Harmonics generated by an intense femtosecond Gaussian laser pulse normally incident on a spiral-shaped thin foil target were studied. By using two-dimensional （2D） particle-in-cell （PIC） simulation, we observed e...Harmonics generated by an intense femtosecond Gaussian laser pulse normally incident on a spiral-shaped thin foil target were studied. By using two-dimensional （2D） particle-in-cell （PIC） simulation, we observed evident odd harmonics signals in the reflection direction and found that the reflected field has a helical structure determined by the target shape. This method provides a new way to generate an intense ultraviolet vortex with high-order topological charge by use of ultrahigh intense laser-driven harmonics.展开更多
We provide the first report on the harmonics generated by an intense femtosecond vector beam that ~s normally mcment on a solid target. By using 2D particle-in-cell （PIC） codes, we observe the third and the fifth ha...We provide the first report on the harmonics generated by an intense femtosecond vector beam that ~s normally mcment on a solid target. By using 2D particle-in-cell （PIC） codes, we observe the third and the fifth harmonic signals with the same vector structure as the driving beam, and obtain an attosecond vector beam pulse train. We also show that the conversion efficiencies of the third and the fifth harmonics reach their maxima for a plasma density of four times the critical density due to the plasma resonating with the driving force. This method provides a new means of generating intense extreme ultraviolet （XUV） vector beams via ultra-intense laser-driven harmonics.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
A bow shock is formed in the interaction of a high-speed laser-driven plasma cloud with a cylinder obstacle. Its temporal and spatial structures are observed by shadowgraphy and interferometry. The width of the shock ...A bow shock is formed in the interaction of a high-speed laser-driven plasma cloud with a cylinder obstacle. Its temporal and spatial structures are observed by shadowgraphy and interferometry. The width of the shock transition region is - 50 μm, comparable to the ion–ion collision mean free path, which indicates that collision is dominated in the shock probably. The Mach-number of the ablating plasma cloud is ～ 15 at first, and decreases with time resulting in a changing shock structure. A two-dimension hydrodynamics code, USim, is used to simulate the interaction process. The simulated shocks can well reproduce the observed.展开更多
We have studied the propagation dynamics of ultrafast electron pulses by using an improved mean-field model, in which the propagation of the electron pulses across the boundary of the acceleration region is explicitly...We have studied the propagation dynamics of ultrafast electron pulses by using an improved mean-field model, in which the propagation of the electron pulses across the boundary of the acceleration region is explicitly considered. A large decrease in the speed spread of the electron pulses（we called “boundary kick”） is observed and properly treated leading to a significant improvement in the simulation accuracy, particularly when the density of electrons is very large. We show that our method is consistent with the simulation by the N-particle method, while others can introduce factorial error.展开更多
基金Project supported by the National Basic Research Program of China(Grant Nos.2013CBA01501 and 2013CBA01504)the National Key Scientific Instrument and Equipment Development Project,China(Grant No.2012YQ120047)+1 种基金CAS Key Program and National Natural Science Foundation of China(Grant Nos.11135012 and 11375262)a Project of Higher Educational Science and Technology Program of Shandong Province,China(Grant No.J11LA52)
文摘Harmonics generated by an intense femtosecond Gaussian laser pulse normally incident on a spiral-shaped thin foil target were studied. By using two-dimensional （2D） particle-in-cell （PIC） simulation, we observed evident odd harmonics signals in the reflection direction and found that the reflected field has a helical structure determined by the target shape. This method provides a new way to generate an intense ultraviolet vortex with high-order topological charge by use of ultrahigh intense laser-driven harmonics.
基金supported by the National Basic Research Program of China(Grant Nos.2013CBA01501 and 2013CBA01504)the National Key Scientific Instrument and Equipment Development Project of China(Grant No.2012YQ120047)+1 种基金Chinese Academy of Science Key Program,the National Natural Science of China(Grant Nos.11135012 and 11375262)the Project of Shandong Province Higher Educational Science and Technology Program,China(Grant No.J11LA52)
文摘We provide the first report on the harmonics generated by an intense femtosecond vector beam that ~s normally mcment on a solid target. By using 2D particle-in-cell （PIC） codes, we observe the third and the fifth harmonic signals with the same vector structure as the driving beam, and obtain an attosecond vector beam pulse train. We also show that the conversion efficiencies of the third and the fifth harmonics reach their maxima for a plasma density of four times the critical density due to the plasma resonating with the driving force. This method provides a new means of generating intense extreme ultraviolet （XUV） vector beams via ultra-intense laser-driven harmonics.
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 Basic Research Program of China(Grant No.2013CBA01501)the National Natural Science Foundation of China(Grant Nos.11135012,11375262,11503041,and 11520101003)the Science Challenge Program of China(Grant No.JCKY2016212A505)
文摘A bow shock is formed in the interaction of a high-speed laser-driven plasma cloud with a cylinder obstacle. Its temporal and spatial structures are observed by shadowgraphy and interferometry. The width of the shock transition region is - 50 μm, comparable to the ion–ion collision mean free path, which indicates that collision is dominated in the shock probably. The Mach-number of the ablating plasma cloud is ～ 15 at first, and decreases with time resulting in a changing shock structure. A two-dimension hydrodynamics code, USim, is used to simulate the interaction process. The simulated shocks can well reproduce the observed.
基金Project supported by the National Basic Research Program of China(Grant No.2013CBA01501)the Science Challenge Program and the Strategic Pilot Project of the Chinese Academy of Sciences
文摘We have studied the propagation dynamics of ultrafast electron pulses by using an improved mean-field model, in which the propagation of the electron pulses across the boundary of the acceleration region is explicitly considered. A large decrease in the speed spread of the electron pulses（we called “boundary kick”） is observed and properly treated leading to a significant improvement in the simulation accuracy, particularly when the density of electrons is very large. We show that our method is consistent with the simulation by the N-particle method, while others can introduce factorial error.
