Recent progress in ultrafast lasers,ultrafast X-rays and ultrafast electron beams has made it possible to watch the motion of atoms in real time through pumpprobe technique.In this review,we focus on how the molecular...Recent progress in ultrafast lasers,ultrafast X-rays and ultrafast electron beams has made it possible to watch the motion of atoms in real time through pumpprobe technique.In this review,we focus on how the molecular dynamics can be studied with ultrafast electron diffraction where the dynamics is initiated by a pumping laser and then probed by pulsed electron beams.This technique allows one to track the molecular dynamics with femtosecond time resolution and Angstr6m spatial resolution.We present the basic physics and latest development of this technique.Representative applications of ultrafast electron diffraction in studies of laser-induced molecular dynamics are also discussed.This table-top technique is complementary to X-ray free-electron laser and we expect it to have a strong impact in studies of chemical dynamics.展开更多
To integrate a terahertz pump into an ultrafast electron diffraction(UED)experiment has attracted much attention due to its potential to initiate and detect the structural dynamics both directly.However,the deflection...To integrate a terahertz pump into an ultrafast electron diffraction(UED)experiment has attracted much attention due to its potential to initiate and detect the structural dynamics both directly.However,the deflection of the electron probe by the electromagnetic field of the terahertz pump alters the incident angle of the electron probe on the sample,impeding it from recording structural information afterwards.In this article,we studied this issue by a theoretical simulation of the terahertz-induced deflection effect on the electron probe,and came up with several possible schemes to reduce such effect.As a result,a terahertz-pump-electron-probe UED experiment with a temporal resolution comparable to the terahertz period is realized.We also found that Me V UED was more suitable for such terahertz pump experiment.展开更多
Ultrafast electron diffraction （UED） technique has proven to be an innovative tool for providing new insights in lattice dynamics with unprecedented temporal and spatial sensitivities. In this article, we give a bri...Ultrafast electron diffraction （UED） technique has proven to be an innovative tool for providing new insights in lattice dynamics with unprecedented temporal and spatial sensitivities. In this article, we give a brief introduction of this technique using the proposed UED station in the Synergetic Extreme Condition User Facility （SECUF） as a prototype. We briefly discussed UED＇s functionality, working principle, design consideration, and main components. We also briefly reviewed several pioneer works with UED to study structure-function correlations in several research areas. With these efforts, we endeavor to raise the awareness of this tool among those researchers, who may not yet have realized the emerging opportunities offered by this technique.展开更多
The precise control of wrinkles and strain gradients in nanofilm is of significant interest due to their profound influence on electronic band structures and spin states.Here,we employ ultrafast electron diffraction(U...The precise control of wrinkles and strain gradients in nanofilm is of significant interest due to their profound influence on electronic band structures and spin states.Here,we employ ultrafast electron diffraction(UED)to study the picosecond-scale dynamics of laser-induced bending in 2H-MoTe2 thin films.展开更多
Megaelectronvolt ultrafast electron diffraction（UED） is a promising detection tool for ultrafast processes.The quality of diffraction image is determined by the transverse evolution of the probe bunch. In this paper...Megaelectronvolt ultrafast electron diffraction（UED） is a promising detection tool for ultrafast processes.The quality of diffraction image is determined by the transverse evolution of the probe bunch. In this paper, we study the contributing terms of the emittance and space charge effects to the bunch evolution in the MeV UED scheme, employing a mean-field model with an ellipsoidal distribution as well as particle tracking simulation. The small transverse dimension of the drive laser is found to be critical to improve the reciprocal resolution, exploiting both smaller emittance and larger transverse bunch size before the solenoid. The degradation of the reciprocal spatial resolution caused by the space charge effects should be carefully controlled.展开更多
Directly resolving structural changes in material on the atomic scales of time and space is desired in studies of many disciplines.Ultrafast electron diffraction(UED),which combines the temporal resolution of femtosec...Directly resolving structural changes in material on the atomic scales of time and space is desired in studies of many disciplines.Ultrafast electron diffraction(UED),which combines the temporal resolution of femtosecond-pulse laser and the spatial sensitivity of electron diffraction,is an advancing methodology serving such a goal.Here we present the design of a UED apparatus with multiple operation modes for observation of collective atomic motions in solid material of various morphologies.This multi-mode UED employs a pulsed electron beam with propagation trajectory of parallel and convergent incidences,and diffraction configurations of transmission and reflection,as well utilities of preparation and characterization of cleaned surface and adsorbates.We recorded the process of electron-phonon coupling in single crystal molybdenum ditelluride following excitation of femtosecond laser pulses,and diffraction patterns of polycrystalline graphite thin film under different settings of electron optics,to demonstrate the temporal characteristics and tunable probe spot of the built UED apparatus,respectively.展开更多
An ultrafast electron diffraction technique with both high temporal and spatial resolution has been shown to be a powerful tool to observe the material transient structural change on an atomic scale.The space charge f...An ultrafast electron diffraction technique with both high temporal and spatial resolution has been shown to be a powerful tool to observe the material transient structural change on an atomic scale.The space charge forces in a multi-electron bunch will greatly broaden the electron pulse width,and therefore limit the temporal resolution of the high brightness electron pulse.Here in this work,we design an ultrafast electron diffraction system,and utilize a radio frequency cavity to realize the ultrafast electron pulse compression.We experimentally demonstrate that the stretched electron pulse width of14.98 ps with an electron energy of 40 keV and the electron number of 1.0 ×10;can be maximally compressed to about0.61 ps for single-pulse measurement and 2.48 ps for multi-pulse measurement by using a 3.2-GHz radiofrequency cavity.We also theoretically and experimentally analyze the parameters influencing the electron pulse compression efficiency for single-and multi-pulse measurements by considering radiofrequency field time jitter,electron pulse time jitter and their relative time jitter.We suggest that increasing the electron energy or shortening the distance between the compression cavity and the streak cavity can further improve the electron pulse compression efficiency.These experimental and theoretical results are very helpful for designing the ultrafast electron diffraction experiment equipment and compressing the ultrafast electron pulse width in a future study.展开更多
A method is proposed to determine the temporal width of high-brightness radio-frequency compressed electron pulses based on cross-correlation technique involving electron bunches and laser-induced plasma. The temporal...A method is proposed to determine the temporal width of high-brightness radio-frequency compressed electron pulses based on cross-correlation technique involving electron bunches and laser-induced plasma. The temporal evolution of 2-dimensional transverse profile of ultrafast electron bunches repelled by the formed transient electric field of laser-induced plasma on a silver needle is investigated, and the pulse-width can be obtained by analyzing these time-dependent images.This approach can characterize radio-frequency compressed ultrafast electron bunches with picosecond or sub-picosecond timescale and up to 105 electron numbers.展开更多
Femtoscience offers a unique way to understand the dynamics in physics, chemistry and biology. This subject focuses on the process happening at femto-to pico-second time scale by femtosecond optical methods. Widely us...Femtoscience offers a unique way to understand the dynamics in physics, chemistry and biology. This subject focuses on the process happening at femto-to pico-second time scale by femtosecond optical methods. Widely used in chemistry it reveals chemical reactions, including bond breaking, forming, and stretching, which happens at an ultrafast time scale. Femtoscience is also important in the biological system, for example, light harvesting system and vision system. Femtoscience in physics is also widely used, but it is not studied in this paper. Instead, we report new advances in femtochemistry and femtobiology, including structural dynamics, coherent control, enzyme function dynamics and hydration in the protein system. We also introduce attosecond science, focusing on electron dynamics at an extreme short time scale.展开更多
基金The work was supported by the National Natural Science Foundation of China(No.11925505).
文摘Recent progress in ultrafast lasers,ultrafast X-rays and ultrafast electron beams has made it possible to watch the motion of atoms in real time through pumpprobe technique.In this review,we focus on how the molecular dynamics can be studied with ultrafast electron diffraction where the dynamics is initiated by a pumping laser and then probed by pulsed electron beams.This technique allows one to track the molecular dynamics with femtosecond time resolution and Angstr6m spatial resolution.We present the basic physics and latest development of this technique.Representative applications of ultrafast electron diffraction in studies of laser-induced molecular dynamics are also discussed.This table-top technique is complementary to X-ray free-electron laser and we expect it to have a strong impact in studies of chemical dynamics.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11774409,11827807,and92050106)supported by the Synergic Extreme Condition User Facility。
文摘To integrate a terahertz pump into an ultrafast electron diffraction(UED)experiment has attracted much attention due to its potential to initiate and detect the structural dynamics both directly.However,the deflection of the electron probe by the electromagnetic field of the terahertz pump alters the incident angle of the electron probe on the sample,impeding it from recording structural information afterwards.In this article,we studied this issue by a theoretical simulation of the terahertz-induced deflection effect on the electron probe,and came up with several possible schemes to reduce such effect.As a result,a terahertz-pump-electron-probe UED experiment with a temporal resolution comparable to the terahertz period is realized.We also found that Me V UED was more suitable for such terahertz pump experiment.
基金Project supported by the National Natural Science Foundation of China(Grant No.11774409)the National Basic Research Program of China(Grant No.2013CBA01501)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant Nos.XDB16010200 and XDB07030300)
文摘Ultrafast electron diffraction （UED） technique has proven to be an innovative tool for providing new insights in lattice dynamics with unprecedented temporal and spatial sensitivities. In this article, we give a brief introduction of this technique using the proposed UED station in the Synergetic Extreme Condition User Facility （SECUF） as a prototype. We briefly discussed UED＇s functionality, working principle, design consideration, and main components. We also briefly reviewed several pioneer works with UED to study structure-function correlations in several research areas. With these efforts, we endeavor to raise the awareness of this tool among those researchers, who may not yet have realized the emerging opportunities offered by this technique.
基金supported by the High-level Talent Research Start-up Project Funding of Henan Academy of Sciences(Project No.241827012)the National Natural Science Foundation of China(Grant Nos.U22A6005 and 62271450)+1 种基金the National Key Research and Development Program of China(Grant Nos.2021YFA1301502,2024YFA1408701,and 2024YFA1408403)the Synergetic Extreme Condition User Facility(SECUF,https://cstr.cn/31123.02.SECUF)。
文摘The precise control of wrinkles and strain gradients in nanofilm is of significant interest due to their profound influence on electronic band structures and spin states.Here,we employ ultrafast electron diffraction(UED)to study the picosecond-scale dynamics of laser-induced bending in 2H-MoTe2 thin films.
基金Supported by National Natural Science Foundation of China(11127507,10925523)
文摘Megaelectronvolt ultrafast electron diffraction（UED） is a promising detection tool for ultrafast processes.The quality of diffraction image is determined by the transverse evolution of the probe bunch. In this paper, we study the contributing terms of the emittance and space charge effects to the bunch evolution in the MeV UED scheme, employing a mean-field model with an ellipsoidal distribution as well as particle tracking simulation. The small transverse dimension of the drive laser is found to be critical to improve the reciprocal resolution, exploiting both smaller emittance and larger transverse bunch size before the solenoid. The degradation of the reciprocal spatial resolution caused by the space charge effects should be carefully controlled.
基金Project supported by the Director Fund of WNLO (Grant No. WNLOZZYJ1501)the Fundamental Research Funds for the Central Universities,HUST (Grant No. 2017KFXKJC001)+1 种基金the Innovation Fund of WNLOthe Fund of State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics(Grant No. T152012)
文摘Directly resolving structural changes in material on the atomic scales of time and space is desired in studies of many disciplines.Ultrafast electron diffraction(UED),which combines the temporal resolution of femtosecond-pulse laser and the spatial sensitivity of electron diffraction,is an advancing methodology serving such a goal.Here we present the design of a UED apparatus with multiple operation modes for observation of collective atomic motions in solid material of various morphologies.This multi-mode UED employs a pulsed electron beam with propagation trajectory of parallel and convergent incidences,and diffraction configurations of transmission and reflection,as well utilities of preparation and characterization of cleaned surface and adsorbates.We recorded the process of electron-phonon coupling in single crystal molybdenum ditelluride following excitation of femtosecond laser pulses,and diffraction patterns of polycrystalline graphite thin film under different settings of electron optics,to demonstrate the temporal characteristics and tunable probe spot of the built UED apparatus,respectively.
基金Project partially supported by the National Natural Science Foundation of China(Grant Nos.51132004 and 11474096)the Fund from the Science and Technology Commission of Shanghai Municipality,China(Gant No.14JC1401500)the NYU-ECNU Institute of Physics at NYU Shanghai,China
文摘An ultrafast electron diffraction technique with both high temporal and spatial resolution has been shown to be a powerful tool to observe the material transient structural change on an atomic scale.The space charge forces in a multi-electron bunch will greatly broaden the electron pulse width,and therefore limit the temporal resolution of the high brightness electron pulse.Here in this work,we design an ultrafast electron diffraction system,and utilize a radio frequency cavity to realize the ultrafast electron pulse compression.We experimentally demonstrate that the stretched electron pulse width of14.98 ps with an electron energy of 40 keV and the electron number of 1.0 ×10;can be maximally compressed to about0.61 ps for single-pulse measurement and 2.48 ps for multi-pulse measurement by using a 3.2-GHz radiofrequency cavity.We also theoretically and experimentally analyze the parameters influencing the electron pulse compression efficiency for single-and multi-pulse measurements by considering radiofrequency field time jitter,electron pulse time jitter and their relative time jitter.We suggest that increasing the electron energy or shortening the distance between the compression cavity and the streak cavity can further improve the electron pulse compression efficiency.These experimental and theoretical results are very helpful for designing the ultrafast electron diffraction experiment equipment and compressing the ultrafast electron pulse width in a future study.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11004060,11027403,and 11304224)the Shanghai Municipal Science and Technology Commission,China(Grant Nos.10XD1401800,09142200501,09ZR1409300,09JC1404700,and 10JC1404500)
文摘A method is proposed to determine the temporal width of high-brightness radio-frequency compressed electron pulses based on cross-correlation technique involving electron bunches and laser-induced plasma. The temporal evolution of 2-dimensional transverse profile of ultrafast electron bunches repelled by the formed transient electric field of laser-induced plasma on a silver needle is investigated, and the pulse-width can be obtained by analyzing these time-dependent images.This approach can characterize radio-frequency compressed ultrafast electron bunches with picosecond or sub-picosecond timescale and up to 105 electron numbers.
基金supported by the National Natural Science Foundation of China (Grant Nos.11074016,60878019,10821062,10934001 and 10828407)the National Basic Research Program of China (Grant No.2007CB307001)
文摘Femtoscience offers a unique way to understand the dynamics in physics, chemistry and biology. This subject focuses on the process happening at femto-to pico-second time scale by femtosecond optical methods. Widely used in chemistry it reveals chemical reactions, including bond breaking, forming, and stretching, which happens at an ultrafast time scale. Femtoscience is also important in the biological system, for example, light harvesting system and vision system. Femtoscience in physics is also widely used, but it is not studied in this paper. Instead, we report new advances in femtochemistry and femtobiology, including structural dynamics, coherent control, enzyme function dynamics and hydration in the protein system. We also introduce attosecond science, focusing on electron dynamics at an extreme short time scale.
