Propagation of a signal beam in an Al Ga As/Ga As waveguide multiple-prism light deflector is theoretically investigated by solving the scalar Helmholtz equation to obtain the dependences of the temporal and spatial r...Propagation of a signal beam in an Al Ga As/Ga As waveguide multiple-prism light deflector is theoretically investigated by solving the scalar Helmholtz equation to obtain the dependences of the temporal and spatial resolvable characteristics of the ultrafast deflector on the material dispersion of Ga As including group velocity dispersion and angular dispersion,interface reflection,and interface scattering of multiple-prism deflector.Furthermore,we experimentally confirm that,in this ultrafast beam deflection device,the deflecting angle of the signal light beam is linear with the pump fluence and the temporal resolution of the ultrafast deflection is 10 ps.Our results show that the improvement of the temporal and spatial resolvable performances is possible by properly choosing the structural parameters and enhancing the quality of the device.展开更多
Understanding the ultrafast carrier dynamics and the mechanism of two-dimensional(2D)transition metal dichalcogenides(TMDs)is key to their applications in the field of optoelectronic devices.In this work,a single puls...Understanding the ultrafast carrier dynamics and the mechanism of two-dimensional(2D)transition metal dichalcogenides(TMDs)is key to their applications in the field of optoelectronic devices.In this work,a single pulse pump probe method is introduced to detect the layer-dependent ultrafast carrier dynamics of monolayer and few-layer WS_(2) excited by a femtosecond pulse.Results show that the ultrafast carrier dynamics of the layered WS_(2) films can be divided into three stages:the fast photoexcitation phase with the characteristic time of 2–4 ps,the fast decay phase with the characteristic time of 4–20 ps,and the slow decay phase lasting several hundred picoseconds.Moreover,the layer dependency of the characteristic time of each stage has been observed,and the corresponding mechanism of free carrier dynamics has been discussed.It has been observed as well that the monolayer WS_(2) exhibits a unique rising time of carriers after photoexcitation.The proposed method can be expected to be an effective approach for studying the dynamics of the photoexcited carriers in 2D TMDs.Our results provide a comprehensive understanding of the photoexcited carrier dynamics of layered WS_(2),which is essential for its application in optoelectronics and photovoltaic devices.展开更多
This paper reports that a one-colour fs pump probe measurement has been carried out for studying photoionization/photodissociation of cyclohexanone （C6H10O） in intense laser field. Two of the fragments from eyclohex...This paper reports that a one-colour fs pump probe measurement has been carried out for studying photoionization/photodissociation of cyclohexanone （C6H10O） in intense laser field. Two of the fragments from eyclohexanone, C2H＋ and C3H3＋, are studied under 800 nm laser pump-probe and the results obtained show similar time evolutions. It proposes a feasible model for analysing the experimental observations of the one-colour fs pump-probe measurement. The results demonstrate that as an intermediate product, the excited molecular parent ions play a very important role in photionization/photodissociation processes in intense laser field.展开更多
Resonance enhancement has been increasingly employed in the emergent felntosecond stimu- lated Raman spectroscopy （FSRS） to selectively monitor molecular structure and dynamics with improved spectral and temporal re...Resonance enhancement has been increasingly employed in the emergent felntosecond stimu- lated Raman spectroscopy （FSRS） to selectively monitor molecular structure and dynamics with improved spectral and temporal resolutions and signal-to-noise ratios. Such joint eflforts by the technique- and application-oriented scientists and engineers have laid the foundation for exploiting the tunable FSRS methodology to investigate a great variety of photosensitive systems and elucidate the underlying functional mechanisms on molecular time scales. Dur- ing spectral analysis, peak line shapes remain a major concern with an intricate dependence on resonance conditions. Here, we present a comprehensive study of line shapes by tuning the Rarnan pump wavelength from red to blue side of the ground-state absorption band of the fluorescent dye rhodarnine 6G in solution. Distinct line shape patterns in Stokes and anti-Stokes FSRS as well as from the low to high-frequency modes highlight the competition between multiple third-order and higher-order nonlinear pathways, governed by difl^rent res- onance conditions achieved by Raman pump and probe pulses. In particular, the resonance condition of probe wavelength is revealed to play an important role in generating circular line shape changes through oppositely phased dispersion via hot luminescence （HL） pathways. Meanwhile, on-resonance conditions of the Rarnan pump could promote excited-state vibrational modes which are broadened and red-shifted from the coincident ground-state vibrational modes, posing challenges for spectral analysis. Certain strategies in tuning the Raman pump and probe to characteristic regions across an electronic transition band are discussed to improve the FSRS usability and versatility as a powerful structural dynamics toolset to advance chemical, physical, materials, and biological sciences.展开更多
The experimental investigation of axial-flow pump has been rapidly developed to meet the needs of South-to-North Water Diversion Project of China. Owing to the boundary conditions of hub, blade tip clearance, much of ...The experimental investigation of axial-flow pump has been rapidly developed to meet the needs of South-to-North Water Diversion Project of China. Owing to the boundary conditions of hub, blade tip clearance, much of the physical phenomena and laws involved in this complex flow field can＇t be fully determined. The flow characteristics of the high efficiency axial-flow pump have been simulated by RNG k-e turbulence model and SIMPLEC arithmetic based on FLUENT software. Numerical results indicate that the data from the prediction show agreement with the experimental results, static pressure on pressure side of blades increases slightly at circumferential direction with radius increasing, and keep almost constant at the same radial while increasing gradually from inlet to exit on the suction side along flow direction at design conditions. The static pressure, total pressure and velocity at inlet, impeller outlet and vane outlet were measured by a five-hole probe, and a contrastive experiment was done to investigate the influence of hub leakage. The experimental results show that inlet flow is almost axial and the prerotation is very small at various conditions. The meridional velocity and circulation distribution are almost identical at impeller outlet at design conditions due to steady flow and high efficiency. The residual circulation exits at downstream of the guide vane, and the circumferential velocity component increases linearly from hub to tip at small flow rate conditions. Hub leakage in adjustable blades results in the decrease of the meridional velocity and circulation at blade exit near hub. The results of numerical simulation and experiments supply important flow structure information for the high-efficiency axial-flow pump.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11274377 and 61176006)the State Major Research Equipment ProChina(Grant No.ZDY2011-2)
文摘Propagation of a signal beam in an Al Ga As/Ga As waveguide multiple-prism light deflector is theoretically investigated by solving the scalar Helmholtz equation to obtain the dependences of the temporal and spatial resolvable characteristics of the ultrafast deflector on the material dispersion of Ga As including group velocity dispersion and angular dispersion,interface reflection,and interface scattering of multiple-prism deflector.Furthermore,we experimentally confirm that,in this ultrafast beam deflection device,the deflecting angle of the signal light beam is linear with the pump fluence and the temporal resolution of the ultrafast deflection is 10 ps.Our results show that the improvement of the temporal and spatial resolvable performances is possible by properly choosing the structural parameters and enhancing the quality of the device.
基金supported by the National Natural Science Foundation of China (Nos. 51975232 and 51727809)the Experiment Center for Advanced Manufacturing and Technology in the School of Mechanical Science & Engineering of HUST for the technical support.
文摘Understanding the ultrafast carrier dynamics and the mechanism of two-dimensional(2D)transition metal dichalcogenides(TMDs)is key to their applications in the field of optoelectronic devices.In this work,a single pulse pump probe method is introduced to detect the layer-dependent ultrafast carrier dynamics of monolayer and few-layer WS_(2) excited by a femtosecond pulse.Results show that the ultrafast carrier dynamics of the layered WS_(2) films can be divided into three stages:the fast photoexcitation phase with the characteristic time of 2–4 ps,the fast decay phase with the characteristic time of 4–20 ps,and the slow decay phase lasting several hundred picoseconds.Moreover,the layer dependency of the characteristic time of each stage has been observed,and the corresponding mechanism of free carrier dynamics has been discussed.It has been observed as well that the monolayer WS_(2) exhibits a unique rising time of carriers after photoexcitation.The proposed method can be expected to be an effective approach for studying the dynamics of the photoexcited carriers in 2D TMDs.Our results provide a comprehensive understanding of the photoexcited carrier dynamics of layered WS_(2),which is essential for its application in optoelectronics and photovoltaic devices.
基金Project supported by the National Natural Science Foundation of China (Grant No 10534010)
文摘This paper reports that a one-colour fs pump probe measurement has been carried out for studying photoionization/photodissociation of cyclohexanone （C6H10O） in intense laser field. Two of the fragments from eyclohexanone, C2H＋ and C3H3＋, are studied under 800 nm laser pump-probe and the results obtained show similar time evolutions. It proposes a feasible model for analysing the experimental observations of the one-colour fs pump-probe measurement. The results demonstrate that as an intermediate product, the excited molecular parent ions play a very important role in photionization/photodissociation processes in intense laser field.
基金supported by the U.S.National Science Foundation CAREER grant(CHE-1455353)the Oregon State University(OSU) Research Equipment Reserve Fund(Spring 2014)to C.Fang(USTC9603)the Wei Family Private Foundation in supporting C.Chen(USTC 0903) during his graduate studies at OSU Chemistry
文摘Resonance enhancement has been increasingly employed in the emergent felntosecond stimu- lated Raman spectroscopy （FSRS） to selectively monitor molecular structure and dynamics with improved spectral and temporal resolutions and signal-to-noise ratios. Such joint eflforts by the technique- and application-oriented scientists and engineers have laid the foundation for exploiting the tunable FSRS methodology to investigate a great variety of photosensitive systems and elucidate the underlying functional mechanisms on molecular time scales. Dur- ing spectral analysis, peak line shapes remain a major concern with an intricate dependence on resonance conditions. Here, we present a comprehensive study of line shapes by tuning the Rarnan pump wavelength from red to blue side of the ground-state absorption band of the fluorescent dye rhodarnine 6G in solution. Distinct line shape patterns in Stokes and anti-Stokes FSRS as well as from the low to high-frequency modes highlight the competition between multiple third-order and higher-order nonlinear pathways, governed by difl^rent res- onance conditions achieved by Raman pump and probe pulses. In particular, the resonance condition of probe wavelength is revealed to play an important role in generating circular line shape changes through oppositely phased dispersion via hot luminescence （HL） pathways. Meanwhile, on-resonance conditions of the Rarnan pump could promote excited-state vibrational modes which are broadened and red-shifted from the coincident ground-state vibrational modes, posing challenges for spectral analysis. Certain strategies in tuning the Raman pump and probe to characteristic regions across an electronic transition band are discussed to improve the FSRS usability and versatility as a powerful structural dynamics toolset to advance chemical, physical, materials, and biological sciences.
基金supported by National Hi-tech Research and Development Program of China (863 Program, Grant No. 2007AA05Z207)National Science and Technology Support Scheme of China (Grant No. 2008BAF34B10)Jiangsu Provincial Graduate Student Innovation Foundation of China (Grant No. CX08B_064Z)
文摘The experimental investigation of axial-flow pump has been rapidly developed to meet the needs of South-to-North Water Diversion Project of China. Owing to the boundary conditions of hub, blade tip clearance, much of the physical phenomena and laws involved in this complex flow field can＇t be fully determined. The flow characteristics of the high efficiency axial-flow pump have been simulated by RNG k-e turbulence model and SIMPLEC arithmetic based on FLUENT software. Numerical results indicate that the data from the prediction show agreement with the experimental results, static pressure on pressure side of blades increases slightly at circumferential direction with radius increasing, and keep almost constant at the same radial while increasing gradually from inlet to exit on the suction side along flow direction at design conditions. The static pressure, total pressure and velocity at inlet, impeller outlet and vane outlet were measured by a five-hole probe, and a contrastive experiment was done to investigate the influence of hub leakage. The experimental results show that inlet flow is almost axial and the prerotation is very small at various conditions. The meridional velocity and circulation distribution are almost identical at impeller outlet at design conditions due to steady flow and high efficiency. The residual circulation exits at downstream of the guide vane, and the circumferential velocity component increases linearly from hub to tip at small flow rate conditions. Hub leakage in adjustable blades results in the decrease of the meridional velocity and circulation at blade exit near hub. The results of numerical simulation and experiments supply important flow structure information for the high-efficiency axial-flow pump.
基金This work is by the National Natural Science Foundation of China(No.22203006,No.21927901,No.92261206,No.21627805,No.12174012,No.21673004,No.21821004,No.21674001,and No.21790363)Ministry of Science and Technology of China(a special talent program)and the Beijing City.
