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
Two-photon absorption in systems with parity permits access to states that cannot be directly prepared by one-photon absorption. Here we investigate ultrafast internal conversion （IC） dynamics of furan by using this...Two-photon absorption in systems with parity permits access to states that cannot be directly prepared by one-photon absorption. Here we investigate ultrafast internal conversion （IC） dynamics of furan by using this strategy in combination with femtosecond time-resolved photoelectron imaging. The dark Rydberg S1 and bright valence S2 states are simultaneously excited by two photons of 405 nm, and then ionized by two photons of 800nm. The IC from S2 to S1 is clearly observed and extracted from the time dependence of the higher photoelectron kinetic energy （PKE） component. More importantly, the internal conversions to hot So from directly-prepared S1 and secondarily-populated S1 are unambiguously identified by the time-dependence of the lower PKE component. The average lifetime of the S2 and S1 states is measured to be 29 fs. The internal conversions of S2 to S1, S1 to hot So occur on estimated timescales of 15.4 fs and 38 fs, respectively.展开更多
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Supported by the National Natural Science Foundation of China under Grant Nos 21303255,21273274 and 91121006
文摘Two-photon absorption in systems with parity permits access to states that cannot be directly prepared by one-photon absorption. Here we investigate ultrafast internal conversion （IC） dynamics of furan by using this strategy in combination with femtosecond time-resolved photoelectron imaging. The dark Rydberg S1 and bright valence S2 states are simultaneously excited by two photons of 405 nm, and then ionized by two photons of 800nm. The IC from S2 to S1 is clearly observed and extracted from the time dependence of the higher photoelectron kinetic energy （PKE） component. More importantly, the internal conversions to hot So from directly-prepared S1 and secondarily-populated S1 are unambiguously identified by the time-dependence of the lower PKE component. The average lifetime of the S2 and S1 states is measured to be 29 fs. The internal conversions of S2 to S1, S1 to hot So occur on estimated timescales of 15.4 fs and 38 fs, respectively.
