Understanding laser induced ultrafast processes with complex three-dimensional(3D)geometries and extreme property evolution offers a unique opportunity to explore novel physical phenomena and to overcome the manufactu...Understanding laser induced ultrafast processes with complex three-dimensional(3D)geometries and extreme property evolution offers a unique opportunity to explore novel physical phenomena and to overcome the manufacturing limitations.Ultrafast imaging offers exceptional spatiotemporal resolution and thus has been considered an effective tool.However,in conventional single-view imaging techniques,3D information is projected on a two-dimensional plane,which leads to significant information loss that is detrimental to understanding the full ultrafast process.Here,we propose a quasi-3D imaging method to describe the ultrafast process and further analyze spatial asymmetries of laser induced plasma.Orthogonally polarized laser pulses are adopted to illuminate reflection-transmission views,and binarization techniques are employed to extract contours,forming the corresponding two-dimensional matrix.By rotating and multiplying the two-dimensional contour matrices obtained from the dual views,a quasi-3D image can be reconstructed.This successfully reveals dual-phase transition mechanisms and elucidates the diffraction phenomena occurring outside the plasma.Furthermore,the quasi-3D image confirms the spatial asymmetries of the picosecond plasma,which is difficult to achieve with two-dimensional images.Our findings demonstrate that quasi-3D imaging not only offers a more comprehensive understanding of plasma dynamics than previous imaging methods,but also has wide potential in revealing various complex ultrafast phenomena in related fields including strong-field physics,fluid dynamics,and cutting-edge manufacturing.展开更多
Microscale charge and energy transfer is an ultrafast process that can determine the photoelectrochemical performance of devices.However,nonlinear and nonequilibrium properties hinder our understanding of ultrafast pr...Microscale charge and energy transfer is an ultrafast process that can determine the photoelectrochemical performance of devices.However,nonlinear and nonequilibrium properties hinder our understanding of ultrafast processes;thus,the direct imaging strategy has become an effective means to uncover ultrafast charge and energy transfer processes.Due to diffraction limits of optical imaging,the obtained optical image has insufficient spatial resolution.Therefore,electron beam imaging combined with a pulse laser showing high spatial–temporal resolution has become a popular area of research,and numerous breakthroughs have been achieved in recent years.In this review,we cover three typical ultrafast electron beam imaging techniques,namely,time-resolved photoemission electron microscopy,scanning ultrafast electron microscopy,and ultrafast transmission electron microscopy,in addition to the principles and characteristics of these three techniques.Some outstanding results related to photon–electron interactions,charge carrier transport and relaxation,electron–lattice coupling,and lattice oscillation are also reviewed.In summary,ultrafast electron beam imaging with high spatial–temporal resolution and multidimensional imaging abilities can promote the fundamental under-standing of physics,chemistry,and optics,as well as guide the development of advanced semiconductors and electronics.展开更多
Ultrafast laser irradiation triggers structural transformations in diamond with broad potential across many fields.Understanding how laser energy modifies the diamond lattice is essential for achieving the intended pr...Ultrafast laser irradiation triggers structural transformations in diamond with broad potential across many fields.Understanding how laser energy modifies the diamond lattice is essential for achieving the intended properties.However,the coupled thermal and mechanical responses make it hard to clarify the transformation pathways.Herein,pump-probe imaging is used to capture surface reflectivity,while a molecular dynamics-coupled two-temperature model(MD-TTM)follows atomistic transformation,revealing thermomechanical behavior and phase transition mechanisms.At fluences below 2.28 J/cm^(2),the sp^(3)lattice damage is mainly attributed to Coulomb explosion and remains confined to only a few atomic layers.At elevated fluences,the interaction includes both Coulomb explosion and phase explosion,which not only ablate surface material but also promote notable transformation from sp^(3)to sp^(2)bonding.The surface removal initiates shock waves that propagate inward,disrupting the typical compression-to-tension evolution of the stress wave.This leads to residual stress accumulation,relaxation,and renewed buildup with increasing fluence.When the laser fluence increases from 5.05 J/cm^(2)to above 9.18 J/cm^(2),the dynamic stress rises from roughly 30 GPa to beyond 100 GPa,resulting in stacking faults and extensive lattice damage within the diamond.Because the material is removed through single-atom ejection instead of cluster flow,the surface roughness remains below 2 nm,along with a low specific contact resistivity of 3×10^(-6)Ωcm^(2)and a sheet resistance of 280Ω.The results outline a processing window that allows efficient surface removal without bulk lattice damage and demonstrate a fast,controllable single-pulse laser strategy for high-quality diamond surface engineering in microelectronic and optoelectronic applications.展开更多
文摘Understanding laser induced ultrafast processes with complex three-dimensional(3D)geometries and extreme property evolution offers a unique opportunity to explore novel physical phenomena and to overcome the manufacturing limitations.Ultrafast imaging offers exceptional spatiotemporal resolution and thus has been considered an effective tool.However,in conventional single-view imaging techniques,3D information is projected on a two-dimensional plane,which leads to significant information loss that is detrimental to understanding the full ultrafast process.Here,we propose a quasi-3D imaging method to describe the ultrafast process and further analyze spatial asymmetries of laser induced plasma.Orthogonally polarized laser pulses are adopted to illuminate reflection-transmission views,and binarization techniques are employed to extract contours,forming the corresponding two-dimensional matrix.By rotating and multiplying the two-dimensional contour matrices obtained from the dual views,a quasi-3D image can be reconstructed.This successfully reveals dual-phase transition mechanisms and elucidates the diffraction phenomena occurring outside the plasma.Furthermore,the quasi-3D image confirms the spatial asymmetries of the picosecond plasma,which is difficult to achieve with two-dimensional images.Our findings demonstrate that quasi-3D imaging not only offers a more comprehensive understanding of plasma dynamics than previous imaging methods,but also has wide potential in revealing various complex ultrafast phenomena in related fields including strong-field physics,fluid dynamics,and cutting-edge manufacturing.
文摘Microscale charge and energy transfer is an ultrafast process that can determine the photoelectrochemical performance of devices.However,nonlinear and nonequilibrium properties hinder our understanding of ultrafast processes;thus,the direct imaging strategy has become an effective means to uncover ultrafast charge and energy transfer processes.Due to diffraction limits of optical imaging,the obtained optical image has insufficient spatial resolution.Therefore,electron beam imaging combined with a pulse laser showing high spatial–temporal resolution has become a popular area of research,and numerous breakthroughs have been achieved in recent years.In this review,we cover three typical ultrafast electron beam imaging techniques,namely,time-resolved photoemission electron microscopy,scanning ultrafast electron microscopy,and ultrafast transmission electron microscopy,in addition to the principles and characteristics of these three techniques.Some outstanding results related to photon–electron interactions,charge carrier transport and relaxation,electron–lattice coupling,and lattice oscillation are also reviewed.In summary,ultrafast electron beam imaging with high spatial–temporal resolution and multidimensional imaging abilities can promote the fundamental under-standing of physics,chemistry,and optics,as well as guide the development of advanced semiconductors and electronics.
基金supported by the National Natural Science Foundation of China(Grant Nos.12525205,62501065,12305356)the Hong Kong RGC General Research Fund(Grant No.T45-406/23-R)。
文摘Ultrafast laser irradiation triggers structural transformations in diamond with broad potential across many fields.Understanding how laser energy modifies the diamond lattice is essential for achieving the intended properties.However,the coupled thermal and mechanical responses make it hard to clarify the transformation pathways.Herein,pump-probe imaging is used to capture surface reflectivity,while a molecular dynamics-coupled two-temperature model(MD-TTM)follows atomistic transformation,revealing thermomechanical behavior and phase transition mechanisms.At fluences below 2.28 J/cm^(2),the sp^(3)lattice damage is mainly attributed to Coulomb explosion and remains confined to only a few atomic layers.At elevated fluences,the interaction includes both Coulomb explosion and phase explosion,which not only ablate surface material but also promote notable transformation from sp^(3)to sp^(2)bonding.The surface removal initiates shock waves that propagate inward,disrupting the typical compression-to-tension evolution of the stress wave.This leads to residual stress accumulation,relaxation,and renewed buildup with increasing fluence.When the laser fluence increases from 5.05 J/cm^(2)to above 9.18 J/cm^(2),the dynamic stress rises from roughly 30 GPa to beyond 100 GPa,resulting in stacking faults and extensive lattice damage within the diamond.Because the material is removed through single-atom ejection instead of cluster flow,the surface roughness remains below 2 nm,along with a low specific contact resistivity of 3×10^(-6)Ωcm^(2)and a sheet resistance of 280Ω.The results outline a processing window that allows efficient surface removal without bulk lattice damage and demonstrate a fast,controllable single-pulse laser strategy for high-quality diamond surface engineering in microelectronic and optoelectronic applications.
