synthesis technology with unparalleled control over thin films,has evolved into a universal platform for optoelectronic materials engineering.Its unique advantages including...Pulsed laser deposition(PLD),as an advanced synthesis technology with unparalleled control over thin films,has evolved into a universal platform for optoelectronic materials engineering.Its unique advantages including precise stoichiometric transfer,heterogeneous structure preparation and in-situ monitoring enable the design of opto-electrocatalysts with controllable active sites.Traditional methods struggle to pinpoint active sites in hydrogen technologies such as fuel cells and water electrolysis,impeding catalyst customization and mechanistic understanding.Nevertheless,PLD remains underused here despite its outstanding performances in targeted photo-assisted electrocatalysts design.This review systematically explores the breakthrough achievements and provides detailed insights into photo-enhanced water electrolysis and fuel cells based on PLD.Beginning with the fundamentals of epitaxial film growth and film classification,particularly emphasis the related in situ optical analysis techniques.It subsequently highlights recent advances in electro-oxidation and reduction reactions of H_(2)and O_(2),demonstrating the control capabilities of PLD in precisely correlating the structure and activity at the atomic level.Finally,the review concludes by proposing scalable fabrication strategies and performance optimization frameworks to bridge fundamental insights with industrial-scale optoelectronic integration systems.展开更多
We demonstrate a high-peak-power master oscillator power amplifier burst-mode laser system that generates microsecond burst duration pulses at 355 nm with a GHz-adjustable intra-burst pulse frequency.In the fiber seed...We demonstrate a high-peak-power master oscillator power amplifier burst-mode laser system that generates microsecond burst duration pulses at 355 nm with a GHz-adjustable intra-burst pulse frequency.In the fiber seed,a highbandwidth electro-optic modulator is employed to modulate a continuous-wave(CW)laser into a pulse train at GHz frequency.To acquire a microsecond rectangular burst pulse envelope,two acousto-optic modulators are used to chop the CW pulse train and generate a pre-compensation burst envelope.A three-stage neodymium-doped yttrium aluminum garnet amplifier boosts the burst-mode fiber seed’s burst energy of 1.65 J at 1064 nm.To achieve a high-power ultraviolet(UV)burst-mode laser,sum frequency generation in a LiB_(3)O_(5)crystal is employed to convert the wavelength,achieving over 300 kW of peak power at 1.15μs/10 Hz.The intra-burst pulse frequency of the UV burst laser can be adjustable from 1 to 10 GHz with a sinusoidal waveform.To the best of our knowledge,this paper represents the highest reported microsecond UV burst-mode laser in terms of output energy and peak power with the GHz-adjustable intra-burst frequency.The high-power microsecond UV burst-mode pulse laser can be directly used as a light-driven source in large-bandwidth/high-power microwave photonic systems,providing a long pulse width and high peak power laser while significantly improving the system’s multi-parameter adjustment capability and adaptability.展开更多
The development of highly active and cost-effective catalysts for the full pH range of the hydrogen evolution reaction(HER)to meet the industrial application demands is an urgent challenge.In this work,the performance...The development of highly active and cost-effective catalysts for the full pH range of the hydrogen evolution reaction(HER)to meet the industrial application demands is an urgent challenge.In this work,the performance and structure–activityrelationships of CuIr alloys prepared by the pulsed laser ablation in liquid technique as full pH range HER catalysts wereinvestigated.Results indicated that Ir is doped into the Cu matrix as single atoms in CuIr-0.1,and CuIr-0.1 single-atom alloys(SAAs)exhibit superior HER performance and stability across the full pH range,with overpotentials of 135,203,and 172 mVat the current density of 10 mA/cm^(2)in acidic,neutral,and alkaline electrolytes,respectively.The enhanced performance ofCuIr-0.1 SAAs can be attributed to the abundant active sites and accelerated reaction kinetics brought about by the electroniceffects.This work successfully alloyed two immiscible metals to improve the catalytic performance,providing an avenue forthe development of highly efficient and versatile HER catalysts for industrial applications.展开更多
Type-II Dirac semimetal PtTe2is a promising candidate for various electronic device applications due to its high carrier mobility,high conductivity,and air stability.In this work,we report on the growth of large-scale...Type-II Dirac semimetal PtTe2is a promising candidate for various electronic device applications due to its high carrier mobility,high conductivity,and air stability.In this work,we report on the growth of large-scale PtTe_(2)films by the pulsed laser deposition(PLD)and the comparison of the magnetotransport properties with the PtTe2films grown by the chemical vapor deposition(CVD).The low-temperature Hall curves of the PLD-grown films exhibit a linear behavior,in contrast with the nonlinear characteristic of the Hall behavior observed in CVD-grown films,in which a defect gradient is introduced.Meanwhile,both PtTe2films show weak antilocalization at low temperatures,which is attributed to the strong spin–orbit coupling.展开更多
Avoiding crystallization while maintaining the original microstructure and mechanical properties of the material are long-term goals of laser welding of Zr-based bulk metallic glass(BMG).In this paper,the effect of pu...Avoiding crystallization while maintaining the original microstructure and mechanical properties of the material are long-term goals of laser welding of Zr-based bulk metallic glass(BMG).In this paper,the effect of pulsed laser welding parameters on the microstructure,crystallization degree,and mechanical properties of Zr57Nb5Cu15.4Ni12.6Al10 BMG is investigated.Non-crystallized welding forming of a zirconium-based amorphous alloy is achieved by optimizing the process parameters of pulsed laser welding.The crystallization degree of Zr-based BMG is mainly determined by the welding speed and power.The welding depth and crystallization area fraction increase with an increase in the effective peak power density.The optimized welding process can effectively reduce the heat accumulation of the weld,thus avoiding crystallization.The flexural strength of the weld can be maintained at 96.5%of the matrix.展开更多
We propose an all-optical,single-laser-pulse scheme for generating a dense relativistic strongly magnetized electron-positron pair plasma.The scheme involves the interaction of an extremely intense(I■10^(24) W/cm^(2)...We propose an all-optical,single-laser-pulse scheme for generating a dense relativistic strongly magnetized electron-positron pair plasma.The scheme involves the interaction of an extremely intense(I■10^(24) W/cm^(2))circularly polarized laser pulse with a solid-density target containing a conical cavity.Through full-scale three-dimensional particle-in-cell simulations that account for quantum electrodynamic effects,it is shown that this interaction results in two significant outcomes:first,the generation of quasi-static magnetic fields reaching tens of gigagauss,and,second,the production of large quantities of electron-positron pairs(up to 10^(13))via the Breit-Wheeler process.The e^(-)e^(+)plasma becomes trapped in the magnetic field and remains confined in a small volume for hundreds of femtoseconds,far exceeding the laser timescale.The dependence of pair plasma parameters,as well as the efficiency of plasma production and confinement,is discussed in relation to the properties of the laser pulse and the target.Realizing this scheme experimentally would enable the investigation of physical processes relevant to extreme astrophysical environments.展开更多
A singlet diatomic molecule naturally carries doubly degenerate ±Λ states when the projection of the total electronic angular momentum onto the internuclear axis is nonzero. These doubly degenerate states contri...A singlet diatomic molecule naturally carries doubly degenerate ±Λ states when the projection of the total electronic angular momentum onto the internuclear axis is nonzero. These doubly degenerate states contribute equally in conventional measurements and are thus treated the same in corresponding simulations. In this study, we demonstrate that in resonant excitation by intense laser pulses, the doubly degenerate ±Λ states must be clearly identified. This is exemplified in the X^(1)Σ → A^(1)Π transition of CO molecules. This distinction becomes especially important in the case of circularly polarized radiation. We attribute this phenomenon to the interference of electron-rotational pathways in the strong-field coupled transition with the ±Λ-state of the excited Π state. This research sheds light on the fundamental aspects of intense laser-molecule interactions when extending conventional theories.展开更多
The generation and reconnection of magneticflux ropes in a plasma irradiated by two Laguerre–Gaussian laser pulses with different frequen-cies and opposite topological charges are investigated numerically by particle-...The generation and reconnection of magneticflux ropes in a plasma irradiated by two Laguerre–Gaussian laser pulses with different frequen-cies and opposite topological charges are investigated numerically by particle-in-cell simulations.It is shown that twisted plasma currents and hence magneticflux ropes can be effectively generated as long as the laser frequency difference matches the electron plasma frequency.More importantly,subsequent reconnection of magneticflux ropes can occur.Typical signatures of magnetic reconnection,such as magnetic island formation and plasma heating,are identified in the reconnection of magneticflux ropes.Notably,it is found that a strong axial magneticfield can be generated on the axis,owing to the azimuthal current induced during the reconnection of the ropes.This indicates that in the reconnection of magneticflux ropes,the energy can be transferred not only from the magneticfield to the plasma but also from the plasma current back to the magneticfield.This work opens a new avenue to the study of magneticflux ropes,which helps in understanding magnetic topology changes,and resultant magnetic energy dissipation,plasma heating,and particle acceleration found in solarflares,and magnetic confinement fusion devices.展开更多
基金supported by the Natural Science Foundation of Jilin Province under Grant No. 20220101028JC。
文摘A mid-infrared femtosecond pulse laser with a single cycle and high intensity is an ideal driving light source for generating isolated attosecond pulses. Due to current experimental limitations, it is difficult to directly achieve this type of laser light source in the laboratory. In this paper, we obtain such an ideal light source by adding a Ti sapphire pulse to the combined pulse laser consisting of two mid-infrared pulses. Specifically, by combining the synthesized pulse consisting of 8 fs/1200 nm/1.62 × 10^(14)W cm^(-2)and 12 fs/1800 nm/2.71 × 10^(14)W cm^(-2)with an additional 8 fs/800 nm/1.26 × 10^(14)W cm^(-2)Ti sapphire pulse, the resulting electric field waveform is very close to that of a 1170 nm femtosecond pulse with an intensity of 1.4 × 10^(15)W cm^(-2), a single-cycle pulse width, and a carrier-envelope phase of 0.25π. Numerical simulations show that both cases produce high-order harmonic emission spectra with broadband supercontinuum spectra, however, the bandwidth of the supercontinuum spectra and the harmonic intensities in the synthesized pulses are significantly better than those in the single1170 nm pulse. After inverse Fourier transform, we obtain 66 as a high-intensity isolated attosecond pulse, whose intensity is five orders of magnitude higher than that of a monochromatic field. Here, the phase differences between three combined pulse lasers have little effect on the numerical simulation results when they vary in the range of 0.3π.
基金the funding (UniversityIndustry Engagement Grant)support provided by the Universiti Sains Malaysia under the Teaching Fellowship Scheme
文摘Pulse laser welding of 0.6 mm-thick AA5052-H32 was performed to determine the optimum set of parameters including laser pulse current,pulse frequency and pulse duration that meets the AWS D17.1 specifications for aerospace industry.The microstructure and mechanical properties of the weldments were also investigated.Relationships between the parameters and weld bead geometry were found.High quality weld joints without solidification crack that met AWS D17.1 requirements were obtained at(I)high pulse energy(25 J)and high average peak power(4.2 kW)and(II)low pulse energy(17.6 J)and low average peak power(2.8 kW).The weld joint formed at lower heat energy input exhibited finer dendritic grain structure.Mg vapourisation and hard phase compound(Al0.5Fe3Si0.5)formation decreased in the weld joint formed at lower heat energy input.Consequently,the tensile strength of the weldment formed at lower heat energy input(168 MPa)is by a factor of 1.15 higher but showed^29%decrease in hardness(111 HV0.1)at the joint when being compared with the weldment formed at higher heat energy input.Appropriate parameters selection is critical to obtaining 0.6 mm-thick AA5052-H32 pulse laser weld joints that meet AWS D17.1 requirements for aircraft structures.
基金supported by a National Research Foundation of Korea(NRF)grant funded by the Korea government(MSIT)[Grant No.2019R1A3B3067987]supported by SQ Engineering during his stay at KAIST。
文摘Porosity is a challenging issue in additive manufacturing and is detrimental to the quality of the additively manufactured products.In this study,a real-time porosity reduction technique was developed by incorporating a pulse laser into a laser metal powder directed energy deposition(DED)system.The incorporated pulse laser can accelerate fluid flow within the melt pool and facilitate the escape of pores before complete solidification.It achieves this real-time porosity reduction by inducing accelerated and turbulent Marangoni flow,ultrasonic waves,and shock waves into the melt pool.The uniqueness and advantages of the proposed technique include the following:(1)For a laser metal powder DED process,this study proposed a noncontact,nondestructive,and real-time porosity reduction technique at the melt pool level.(2)It was experimentally and numerically validated that the developed technique did not alter the geometry and the grain structure of the manufactured Ti-6Al-4V samples.(3)Because the porosity reduction is accomplished at the melt pool level,its application is not limited by the size,shape,or complexity of the printing target.(4)The developed technique can be readily incorporated into the existing DED systems without any modification of the original tool-path design.The experimental results showed that the pore volume fraction decreased from 0.132%to 0.005%,no pores larger than 6×10^(4)μm^(3) were observed,and a 91%reduction in the total pore number was achieved when the pulse laser energy reached 11.5 mJ.
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Project supported by the State Key Development Program for Basic Research of China （Grant No 2006CB708612） and Natural Science Foundation for Young Scientists of Zhejiang Province, China （Grant No RC02069）.Acknowledgment We would like to thank Dr Ling-wang Wang of the Computational Research Division at the Lawrence Berkeley National Lab and Dr Xiangrong Ye of Department of Material Science and Chemical Engineering, University of California at San Diego for helpful discussion.
文摘The heteroepitaxial growth of multilayer Cu/Pd（100） thin film via pulse laser deposition （PLD） at room temperature is simulated by using kinetic Monte Carlo （KMC） method with realistic physical parameters. The effects of mass transport between interlayers, edge diffusion of adatoms along the islands and instantaneous deposition are considered in the simulation model, Emphasis is placed on revealing the details of multilayer Cu/Pd（100） thin film growth and estimating the Ehrlich-Schwoebel （ES） barrier. It is shown that the instantaneous deposition in the PLD growth gives rise to the layer-by-layer growth mode, persisting up to about 9 monolayers （ML） of Cu/Pd（100）. The ES barriers of 0.08 ± 0.01 eV is estimated by comparing the KMC simulation results with the real scanning tunnelling microscopy （STM） measurements,
文摘The pulsed laser deposition(PLD)technology was used to effectively create conductive nano and micro hafnium oxide with great purity and transparency for(HfO_(2))nanofilms.In many optoelectronics devices and their applications,the presence of a high dielectric substance like a nano HfO2,between the metal contacts and the substrates was critical.We used the Pulsed Laser Deposition method to fabricate an Al/HfO_(2)/p-Si Schottky barrier diode where the nanostructured HfO2 films as an intermediate layer and varied substrate temperatures.The optical result reveals a high degree of transparency(93%).The optical bandgap of deposited HfO2 films was observed to vary between 4.9 and 5.3 eV,with a value of roughly 5.3 eV at the optimal preparation condition.The morphology of the surface shows a high homogeneous nano structure with the average values of the roughness about(0.3 nm).With regard to substrate temperature,the produced factor ideality for fabricated diode was determined to be lowering and the associated values of the barrier height rose based on I-Vcharacterization.With regard to substrate temperature,the produced factor ideality for fabricated diode was determined to be lowering and the associated values of the barrier height rose based on I-V characterization.The diode manufactured at 600℃,in particular,had a higher ideality factor value(n=3.2).
基金supported by grant of President of Russia (project № MK-548.2010.2)
文摘It has been recently shown that inhomogeneity of a semiconductor heterostructure leads to increasing of sharpness of diffusion-junction and implanted-junction rectifiers,which are formed in the semiconductor heterostructure.It has been also shown that together with increasing of the sharpness,homogeneity of impurity distribution in doped area increases.The both effect could be increased by formation of an inhomogeneous distribution of temperature(for example,by laser annealing).Some conditions on correlation between inhomogeneities of the semiconductor heterostructure and temperature distribution have been considered.Annealing time has been optimized for pulse laser annealing.
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Project supported by the National Natural Science Foundation of China (No. 51072181)the Doctoral Fund of Ministry of Education of China (No. 20090101110044)
文摘ZnNiO thin films with different contents of Ni(0-10 at.%) were fabricated on quartz and Si(100) substrates by pulsed laser deposition(PLD).We measured the samples by X-ray diffraction(XRD),field-emission scanning electron microscope(FE-SEM),X-ray photoelectron spectroscopy(XPS),ultraviolet-visible spectrometer(UV-VIS),and Hall testing.When the Ni contents were below 3 at.%,partial Zn2+ ions were replaced by the Ni2+ ions without forming any other phases,which enhanced the conductivity of the film.When the Ni contents were above 3 at.%,Ni ions were at the interstitial sites,and Ni-related clusters and defects were able to emerge in the films,resulting in a worsening of electrical and optical properties.A ferromagnetic hysteresis with a coercive force of approximately 30 Oe was observed in the ZnNiO film with a Ni content of 3 at.% at room temperature.
基金Project(52378425)supported by the National Natural Science Foundation of ChinaProject(1053320221044)supported by the Fundamental Research Funds for the Central Universities,China。
文摘Irradiating hard rocks by a high-power laser can reduce localized hardness in the rocks;however,continuous lasers produce a large amount of melt that inhibits further heat absorption.Pulsed lasers allow rocks to absorb and dissipate energy and avoid melt formation.In this study,200 W nanosecond pulsed laser was used to irradiate granite.The effects of laser parameters on the thermal cracking morphology,temperature field,warming pattern,and Leeb hardness of the granite surface were analyzed.The optimal laser parameters for softening granite were determined by performing objective optimization in MATLAB using granite's melting point as the reference.Nanoindentation techniques were employed to assess the softening characteristics of the granite surface along the longitudinal direction.The results showed that three main forms of thermal damage occurred on the granite surface:oxidative decomposition,spalling,and melting.The damage state was affected by the average laser power,with the pulse width and repetition frequency affecting surface damage differently.Appropriate laser parameters effectively controlled the melt damage on the granite surface,and irradiation with nanosecond pulsed lasers effectively reduced surface hardness.However,excessive power can generate large amounts of hard melts and weaken the softening effect.
文摘BaFe_(12)O_(19)(BaM)thin films with thicknesses ranging from 15 nm–200 nm were deposited on Al_(2)O_(3)(0001)substrates by pulsed laser deposition(PLD).X-ray diffraction patterns show that a buffer layer with a thickness of nearly 60 nm forms on the substrate,and then a c-axis perpendicularly oriented Ba M thin film grows on the buffer layer.Atomic force microscopy results indicate that the Ba M thin film exhibits a spiral island growth mode on the buffer layer.Magnetic hysteresis loop results confirm that the buffer layer exhibits no significant magnetic anisotropy,while the Ba M thin film exhibits perpendicular magnetic anisotropy.The out-of-plane coercivity decreases with increasing Ba M thin-film thickness due to the combined effect of grain size growth and lattice strain relaxation.The 200 nm thick film exhibits optimum magnetic properties with M_(s)=319 emu/cm^(3) and H_(c)=1546 Oe.
基金funding from Grant No. HIDSS-0002 DASHH (Data Science in Hamburg-Helmholtz Graduate School for the Structure of Matter)partially supported by the Helmholtz Imaging platform through the project “Smart Phase.”
文摘Understanding the complex plasma dynamics in ultra-intense relativistic laser-solid interactions is of fundamental importance for applications of laser-plasma-based particle accelerators,the creation of high-energy-density matter,understanding planetary science,and laser-driven fusion energy.However,experimental efforts in this regime have been limited by the lack of accessibility of over-critical densities and the poor spatiotemporal resolution of conventional diagnostics.Over the last decade,the advent of femtosecond brilliant hard X-ray free-electron lasers(XFELs)has opened new horizons to overcome these limitations.Here,for the first time,we present full-scale spatiotemporal measurements of solid-density plasma dynamics,including preplasma generation with tens of nanometer scale length driven by the leading edge of a relativistic laser pulse,ultrafast heating and ionization at the main pulse arrival,the laser-driven blast wave,and transient surface return current-induced compression dynamics up to hundreds of picoseconds after interaction.These observations are enabled by utilizing a novel combination of advanced X-ray diagnostics including small-angle X-ray scattering,resonant X-ray emission spectroscopy,and propagation-based X-ray phase-contrast imaging simultaneously at the European XFEL-HED beamline station.
基金supported by the Youth Project of the National Natural Science Foundation of China(Grant No.22402024)the Postdoctoral Innovation Talents Support Program of China(Grant No.BX20230061)the Natural Science Foundation of Sichuan(Grant No.25QNJJ3094).P.M.-B.acknowledges funding from Deutsche Forschungsgemeinschaft(DFG,German Research Foundation)under Germany's Excellence Strategy-EXC 2089/1-390776260(e conversion).
文摘Pulsed laser deposition(PLD),as an advanced synthesis technology with unparalleled control over thin films,has evolved into a universal platform for optoelectronic materials engineering.Its unique advantages including precise stoichiometric transfer,heterogeneous structure preparation and in-situ monitoring enable the design of opto-electrocatalysts with controllable active sites.Traditional methods struggle to pinpoint active sites in hydrogen technologies such as fuel cells and water electrolysis,impeding catalyst customization and mechanistic understanding.Nevertheless,PLD remains underused here despite its outstanding performances in targeted photo-assisted electrocatalysts design.This review systematically explores the breakthrough achievements and provides detailed insights into photo-enhanced water electrolysis and fuel cells based on PLD.Beginning with the fundamentals of epitaxial film growth and film classification,particularly emphasis the related in situ optical analysis techniques.It subsequently highlights recent advances in electro-oxidation and reduction reactions of H_(2)and O_(2),demonstrating the control capabilities of PLD in precisely correlating the structure and activity at the atomic level.Finally,the review concludes by proposing scalable fabrication strategies and performance optimization frameworks to bridge fundamental insights with industrial-scale optoelectronic integration systems.
基金supported by the National Natural Science Foundation of China(Grant Nos.62071477 and 62101577)the Postgraduate Scientific Research Innovation Project of Hunan Province(Grant No.QL20230011).
文摘We demonstrate a high-peak-power master oscillator power amplifier burst-mode laser system that generates microsecond burst duration pulses at 355 nm with a GHz-adjustable intra-burst pulse frequency.In the fiber seed,a highbandwidth electro-optic modulator is employed to modulate a continuous-wave(CW)laser into a pulse train at GHz frequency.To acquire a microsecond rectangular burst pulse envelope,two acousto-optic modulators are used to chop the CW pulse train and generate a pre-compensation burst envelope.A three-stage neodymium-doped yttrium aluminum garnet amplifier boosts the burst-mode fiber seed’s burst energy of 1.65 J at 1064 nm.To achieve a high-power ultraviolet(UV)burst-mode laser,sum frequency generation in a LiB_(3)O_(5)crystal is employed to convert the wavelength,achieving over 300 kW of peak power at 1.15μs/10 Hz.The intra-burst pulse frequency of the UV burst laser can be adjustable from 1 to 10 GHz with a sinusoidal waveform.To the best of our knowledge,this paper represents the highest reported microsecond UV burst-mode laser in terms of output energy and peak power with the GHz-adjustable intra-burst frequency.The high-power microsecond UV burst-mode pulse laser can be directly used as a light-driven source in large-bandwidth/high-power microwave photonic systems,providing a long pulse width and high peak power laser while significantly improving the system’s multi-parameter adjustment capability and adaptability.
基金supported by the Natural Science Foundation of China(Nos.52022064 and 51971154).
文摘The development of highly active and cost-effective catalysts for the full pH range of the hydrogen evolution reaction(HER)to meet the industrial application demands is an urgent challenge.In this work,the performance and structure–activityrelationships of CuIr alloys prepared by the pulsed laser ablation in liquid technique as full pH range HER catalysts wereinvestigated.Results indicated that Ir is doped into the Cu matrix as single atoms in CuIr-0.1,and CuIr-0.1 single-atom alloys(SAAs)exhibit superior HER performance and stability across the full pH range,with overpotentials of 135,203,and 172 mVat the current density of 10 mA/cm^(2)in acidic,neutral,and alkaline electrolytes,respectively.The enhanced performance ofCuIr-0.1 SAAs can be attributed to the abundant active sites and accelerated reaction kinetics brought about by the electroniceffects.This work successfully alloyed two immiscible metals to improve the catalytic performance,providing an avenue forthe development of highly efficient and versatile HER catalysts for industrial applications.
基金Project supported by the National Key R&D Program of China(Grant No.2022YFA1402404)the National Natural Science Foundation of China(Grant Nos.T2394473,624B2070,and 62274085)。
文摘Type-II Dirac semimetal PtTe2is a promising candidate for various electronic device applications due to its high carrier mobility,high conductivity,and air stability.In this work,we report on the growth of large-scale PtTe_(2)films by the pulsed laser deposition(PLD)and the comparison of the magnetotransport properties with the PtTe2films grown by the chemical vapor deposition(CVD).The low-temperature Hall curves of the PLD-grown films exhibit a linear behavior,in contrast with the nonlinear characteristic of the Hall behavior observed in CVD-grown films,in which a defect gradient is introduced.Meanwhile,both PtTe2films show weak antilocalization at low temperatures,which is attributed to the strong spin–orbit coupling.
基金Supported by Guangdong Major Project of Basic and Applied Research,China(Grant No.2019B030302010)National Natural Science Foundation of China (Grant Nos.51735003,52205456)
文摘Avoiding crystallization while maintaining the original microstructure and mechanical properties of the material are long-term goals of laser welding of Zr-based bulk metallic glass(BMG).In this paper,the effect of pulsed laser welding parameters on the microstructure,crystallization degree,and mechanical properties of Zr57Nb5Cu15.4Ni12.6Al10 BMG is investigated.Non-crystallized welding forming of a zirconium-based amorphous alloy is achieved by optimizing the process parameters of pulsed laser welding.The crystallization degree of Zr-based BMG is mainly determined by the welding speed and power.The welding depth and crystallization area fraction increase with an increase in the effective peak power density.The optimized welding process can effectively reduce the heat accumulation of the weld,thus avoiding crystallization.The flexural strength of the weld can be maintained at 96.5%of the matrix.
基金supported by BMBF-Project No.05P24PF1DFG Project No.PU 213/6-3.
文摘We propose an all-optical,single-laser-pulse scheme for generating a dense relativistic strongly magnetized electron-positron pair plasma.The scheme involves the interaction of an extremely intense(I■10^(24) W/cm^(2))circularly polarized laser pulse with a solid-density target containing a conical cavity.Through full-scale three-dimensional particle-in-cell simulations that account for quantum electrodynamic effects,it is shown that this interaction results in two significant outcomes:first,the generation of quasi-static magnetic fields reaching tens of gigagauss,and,second,the production of large quantities of electron-positron pairs(up to 10^(13))via the Breit-Wheeler process.The e^(-)e^(+)plasma becomes trapped in the magnetic field and remains confined in a small volume for hundreds of femtoseconds,far exceeding the laser timescale.The dependence of pair plasma parameters,as well as the efficiency of plasma production and confinement,is discussed in relation to the properties of the laser pulse and the target.Realizing this scheme experimentally would enable the investigation of physical processes relevant to extreme astrophysical environments.
基金supported by the National Natural Science Foundation of China(Grant No.12374238)the Postdoctoral Science Foundation of Shaanxi Province (Grant No.2024BSHSDZZ148)Ministry of Science and Higher Education of Russian Federation (Grant No.FSRZ 2023-0006)。
文摘A singlet diatomic molecule naturally carries doubly degenerate ±Λ states when the projection of the total electronic angular momentum onto the internuclear axis is nonzero. These doubly degenerate states contribute equally in conventional measurements and are thus treated the same in corresponding simulations. In this study, we demonstrate that in resonant excitation by intense laser pulses, the doubly degenerate ±Λ states must be clearly identified. This is exemplified in the X^(1)Σ → A^(1)Π transition of CO molecules. This distinction becomes especially important in the case of circularly polarized radiation. We attribute this phenomenon to the interference of electron-rotational pathways in the strong-field coupled transition with the ±Λ-state of the excited Π state. This research sheds light on the fundamental aspects of intense laser-molecule interactions when extending conventional theories.
基金supported by the National Natural Science Foundation of China(Grant Nos.12375236 and 12135009)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant Nos.XDA25050100 and XDA25010100).
文摘The generation and reconnection of magneticflux ropes in a plasma irradiated by two Laguerre–Gaussian laser pulses with different frequen-cies and opposite topological charges are investigated numerically by particle-in-cell simulations.It is shown that twisted plasma currents and hence magneticflux ropes can be effectively generated as long as the laser frequency difference matches the electron plasma frequency.More importantly,subsequent reconnection of magneticflux ropes can occur.Typical signatures of magnetic reconnection,such as magnetic island formation and plasma heating,are identified in the reconnection of magneticflux ropes.Notably,it is found that a strong axial magneticfield can be generated on the axis,owing to the azimuthal current induced during the reconnection of the ropes.This indicates that in the reconnection of magneticflux ropes,the energy can be transferred not only from the magneticfield to the plasma but also from the plasma current back to the magneticfield.This work opens a new avenue to the study of magneticflux ropes,which helps in understanding magnetic topology changes,and resultant magnetic energy dissipation,plasma heating,and particle acceleration found in solarflares,and magnetic confinement fusion devices.
