Stretchable electronic sensing devices are defining the path toward wearable electronics. High-performance flexible strain sensors attached on clothing or human skin are required for potential applications in the ente...Stretchable electronic sensing devices are defining the path toward wearable electronics. High-performance flexible strain sensors attached on clothing or human skin are required for potential applications in the entertainment,health monitoring, and medical care sectors. In this work,conducting copper electrodes were fabricated onpolydimethylsiloxane as sensitive stretchable microsensors by integrating laser direct writing and transfer printing approaches. The copper electrode was reduced from copper salt using laser writing rather than the general approach of printing with pre-synthesized copper or copper oxide nanoparticles. An electrical resistivity of 96 l X cm was achieved on 40-lm-thick Cu electrodes on flexible substrates. The motion sensing functionality successfully demonstrated a high sensitivity and mechanical robustness.This in situ fabrication method leads to a path toward electronic devices on flexible substrates.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
Currently,laser-induced structural modifications in optical materials have been an active field of research.In this paper,we reported structural modifications in the bulk of sapphire due to picosecond(ps)laser filamen...Currently,laser-induced structural modifications in optical materials have been an active field of research.In this paper,we reported structural modifications in the bulk of sapphire due to picosecond(ps)laser filamentation and analyzed the ionization dynamics of the filamentation.Numerical simulations uncovered that the high-intensity ps laser pulses generate plasma through multi-photon and avalanche ionizations that leads to the creation of two distinct types of structural changes in the material.The experimental bulk modifications consist of a void like structures surrounded by cracks which are followed by a submicrometer filamentary track.By increasing laser energy,the length of the damage and filamentary track appeared to increase.In addition,the transverse diameter of the damage zone increased due to the electron plasma produced by avalanche ionizations,but no increase in the filamentary zone diameter was observed with increasing laser energy.展开更多
Laser beam welding of aluminum alloys is expected to offer good mechanical properties of welded joints. In this experimental work reported, CO2 laser beam autogenoas welding and wire feed welding are conducted on 4 mm...Laser beam welding of aluminum alloys is expected to offer good mechanical properties of welded joints. In this experimental work reported, CO2 laser beam autogenoas welding and wire feed welding are conducted on 4 mm thick 5083- H321 aluminum alloy sheets at different welding variables. The mechanical properties and microstructure characteristics of the welds are evaluated through tensile tests, micro-hardness tests, optical microscopy and scanning electron microscopy （SEM）. Experimental results indicate that both the tensile strength and hardness of laser beam welds are affected by the constitution of filler material, except the yield strength. The soften region of laser beam welds is not in the heat-affected zone （ HAZ ）. The tensile fracture of laser beam welded specimens takes place in the weld zone and close to the weld boundary because of different filler materials. Some pores are found on the fracture face, including hydrogen porosities and blow holes, but these pores have no influence on the tensile strength of laser beam welds. Tensile strength values of laser beam welds with filler wire are up to 345.57 MPa, 93% of base material values, and yield strengths of laser beam welds are equivalent to those of base metal （264. 50 MPa）.展开更多
Optimum laser configurations are presented to achieve high illumination uniformity with directly driven inertial confinement fusion targets.Assuming axisymmetric absorption pattern of individual laser beams,theoretica...Optimum laser configurations are presented to achieve high illumination uniformity with directly driven inertial confinement fusion targets.Assuming axisymmetric absorption pattern of individual laser beams,theoretical models are reviewed in terms of the number of laser beams,system imperfection,and laser beam patterns.Utilizing a self-organizing system of charged particles on a sphere,a simple numerical model is provided to give an optimal configuration for an arbitrary number of laser beams.As a result,such new configurations as“M48”and“M60”are found to show substantially higher illumination uniformity than any other existing direct drive systems.A new polar direct-drive scheme is proposed with the laser axes keeping off the target center,which can be applied to laser configurations designed for indirectly driven inertial fusion.展开更多
The influence of the picosecond(ps) pulsed burst with a nanosecond scale of temporal separation(50 ns) on filamentary traces in sapphire substrate is investigated. The spatiotemporal evolution of the filamentary plasm...The influence of the picosecond(ps) pulsed burst with a nanosecond scale of temporal separation(50 ns) on filamentary traces in sapphire substrate is investigated. The spatiotemporal evolution of the filamentary plasma string induced by sub-pulses of the burst-mode is revealed according to the analysis of the instantaneous photoluminescence images. Due to the presence of residual plasma, the energy loss of sub-pulse during the balancing of self-focusing effect is reduced, and thus refreshes the plasma via refocusing. The refreshed plasma peak generated by the subsequent subpulse appears at relatively low density positions in the formed filamentary plasma string, which results in more uniform densities and less spatial overlap among the plasma peaks. The continuity and uniformity of the filamentary trace in sapphire are enhanced by the burst-mode. Besides, the burst filamentary propagation can also remain effective when the sub-pulse energy is below the self-focusing threshold. Based on this uniform and precise energy propagation mode, the feasibility of its use for the laser lift-off(LLO) process is verified.展开更多
In our previous study, metals have been used as absorbers in the clear plastic laser transmission welding. The effects of metal thermal conductivity on the welding quality are investigated in the present work. Four me...In our previous study, metals have been used as absorbers in the clear plastic laser transmission welding. The effects of metal thermal conductivity on the welding quality are investigated in the present work. Four metals with distinctly different thermal conductivities, i.e., titanium, nickel, molybdenum, and copper, are selected as light absorbers. The lap welding is conducted with an 808 nm diode laser and simulation experiments are also conducted. Nickel electroplating test is carried out to minimize the side-effects from different light absorptivities of different metals. The results show that the welding with an absorber of higher thermal conductivity can accommodate higher laser input power before smoking, which produces a wider and stronger welding seam.The positive role of the higher thermal conductivity can be attributed to the fact that a desirable thermal field distribution for the molecular diffusion and entanglement is produced from the case with a high thermal conductivity.展开更多
Laser fusion brazing welding was proposed.Galvanized steel/AA6061 lapped joint was obtained by laser fusion brazing welding technique using the laser-induced aluminium molten pool spreading and wetting the solid steel...Laser fusion brazing welding was proposed.Galvanized steel/AA6061 lapped joint was obtained by laser fusion brazing welding technique using the laser-induced aluminium molten pool spreading and wetting the solid steel surface.Wide joint interface was formed using the rectangular laser beam coupled with the synchronous powder feeding.The result showed that the tiny structure with the composition of a-Al and Al–Si eutectic was formed in the weld close to the Al side.And close to the steel side,a layer of compact Fe–Al–Si intermetallics,including the Al-rich FeAl3,Fe2Al5 phases and Al–Fe–Si s1 phase,was generated with the thickness of about 10–20 lm.Transverse tensile shows the brittlefractured characteristic along to the seam/steel interface with the maximum yield strength of 152.5 MPa due to the existence of hardening phases s1 and Al–Fe intermetallics.展开更多
The microstructures and corrosion behaviors of AA2198-T851 alloy and weld were analyzed under corrosive conditions. Weld was formed using an innovative fiber laser welding process with AA2319 Al-Cu filler wire. The me...The microstructures and corrosion behaviors of AA2198-T851 alloy and weld were analyzed under corrosive conditions. Weld was formed using an innovative fiber laser welding process with AA2319 Al-Cu filler wire. The metallurgic morphology and distribution of the chemical compositions were determined using imaging techniques such as optical micrograph, scanning electron micrograph, high-resolution transmission electron microscopy, energy-dispersive X-ray spectrometry and X-ray diffraction. Corrosion was evaluated using an immersion test and electrochemical impedance spectroscopy in 3.5% NaC1 solution at room temperature. Results indicate that the parent alloy suffered from pitting corrosion during the initial 4-h immersion which was caused by the inhomogeneous distribution of its chemical compo- nents and the different intermetallics formed during the rolling process. The weld experienced dendritic boundary corrosion under the same conditions due to the addition of the Al-Cu filler and rapid solidification during laser welding, which led to the precipitates Cu enrichment along the grain boundary. When a welding joint was immersed in the solution for 5 days, a big crack was observed across the center of the weld. In comparison, there was good corrosion resistance in the heat- affected zone with a compact protective film.展开更多
The interaction of micro-bubbles with ultra-intense laser pulses has been shown to generate ultra-high proton densities and correspondingly high electric fields.Weinvestigate the possibility of using such a combinatio...The interaction of micro-bubbles with ultra-intense laser pulses has been shown to generate ultra-high proton densities and correspondingly high electric fields.Weinvestigate the possibility of using such a combination to study the fundamental physical phenomenon of vacuum polarization.With current or near-future laser systems,measurement of vacuum polarization via the bending of gamma rays that pass near imploded microbubbles may be possible.Since it is independent of photon energy to within the leading-order solution of the Heisenberg–Euler Lagrangian and the geometric optics approximation,the corresponding index of refraction can dominate the indices of refraction due to other effects at sufficiently high photon energies.We consider the possibility of its application to a transient gamma-ray lens.展开更多
Targets for low-adiabat direct-drive-implosion experiments on OMEGA must meet rigorous specifications and tight tolerances on the diameter,wall thickness,wall-thickness uniformity,and presence of surface features.Of t...Targets for low-adiabat direct-drive-implosion experiments on OMEGA must meet rigorous specifications and tight tolerances on the diameter,wall thickness,wall-thickness uniformity,and presence of surface features.Of these,restrictions on the size and number of defects(bumps and depressions)on the surface are the most challenging.The properties of targets that are made using vapor-deposition and solution-based microencapsulation techniques are reviewed.Targets were characterized using confocal microscopy,bright-and dark-field microscopy,atomic force microscopy,electron microscopy,and interferometry.Each technique has merits and limitations,and a combination of these techniques is necessary to adequately characterize a target.The main limitation with the glow-discharge polymerization(GDP)method for making targets is that it produces hundreds of domes with a lateral dimension of 0.7-2 μm.Polishing these targets reduces the size of some but not all domes,but it adds scratches and grooves to the surface.Solution-made polystyrene shells lack the dome features of GDP targets but have hundreds of submicrometer-size voids throughout the wall of the target;a few of these voids can be as large as~12 μm at the surface.展开更多
X-ray absorption spectroscopy is a well-accepted diagnostic for experimental studies of warm dense matter.It requires a short-lived X-ray source of sufficiently high emissivity and without characteristic lines in the ...X-ray absorption spectroscopy is a well-accepted diagnostic for experimental studies of warm dense matter.It requires a short-lived X-ray source of sufficiently high emissivity and without characteristic lines in the spectral range of interest.In the present work,we discuss how to choose an optimum material and thickness to get a bright source in the wavelength range 2A–6A(∼2 keV to 6 keV)by considering relatively low-Z elements.We demonstrate that the highest emissivity of solid aluminum and silicon foil targets irradiated with a 1-ps high-contrast sub-kJ laser pulse is achieved when the target thickness is close to 10μm.An outer plastic layer can increase the emissivity even further.展开更多
By using a photonic crystal fiber, a supercontinuum source with output power up to 1.7W, pumped by a passively mode-locked diode-pumped Nd：YVO4 picosecond laser is obtained. A spectral width of the supercontinuum is ...By using a photonic crystal fiber, a supercontinuum source with output power up to 1.7W, pumped by a passively mode-locked diode-pumped Nd：YVO4 picosecond laser is obtained. A spectral width of the supercontinuum is 1700 nm （500–2200 nm） with the 5 dB spectral width approximately 1000 nm （1200–2200 nm）. This high power wide band supercontinuum source meets the demand of many applications such as optical coherence tomography, frequency metrology and wavelength-division-multiplexing systems. The evolution of the supercontinuum with the increasing pump power is presented and analyzed.展开更多
The Zeeman splitting effect is observed in a strong magnetic field generated by a laser-driven coil.The expanding plasma from the coil wire surface is concentrated at the coil center and interacts with the simultaneou...The Zeeman splitting effect is observed in a strong magnetic field generated by a laser-driven coil.The expanding plasma from the coil wire surface is concentrated at the coil center and interacts with the simultaneously generated magnetic field.The Cu I spectral lines at wavelengths of 510.5541,515.3235,and 521.8202 nm are detected and analyzed.The splittings of spectral lines are used to estimate the magnetic field strength at the coil center as∼31.4±15.7 T at a laser intensity of∼5.6310^(15) W/cm^(2),which agrees well with measurements using a B-dot probe.Some other plasma parameters of the central plasma disk are also studied.The temperature is evaluated from the Cu I spectral line intensity ratio,while the electron density is estimated from the Stark broadening effect.展开更多
Brillouin light scattering technique can be successfully used to determine the whole set of elastic and piezoelectric constants of a ZnO single crystal irradiated by different laser energy densities, into a micron ran...Brillouin light scattering technique can be successfully used to determine the whole set of elastic and piezoelectric constants of a ZnO single crystal irradiated by different laser energy densities, into a micron range （radiation layer thickness）. It is found that the scattering intensity, the linewidth and the Brillouin scattering shift of acoustic phonons are all strongly dependent on laser energy density. Based on the sound propagation equations and these results, the directional dependences of the compressional and shear moduli of the irradiated ZnO sample in the （001） plane are investigated. It is found that under an appropriate laser condition, 248 nm KrF excimer laser irradiation can significantly improve the surface quality and increase the elastic properties of ZnO single crystal. This procedure has potential applications in the fabrication of ZnO-based surface acoustic wave and optic-electronic devices.展开更多
Based on the dispersion relation of intense laser pulse propagating in gradually ionized plasma, this paper discusses the frequency modulation induced by ionization of an ultra-short intense laser pulse interacting wi...Based on the dispersion relation of intense laser pulse propagating in gradually ionized plasma, this paper discusses the frequency modulation induced by ionization of an ultra-short intense laser pulse interacting with a gas target. The relationship between the frequency modulation and the ionization rate, the plasmas frequency variation, and the polarization of atoms （ions） is analysed. The numerical results indicate that, at high frequency, the polarization of atoms （ions） plays a more important role than plasma frequency variation in modulating the laser frequency, and the laser frequency variation is different at different positions of the laser pulse.展开更多
Previous studies have shown some correlations between the optical properties of objects and their surface patterns. We fabricate tens of micrometer period gratings by femtosecond laser direct writing technology on pol...Previous studies have shown some correlations between the optical properties of objects and their surface patterns. We fabricate tens of micrometer period gratings by femtosecond laser direct writing technology on polished nickel targets and measure their thermal radiation spectra at a temperature of 623 K by Fourier transform infrared （FTIR） spectrometry. The results show an obvious major enhanced peak in which the wavelength is slightly larger than the grating period. Surface plasmon resonance （SPR） and Kircbhoff＇s law of thermal radiation are applied to give this phenomenon a preliminary explanation. In addition, we utilized rigorous coupled wave analysis （RCWA） to simulate the absorption spectrum of the grating surface. The experiment results show good agreement with the simulation results.展开更多
The nonlinear optic characteristics of an intense laser pulse propagating in partially stripped plasmas are investigated analytically. The phase and group velocity of the laser pulse propagation as well as the three g...The nonlinear optic characteristics of an intense laser pulse propagating in partially stripped plasmas are investigated analytically. The phase and group velocity of the laser pulse propagation as well as the three general expressions governing the nonlinear optic behavior, based on the photon number conservation, are obtained by considering the partially stripped plasma as a nonlinear optic medium. The numerical result shows that the presence of the bound electrons in partially stripped plasma can significantly change the propagating property of the intense laser pulse.展开更多
In this paper, we investigate the laser irradiation of ZnO single crystals and its influence on photoluminescence. Our study shows that the photoluminescence of ZnO single crystals strongly depends on surface morpholo...In this paper, we investigate the laser irradiation of ZnO single crystals and its influence on photoluminescence. Our study shows that the photoluminescence of ZnO single crystals strongly depends on surface morphologies. The ultraviolet emissions of laser treated-ZnO under 200 mJ/cm^2 become stronger, whereas for those deteriorated by irradiation above 200 mJ/cm^2, the green emissions centred at 2.53 eV are significantly enhanced with a red-shift to 2.19 eV, probably due to the changes in the charge states of the defects. Enhanced yellow-green emissions are well resolved into four peaks at around 1.98, 2.19, 2.36, and 2.53 eV due to a shallow irradiation depth. Possible origins are proposed and discussed.展开更多
Reviewed are the present status and future prospects of the laser fusionresearch at the ILE Osaka. The Gekko XII and Peta Watt laser system have been operated forinvestigating the implosion hydrodynamics, fast ignitio...Reviewed are the present status and future prospects of the laser fusionresearch at the ILE Osaka. The Gekko XII and Peta Watt laser system have been operated forinvestigating the implosion hydrodynamics, fast ignition, and the relativistic laser plasmainteractions and so on. In particular, the fast ignition experiments with cone shell target havebeen in progress as the UK and US-Japan collaboration programs. In the experiments, the implodedhigh density plasmas are heated by irradiating 500 J level peta-watt laser pulse. The thermalneutron yield is found to increase by three orders of magnitude by injecting the peta-watt laserinto the cone shell target. The Rayleigh-Taylor instability experiment results are also reviewed isthis paper.展开更多
基金supported by National Natural Science Foundation of China (51575016)the Beijing Oversea High-Level Talent Project+1 种基金strategic research Grant (KZ20141000500, B-type) of Beijing Natural Science Foundation P.R. Chinathe support by the China Scholarship Council (20160654015) for his research stay at the Institute of Physical and Chemical Research,Wako, Japan
文摘Stretchable electronic sensing devices are defining the path toward wearable electronics. High-performance flexible strain sensors attached on clothing or human skin are required for potential applications in the entertainment,health monitoring, and medical care sectors. In this work,conducting copper electrodes were fabricated onpolydimethylsiloxane as sensitive stretchable microsensors by integrating laser direct writing and transfer printing approaches. The copper electrode was reduced from copper salt using laser writing rather than the general approach of printing with pre-synthesized copper or copper oxide nanoparticles. An electrical resistivity of 96 l X cm was achieved on 40-lm-thick Cu electrodes on flexible substrates. The motion sensing functionality successfully demonstrated a high sensitivity and mechanical robustness.This in situ fabrication method leads to a path toward electronic devices on flexible substrates.
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National Natural Science Foundation of China(51575013,51275011)National Key R&D Program of China(2018 YFB1107500)
文摘Currently,laser-induced structural modifications in optical materials have been an active field of research.In this paper,we reported structural modifications in the bulk of sapphire due to picosecond(ps)laser filamentation and analyzed the ionization dynamics of the filamentation.Numerical simulations uncovered that the high-intensity ps laser pulses generate plasma through multi-photon and avalanche ionizations that leads to the creation of two distinct types of structural changes in the material.The experimental bulk modifications consist of a void like structures surrounded by cracks which are followed by a submicrometer filamentary track.By increasing laser energy,the length of the damage and filamentary track appeared to increase.In addition,the transverse diameter of the damage zone increased due to the electron plasma produced by avalanche ionizations,but no increase in the filamentary zone diameter was observed with increasing laser energy.
基金This research was supported by Major Subject Foundation of Beijing University of Technology
文摘Laser beam welding of aluminum alloys is expected to offer good mechanical properties of welded joints. In this experimental work reported, CO2 laser beam autogenoas welding and wire feed welding are conducted on 4 mm thick 5083- H321 aluminum alloy sheets at different welding variables. The mechanical properties and microstructure characteristics of the welds are evaluated through tensile tests, micro-hardness tests, optical microscopy and scanning electron microscopy （SEM）. Experimental results indicate that both the tensile strength and hardness of laser beam welds are affected by the constitution of filler material, except the yield strength. The soften region of laser beam welds is not in the heat-affected zone （ HAZ ）. The tensile fracture of laser beam welded specimens takes place in the weld zone and close to the weld boundary because of different filler materials. Some pores are found on the fracture face, including hydrogen porosities and blow holes, but these pores have no influence on the tensile strength of laser beam welds. Tensile strength values of laser beam welds with filler wire are up to 345.57 MPa, 93% of base material values, and yield strengths of laser beam welds are equivalent to those of base metal （264. 50 MPa）.
基金This work was supported by the Japan Society for the Promotion of Science(JSPS).
文摘Optimum laser configurations are presented to achieve high illumination uniformity with directly driven inertial confinement fusion targets.Assuming axisymmetric absorption pattern of individual laser beams,theoretical models are reviewed in terms of the number of laser beams,system imperfection,and laser beam patterns.Utilizing a self-organizing system of charged particles on a sphere,a simple numerical model is provided to give an optimal configuration for an arbitrary number of laser beams.As a result,such new configurations as“M48”and“M60”are found to show substantially higher illumination uniformity than any other existing direct drive systems.A new polar direct-drive scheme is proposed with the laser axes keeping off the target center,which can be applied to laser configurations designed for indirectly driven inertial fusion.
基金Project(51975017) supported by the National Natural Science Foundation of ChinaProject(KZ202110005012) supported by the Scientific Research Project of Beijing Educational Committee+1 种基金ChinaProject(2018YFB1107500) supported by the National Key R&D Program of China。
文摘The influence of the picosecond(ps) pulsed burst with a nanosecond scale of temporal separation(50 ns) on filamentary traces in sapphire substrate is investigated. The spatiotemporal evolution of the filamentary plasma string induced by sub-pulses of the burst-mode is revealed according to the analysis of the instantaneous photoluminescence images. Due to the presence of residual plasma, the energy loss of sub-pulse during the balancing of self-focusing effect is reduced, and thus refreshes the plasma via refocusing. The refreshed plasma peak generated by the subsequent subpulse appears at relatively low density positions in the formed filamentary plasma string, which results in more uniform densities and less spatial overlap among the plasma peaks. The continuity and uniformity of the filamentary trace in sapphire are enhanced by the burst-mode. Besides, the burst filamentary propagation can also remain effective when the sub-pulse energy is below the self-focusing threshold. Based on this uniform and precise energy propagation mode, the feasibility of its use for the laser lift-off(LLO) process is verified.
基金Supported by the National Key R&D Program of China under Grant No 2016YFA0401100the National Natural Science Foundation of China under Grant No 61575129the National High-Technology Research and Development Program of China under Grant No 2015AA021102
文摘In our previous study, metals have been used as absorbers in the clear plastic laser transmission welding. The effects of metal thermal conductivity on the welding quality are investigated in the present work. Four metals with distinctly different thermal conductivities, i.e., titanium, nickel, molybdenum, and copper, are selected as light absorbers. The lap welding is conducted with an 808 nm diode laser and simulation experiments are also conducted. Nickel electroplating test is carried out to minimize the side-effects from different light absorptivities of different metals. The results show that the welding with an absorber of higher thermal conductivity can accommodate higher laser input power before smoking, which produces a wider and stronger welding seam.The positive role of the higher thermal conductivity can be attributed to the fact that a desirable thermal field distribution for the molecular diffusion and entanglement is produced from the case with a high thermal conductivity.
基金financially supported by the National Natural Science Foundation of China (No.50875005)Beijing Natural Science Foundation (No.3102005)
文摘Laser fusion brazing welding was proposed.Galvanized steel/AA6061 lapped joint was obtained by laser fusion brazing welding technique using the laser-induced aluminium molten pool spreading and wetting the solid steel surface.Wide joint interface was formed using the rectangular laser beam coupled with the synchronous powder feeding.The result showed that the tiny structure with the composition of a-Al and Al–Si eutectic was formed in the weld close to the Al side.And close to the steel side,a layer of compact Fe–Al–Si intermetallics,including the Al-rich FeAl3,Fe2Al5 phases and Al–Fe–Si s1 phase,was generated with the thickness of about 10–20 lm.Transverse tensile shows the brittlefractured characteristic along to the seam/steel interface with the maximum yield strength of 152.5 MPa due to the existence of hardening phases s1 and Al–Fe intermetallics.
基金financially supported by the National Natural Science Foundation of China (Grant Number: 51505010)Beijing Natural Science Foundation (Grant Number: 2152007)
文摘The microstructures and corrosion behaviors of AA2198-T851 alloy and weld were analyzed under corrosive conditions. Weld was formed using an innovative fiber laser welding process with AA2319 Al-Cu filler wire. The metallurgic morphology and distribution of the chemical compositions were determined using imaging techniques such as optical micrograph, scanning electron micrograph, high-resolution transmission electron microscopy, energy-dispersive X-ray spectrometry and X-ray diffraction. Corrosion was evaluated using an immersion test and electrochemical impedance spectroscopy in 3.5% NaC1 solution at room temperature. Results indicate that the parent alloy suffered from pitting corrosion during the initial 4-h immersion which was caused by the inhomogeneous distribution of its chemical compo- nents and the different intermetallics formed during the rolling process. The weld experienced dendritic boundary corrosion under the same conditions due to the addition of the Al-Cu filler and rapid solidification during laser welding, which led to the precipitates Cu enrichment along the grain boundary. When a welding joint was immersed in the solution for 5 days, a big crack was observed across the center of the weld. In comparison, there was good corrosion resistance in the heat- affected zone with a compact protective film.
文摘The interaction of micro-bubbles with ultra-intense laser pulses has been shown to generate ultra-high proton densities and correspondingly high electric fields.Weinvestigate the possibility of using such a combination to study the fundamental physical phenomenon of vacuum polarization.With current or near-future laser systems,measurement of vacuum polarization via the bending of gamma rays that pass near imploded microbubbles may be possible.Since it is independent of photon energy to within the leading-order solution of the Heisenberg–Euler Lagrangian and the geometric optics approximation,the corresponding index of refraction can dominate the indices of refraction due to other effects at sufficiently high photon energies.We consider the possibility of its application to a transient gamma-ray lens.
基金This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944the University of Rochester,and the New York State Energy Research and Development Authority.
文摘Targets for low-adiabat direct-drive-implosion experiments on OMEGA must meet rigorous specifications and tight tolerances on the diameter,wall thickness,wall-thickness uniformity,and presence of surface features.Of these,restrictions on the size and number of defects(bumps and depressions)on the surface are the most challenging.The properties of targets that are made using vapor-deposition and solution-based microencapsulation techniques are reviewed.Targets were characterized using confocal microscopy,bright-and dark-field microscopy,atomic force microscopy,electron microscopy,and interferometry.Each technique has merits and limitations,and a combination of these techniques is necessary to adequately characterize a target.The main limitation with the glow-discharge polymerization(GDP)method for making targets is that it produces hundreds of domes with a lateral dimension of 0.7-2 μm.Polishing these targets reduces the size of some but not all domes,but it adds scratches and grooves to the surface.Solution-made polystyrene shells lack the dome features of GDP targets but have hundreds of submicrometer-size voids throughout the wall of the target;a few of these voids can be as large as~12 μm at the surface.
基金The study was supported financially by the Russian Foundation for Basic Research(Grant No.20-02-00790)the Joint Institute for High Temperatures of the Russian Academy of Sciences(Topic Grant No.01201357846)The UK team received financial support from the Engineering and Physical Sciences Research Council(Grant Nos.EP/L01663X/1 and EP/H012605/1).
文摘X-ray absorption spectroscopy is a well-accepted diagnostic for experimental studies of warm dense matter.It requires a short-lived X-ray source of sufficiently high emissivity and without characteristic lines in the spectral range of interest.In the present work,we discuss how to choose an optimum material and thickness to get a bright source in the wavelength range 2A–6A(∼2 keV to 6 keV)by considering relatively low-Z elements.We demonstrate that the highest emissivity of solid aluminum and silicon foil targets irradiated with a 1-ps high-contrast sub-kJ laser pulse is achieved when the target thickness is close to 10μm.An outer plastic layer can increase the emissivity even further.
文摘By using a photonic crystal fiber, a supercontinuum source with output power up to 1.7W, pumped by a passively mode-locked diode-pumped Nd：YVO4 picosecond laser is obtained. A spectral width of the supercontinuum is 1700 nm （500–2200 nm） with the 5 dB spectral width approximately 1000 nm （1200–2200 nm）. This high power wide band supercontinuum source meets the demand of many applications such as optical coherence tomography, frequency metrology and wavelength-division-multiplexing systems. The evolution of the supercontinuum with the increasing pump power is presented and analyzed.
基金This work was supported in part by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant Nos.XDA25010100,XDA25010300,and XDA25030100)the National Natural Science Foundation of China(Grant Nos.U1930107 and 11827807)the Japanese Ministry of Education,Science,Sports,and Culture through Grants-in-Aid,KAKENHI(Grant No.21H04454).
文摘The Zeeman splitting effect is observed in a strong magnetic field generated by a laser-driven coil.The expanding plasma from the coil wire surface is concentrated at the coil center and interacts with the simultaneously generated magnetic field.The Cu I spectral lines at wavelengths of 510.5541,515.3235,and 521.8202 nm are detected and analyzed.The splittings of spectral lines are used to estimate the magnetic field strength at the coil center as∼31.4±15.7 T at a laser intensity of∼5.6310^(15) W/cm^(2),which agrees well with measurements using a B-dot probe.Some other plasma parameters of the central plasma disk are also studied.The temperature is evaluated from the Cu I spectral line intensity ratio,while the electron density is estimated from the Stark broadening effect.
基金Project supported by the National Natural Science Foundation of China (Grant No. 10974009)
文摘Brillouin light scattering technique can be successfully used to determine the whole set of elastic and piezoelectric constants of a ZnO single crystal irradiated by different laser energy densities, into a micron range （radiation layer thickness）. It is found that the scattering intensity, the linewidth and the Brillouin scattering shift of acoustic phonons are all strongly dependent on laser energy density. Based on the sound propagation equations and these results, the directional dependences of the compressional and shear moduli of the irradiated ZnO sample in the （001） plane are investigated. It is found that under an appropriate laser condition, 248 nm KrF excimer laser irradiation can significantly improve the surface quality and increase the elastic properties of ZnO single crystal. This procedure has potential applications in the fabrication of ZnO-based surface acoustic wave and optic-electronic devices.
基金Project supported by the National Science Foundation of China （Grant Nos 10574010 and 10276002） and by Specialized Research Fund for the Doctoral Program of Higher Education （SRFDP） of China （Grant No 20050005016）
文摘Based on the dispersion relation of intense laser pulse propagating in gradually ionized plasma, this paper discusses the frequency modulation induced by ionization of an ultra-short intense laser pulse interacting with a gas target. The relationship between the frequency modulation and the ionization rate, the plasmas frequency variation, and the polarization of atoms （ions） is analysed. The numerical results indicate that, at high frequency, the polarization of atoms （ions） plays a more important role than plasma frequency variation in modulating the laser frequency, and the laser frequency variation is different at different positions of the laser pulse.
基金supported by the National Natural Science Foundation of China(Grant No.51275012)
文摘Previous studies have shown some correlations between the optical properties of objects and their surface patterns. We fabricate tens of micrometer period gratings by femtosecond laser direct writing technology on polished nickel targets and measure their thermal radiation spectra at a temperature of 623 K by Fourier transform infrared （FTIR） spectrometry. The results show an obvious major enhanced peak in which the wavelength is slightly larger than the grating period. Surface plasmon resonance （SPR） and Kircbhoff＇s law of thermal radiation are applied to give this phenomenon a preliminary explanation. In addition, we utilized rigorous coupled wave analysis （RCWA） to simulate the absorption spectrum of the grating surface. The experiment results show good agreement with the simulation results.
基金the National Natural Science Foundation of China under
文摘The nonlinear optic characteristics of an intense laser pulse propagating in partially stripped plasmas are investigated analytically. The phase and group velocity of the laser pulse propagation as well as the three general expressions governing the nonlinear optic behavior, based on the photon number conservation, are obtained by considering the partially stripped plasma as a nonlinear optic medium. The numerical result shows that the presence of the bound electrons in partially stripped plasma can significantly change the propagating property of the intense laser pulse.
基金Project supported by the National Natural Science Foundation of China(Grant No.10974009)
文摘In this paper, we investigate the laser irradiation of ZnO single crystals and its influence on photoluminescence. Our study shows that the photoluminescence of ZnO single crystals strongly depends on surface morphologies. The ultraviolet emissions of laser treated-ZnO under 200 mJ/cm^2 become stronger, whereas for those deteriorated by irradiation above 200 mJ/cm^2, the green emissions centred at 2.53 eV are significantly enhanced with a red-shift to 2.19 eV, probably due to the changes in the charge states of the defects. Enhanced yellow-green emissions are well resolved into four peaks at around 1.98, 2.19, 2.36, and 2.53 eV due to a shallow irradiation depth. Possible origins are proposed and discussed.
文摘Reviewed are the present status and future prospects of the laser fusionresearch at the ILE Osaka. The Gekko XII and Peta Watt laser system have been operated forinvestigating the implosion hydrodynamics, fast ignition, and the relativistic laser plasmainteractions and so on. In particular, the fast ignition experiments with cone shell target havebeen in progress as the UK and US-Japan collaboration programs. In the experiments, the implodedhigh density plasmas are heated by irradiating 500 J level peta-watt laser pulse. The thermalneutron yield is found to increase by three orders of magnitude by injecting the peta-watt laserinto the cone shell target. The Rayleigh-Taylor instability experiment results are also reviewed isthis paper.
