We present two cavity-stabilized lasers at 1555 nm, which are built to be the frequency source for a transportable photonic microwave generation system. The frequency instability reaches the thermal noise limit （7 &#...We present two cavity-stabilized lasers at 1555 nm, which are built to be the frequency source for a transportable photonic microwave generation system. The frequency instability reaches the thermal noise limit （7 ×10-16） of the 10-cm ultra-low expansion glass cavity at 1-10s averaging time and the beat signal of the two lasers reveals a remarkable linewidth of 185mHz.展开更多
The energy transportation and accumulation effect for femtosecond(fs)laser ablation on metal targets were studied using both theoretical and experimental methods.Using finite difference method,numerical simulation of ...The energy transportation and accumulation effect for femtosecond(fs)laser ablation on metal targets were studied using both theoretical and experimental methods.Using finite difference method,numerical simulation of energy transportation characteristics on copper target ablated by femtosecond laser was performed.Energy accumulation effects on metals of silver and copper ablated by an amplified Ti:sapphire femtosecond laser system were then studied experimentally.The simulated results show that the electrons and lattices have different temperature evolvement characteristics in the ablation stage.The electron temperature increases sharply and reaches the maximum in several femtoseconds while it needs thousands of femtoseconds for lattice to reach the maximum temperature.The experimental results show that uniform laser-induced periodic surface structures(PSS)can be formed with the appropriate pulsed numbers and laser energy density.Electron-phonon coupling coefficient plays an important role in PSS formation in different metals.Surface ripples of Cu are more pronounced than those of Au under the same laser energy density.展开更多
Non-local electron transport in laser-produced plasmas under inertial confinement fusion （ICF） conditions is studied based on Fokker-Planck （FP） and hydrodynamic simulations. A comparison between the classical Spi...Non-local electron transport in laser-produced plasmas under inertial confinement fusion （ICF） conditions is studied based on Fokker-Planck （FP） and hydrodynamic simulations. A comparison between the classical Spitzer-Harm （SH） transport model and non-local transport models has been made. The result shows that among those non-local models the Epperlein and Short （ES） model of heat flux is in reasonable agreement with the FP simulation in overdense region. However, the non-local models are invalid in the hot underdense plasmas. Hydrodynamic simulation is performed with the flux limiting model and the non-local model, separately. The simulation results show that in the underdense region of the laser-produced plasmas the temperature given by the flux limiting model is significantly higher than that given with the non-local model.展开更多
Silicon junctionless nanowire transistor（JNT） is fabricated by femtosecond laser direct writing on a heavily n-doped SOI substrate.The performances of the transistor,i.e.,current drive,threshold voltage,subthreshold...Silicon junctionless nanowire transistor（JNT） is fabricated by femtosecond laser direct writing on a heavily n-doped SOI substrate.The performances of the transistor,i.e.,current drive,threshold voltage,subthreshold swing（SS）,and electron mobility are evaluated.The device shows good gate control ability and low-temperature instability in a temperature range from 10 K to 300 K.The drain currents increasing by steps with the gate voltage are clearly observed from 10 K to50 K,which is attributed to the electron transport through one-dimensional（1D） subbands formed in the nanowire.Besides,the device exhibits a better low-field electron mobility of 290 cm2·V-1·s-1,implying that the silicon nanowires fabricated by femtosecond laser have good electrical properties.This approach provides a potential application for nanoscale device patterning.展开更多
The n-ZnO/p-Si heterojunction was fabricated by depositing high quality single crystalline aluminium-doped n-type ZnO film on p-type Si using the laser molecular beam epitaxy technique. The heterojunction exhibited a ...The n-ZnO/p-Si heterojunction was fabricated by depositing high quality single crystalline aluminium-doped n-type ZnO film on p-type Si using the laser molecular beam epitaxy technique. The heterojunction exhibited a good rectifying behavior. The electrical properties of the heterojunction were investigated by means of temperature dependence current density-voltage measurements. The mechanism of the current transport was proposed based on the band structure of the heterojunction. When the applied bias V is lower than 0.15 V, the current follows the Ohmic behavior. When 0.15 V ~ V 〈 0.6 V, the transport property is dominated by diffusion or recombination in the junction space charge region, while at higher voltages （V 〉 0.6 V）, the space charge limited effect becomes the main transport mechanism. The current-voltage characteristic under illumination was also investigated. The photovoltage and the short circuit current density of the heterojunction aproached 270 mV and 2.10 mA/cm^2, respectively.展开更多
Argon ion laser induced fluorescence measurements were carried out in a multipolar filament discharge with a broadband diode laser centered on 668 nm, which stimulated a transition from the metastable state in Ar（Ⅲ...Argon ion laser induced fluorescence measurements were carried out in a multipolar filament discharge with a broadband diode laser centered on 668 nm, which stimulated a transition from the metastable state in Ar（Ⅲ） 3d4F7/2 to 4p4D0 5/2. The intensity of the induced fluorescence at 442 nm was maximized by the optimization of the discharge parameters and the laser power. From the recovery of the background fluorescence after the laser was turned off, the ion diffusion coefficient was deduced and compared with the result inferred from the experiments of ion acoustic wave （IAW） damping.展开更多
Spinal cord injury has devastating consequences because adult central nervous system （CNS） neurons do not regenerate their axons after injury. Two key reasons for axon regeneration fail- ure are extrinsic inhibitory...Spinal cord injury has devastating consequences because adult central nervous system （CNS） neurons do not regenerate their axons after injury. Two key reasons for axon regeneration fail- ure are extrinsic inhibitory factors and a low intrinsic capacity for axon regrowth. Research has therefore focused on overcom- ing extrinsic growth inhibition, and enhancing intrinsic regeneration capacity. Both of these issues will need to be addressed to enable optimal repair of the injured sp＋inal cord.展开更多
We investigate theoretically the electron transport for a two-level quantum channel （wire） with Rashba spinorbit coupling under the irradiation of a longitudinally-polarized external laser field at low temperatures....We investigate theoretically the electron transport for a two-level quantum channel （wire） with Rashba spinorbit coupling under the irradiation of a longitudinally-polarized external laser field at low temperatures. Using the method of equation of motion for Keldysh nonequilibrium Green function, we examine the time-averaged spin polarized conductance for the system with photon polarization parallel to the wire direction. By analytical analysis and a few numerical examples, the interplay effects of the external laser field and the Rashba spin-orbit coupling on the spinpolarized conductance for the system are demonstrated and discussed. It is found that the longitudinally-polarized laser field can adjust the spin polarization rate and produce some photon sideband resonances of the conductance for the system.展开更多
About φ45 mm LiAlO2 single crystal was grown by Czochralski （Cz） technique. However, the full-width at half-maximum （FWHM） value was high to 116.9 arcsec. After three vapor transport equilibration （VTE） process...About φ45 mm LiAlO2 single crystal was grown by Czochralski （Cz） technique. However, the full-width at half-maximum （FWHM） value was high to 116.9 arcsec. After three vapor transport equilibration （VTE） processes, we can obtain high-quality LiAlO2 slice with the FWHM value of 44.2 arcsec. ZnO films were fabricated on as-grown slices and after-VTE ones by pulsed laser deposition （PLD）. It was found that ZnO films on the two slices have similar crystallinity, optical transmittance and optical band gap at room temperature. These results not only show that LAO substrate is suitable for ZnO growth, but also prove that the crystal quality of LAO substrate slightly affects the structural and optical properties of ZnO film.展开更多
A Fokker-Planck code is developed based upon Epperlein＇s scheme to investigate laser-produced plasmas in relevance to inertial confinement fusion. The equations are integrated implicitly by time-splitting method. Thr...A Fokker-Planck code is developed based upon Epperlein＇s scheme to investigate laser-produced plasmas in relevance to inertial confinement fusion. The equations are integrated implicitly by time-splitting method. Three test problems are simulated to show the versatility of the code. The results are in good agreement with the existing simulations.展开更多
The physical mechanisms of Ti/Al/Ni/Au ohmic contacts to AlGaN/GaN heterostructures by laser annealing and rapid thermal annealing are systematically investigated. The microstructures indicate that a better surface mo...The physical mechanisms of Ti/Al/Ni/Au ohmic contacts to AlGaN/GaN heterostructures by laser annealing and rapid thermal annealing are systematically investigated. The microstructures indicate that a better surface morphology and an intact contact interface are formed after laser annealing. None of the TiN alloy spikes are formed at the interface of the laser annealing sample. The experimental results show that the current transport mechanism through the ohmic contact after laser annealing is different from the conventional spike mechanism, and it is dominated by thermionic field emission.展开更多
This paper describes the behaviour of impurity transport in HL-2A ohmic discharges. In 2005, small quantities of metallic impurities （A1, Ni and Ti） were successfully injected into HL-2A plasmas by laser blow-off te...This paper describes the behaviour of impurity transport in HL-2A ohmic discharges. In 2005, small quantities of metallic impurities （A1, Ni and Ti） were successfully injected into HL-2A plasmas by laser blow-off technique, and their progression was followed by the soft x-ray cameras with good spatial and temporal resolutions. The impurity confinement time is estimated from the characteristic decay time of the soft x-ray signal of the injected impurities, and it is about 30-60 ms. The transport coefficients of impurities （including diffusion coefficient and convection velocity） in radial different region have been derived by using a one-dimenslonal impurity transport code, the results present that diffusion coefficient is much smaller in the central region of plasmas than the outside of it, and it is much larger than that of neoclassical theory predictions; namely, it is anomalous.展开更多
Transient perturbation methods are most appropriate to study particle transport in tokamaks. Two most commonly used techniques of impurity injection are laser blow-off and gas puffing. Short bursts of impurities, inje...Transient perturbation methods are most appropriate to study particle transport in tokamaks. Two most commonly used techniques of impurity injection are laser blow-off and gas puffing. Short bursts of impurities, injected using the laser blow-off injection technique, are among other transient perturbation methods, undoubtedly best suited to study impurity transport The injection time and the amount of injected material can be controlled in order to study a certain phase of the discharge with a minimum perturbation of the plasma parameters. Furthermore, the source is of very short duration and thus provides an experimentally more direct measure of impurity transport.展开更多
The polarization effect introduced by electric field deformation is the most important bottleneck of CdZnTe detector in x-ray imaging. Currently, most of studies focus on electric field deformation caused by trapped c...The polarization effect introduced by electric field deformation is the most important bottleneck of CdZnTe detector in x-ray imaging. Currently, most of studies focus on electric field deformation caused by trapped carriers;the perturbation of electric field due to drifting carriers has been rarely reported. In this study, the effect of transient space-charge perturbation on carrier transport in a CdZnTe semiconductor is evaluated by using the laser-beam-induced current(LBIC) technique.Cusps appear in the current curves of CdZnTe detectors with different carrier transport performances under intense excitation, indicating the deformation of electric field. The current signals under different excitations are compared. The results suggest that with the increase of excitation, the amplitude of cusp increases and the electron transient time gradually decreases. The distortion in electric field is independent of carrier transport performance of detector. Transient space-charge perturbation is responsible for the pulse shape and affects the carrier transport process.展开更多
基金Supported by the National Natural Science Foundation of China under Grant No 91536217the West Light Foundation of the Chinese Academy of Sciences under Grant No 2013ZD02the Youth Innovation Promotion Association of the Chinese Academy of Sciences under Grant No 2015334
文摘We present two cavity-stabilized lasers at 1555 nm, which are built to be the frequency source for a transportable photonic microwave generation system. The frequency instability reaches the thermal noise limit （7 ×10-16） of the 10-cm ultra-low expansion glass cavity at 1-10s averaging time and the beat signal of the two lasers reveals a remarkable linewidth of 185mHz.
基金Project(10604017)supported by the National Natural Science Foundation of ChinaProject(Q20091303)supported by the Education Branch of Hubei Province,China
文摘The energy transportation and accumulation effect for femtosecond(fs)laser ablation on metal targets were studied using both theoretical and experimental methods.Using finite difference method,numerical simulation of energy transportation characteristics on copper target ablated by femtosecond laser was performed.Energy accumulation effects on metals of silver and copper ablated by an amplified Ti:sapphire femtosecond laser system were then studied experimentally.The simulated results show that the electrons and lattices have different temperature evolvement characteristics in the ablation stage.The electron temperature increases sharply and reaches the maximum in several femtoseconds while it needs thousands of femtoseconds for lattice to reach the maximum temperature.The experimental results show that uniform laser-induced periodic surface structures(PSS)can be formed with the appropriate pulsed numbers and laser energy density.Electron-phonon coupling coefficient plays an important role in PSS formation in different metals.Surface ripples of Cu are more pronounced than those of Au under the same laser energy density.
基金Project supported by the National Natural Science Foundation of China （Grant Nos 10375064, 10575102, 10625523）, and the National High Technology Inertial Confinement Fusion Foundation of China.
文摘Non-local electron transport in laser-produced plasmas under inertial confinement fusion （ICF） conditions is studied based on Fokker-Planck （FP） and hydrodynamic simulations. A comparison between the classical Spitzer-Harm （SH） transport model and non-local transport models has been made. The result shows that among those non-local models the Epperlein and Short （ES） model of heat flux is in reasonable agreement with the FP simulation in overdense region. However, the non-local models are invalid in the hot underdense plasmas. Hydrodynamic simulation is performed with the flux limiting model and the non-local model, separately. The simulation results show that in the underdense region of the laser-produced plasmas the temperature given by the flux limiting model is significantly higher than that given with the non-local model.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61376096,61327813,and 61404126)the National Basic Research Program of China(Grant No.2010CB934104)
文摘Silicon junctionless nanowire transistor（JNT） is fabricated by femtosecond laser direct writing on a heavily n-doped SOI substrate.The performances of the transistor,i.e.,current drive,threshold voltage,subthreshold swing（SS）,and electron mobility are evaluated.The device shows good gate control ability and low-temperature instability in a temperature range from 10 K to 300 K.The drain currents increasing by steps with the gate voltage are clearly observed from 10 K to50 K,which is attributed to the electron transport through one-dimensional（1D） subbands formed in the nanowire.Besides,the device exhibits a better low-field electron mobility of 290 cm2·V-1·s-1,implying that the silicon nanowires fabricated by femtosecond laser have good electrical properties.This approach provides a potential application for nanoscale device patterning.
基金Project supported by the Postdoctor Foundation of Hebei Province, Chinathe Natural Science Foundation of Hebei Province,China (Grant No. F2012201093)the Natural Science Foundation of Hebei University, China (Grant No. 2008127)
文摘The n-ZnO/p-Si heterojunction was fabricated by depositing high quality single crystalline aluminium-doped n-type ZnO film on p-type Si using the laser molecular beam epitaxy technique. The heterojunction exhibited a good rectifying behavior. The electrical properties of the heterojunction were investigated by means of temperature dependence current density-voltage measurements. The mechanism of the current transport was proposed based on the band structure of the heterojunction. When the applied bias V is lower than 0.15 V, the current follows the Ohmic behavior. When 0.15 V ~ V 〈 0.6 V, the transport property is dominated by diffusion or recombination in the junction space charge region, while at higher voltages （V 〉 0.6 V）, the space charge limited effect becomes the main transport mechanism. The current-voltage characteristic under illumination was also investigated. The photovoltage and the short circuit current density of the heterojunction aproached 270 mV and 2.10 mA/cm^2, respectively.
文摘Argon ion laser induced fluorescence measurements were carried out in a multipolar filament discharge with a broadband diode laser centered on 668 nm, which stimulated a transition from the metastable state in Ar（Ⅲ） 3d4F7/2 to 4p4D0 5/2. The intensity of the induced fluorescence at 442 nm was maximized by the optimization of the discharge parameters and the laser power. From the recovery of the background fluorescence after the laser was turned off, the ion diffusion coefficient was deduced and compared with the result inferred from the experiments of ion acoustic wave （IAW） damping.
基金funded by grants from the Christopher and Dana Reeve Foundation[JFC-2013(3),JFC-2013(4)]the Medical Research Council(G1000864 018556)+1 种基金the International Spinal Research Trust(Nathalie Rose Barr studentship NRB110)ERANET NEURON grant Axon Repair(013-16-002)
文摘Spinal cord injury has devastating consequences because adult central nervous system （CNS） neurons do not regenerate their axons after injury. Two key reasons for axon regeneration fail- ure are extrinsic inhibitory factors and a low intrinsic capacity for axon regrowth. Research has therefore focused on overcom- ing extrinsic growth inhibition, and enhancing intrinsic regeneration capacity. Both of these issues will need to be addressed to enable optimal repair of the injured sp＋inal cord.
基金Project supported by the National Natural Science Foundation of China （Grant No 10574042）, and the Hunan Provincial Natural Science Foundation of China （Grant No 06JJ2097）.
文摘We investigate theoretically the electron transport for a two-level quantum channel （wire） with Rashba spinorbit coupling under the irradiation of a longitudinally-polarized external laser field at low temperatures. Using the method of equation of motion for Keldysh nonequilibrium Green function, we examine the time-averaged spin polarized conductance for the system with photon polarization parallel to the wire direction. By analytical analysis and a few numerical examples, the interplay effects of the external laser field and the Rashba spin-orbit coupling on the spinpolarized conductance for the system are demonstrated and discussed. It is found that the longitudinally-polarized laser field can adjust the spin polarization rate and produce some photon sideband resonances of the conductance for the system.
文摘About φ45 mm LiAlO2 single crystal was grown by Czochralski （Cz） technique. However, the full-width at half-maximum （FWHM） value was high to 116.9 arcsec. After three vapor transport equilibration （VTE） processes, we can obtain high-quality LiAlO2 slice with the FWHM value of 44.2 arcsec. ZnO films were fabricated on as-grown slices and after-VTE ones by pulsed laser deposition （PLD）. It was found that ZnO films on the two slices have similar crystallinity, optical transmittance and optical band gap at room temperature. These results not only show that LAO substrate is suitable for ZnO growth, but also prove that the crystal quality of LAO substrate slightly affects the structural and optical properties of ZnO film.
基金National Natural Science Foundation of China(Nos.10375064,10575102,10625523)Nation High-Tech ICF Committee
文摘A Fokker-Planck code is developed based upon Epperlein＇s scheme to investigate laser-produced plasmas in relevance to inertial confinement fusion. The equations are integrated implicitly by time-splitting method. Three test problems are simulated to show the versatility of the code. The results are in good agreement with the existing simulations.
基金supported by the National Natural Science Foundation of China(Grant Nos.51577169 and 51777187)the National Key Research and Development Program of China(Grant No.2017YFB0402804)
文摘The physical mechanisms of Ti/Al/Ni/Au ohmic contacts to AlGaN/GaN heterostructures by laser annealing and rapid thermal annealing are systematically investigated. The microstructures indicate that a better surface morphology and an intact contact interface are formed after laser annealing. None of the TiN alloy spikes are formed at the interface of the laser annealing sample. The experimental results show that the current transport mechanism through the ohmic contact after laser annealing is different from the conventional spike mechanism, and it is dominated by thermionic field emission.
基金Project supported by the National Natural Science Foundation of China （Grant No 10475022）.
文摘This paper describes the behaviour of impurity transport in HL-2A ohmic discharges. In 2005, small quantities of metallic impurities （A1, Ni and Ti） were successfully injected into HL-2A plasmas by laser blow-off technique, and their progression was followed by the soft x-ray cameras with good spatial and temporal resolutions. The impurity confinement time is estimated from the characteristic decay time of the soft x-ray signal of the injected impurities, and it is about 30-60 ms. The transport coefficients of impurities （including diffusion coefficient and convection velocity） in radial different region have been derived by using a one-dimenslonal impurity transport code, the results present that diffusion coefficient is much smaller in the central region of plasmas than the outside of it, and it is much larger than that of neoclassical theory predictions; namely, it is anomalous.
文摘Transient perturbation methods are most appropriate to study particle transport in tokamaks. Two most commonly used techniques of impurity injection are laser blow-off and gas puffing. Short bursts of impurities, injected using the laser blow-off injection technique, are among other transient perturbation methods, undoubtedly best suited to study impurity transport The injection time and the amount of injected material can be controlled in order to study a certain phase of the discharge with a minimum perturbation of the plasma parameters. Furthermore, the source is of very short duration and thus provides an experimentally more direct measure of impurity transport.
基金Project supported by the National Natural Science Foundation of China(Grant No.61874089)the Fund of MIIT(Grant No.MJ-2017-F-05)+2 种基金the 111 Project of China(Grant No.B08040)the NPU Foundation for Fundamental Research,Chinathe Research Found of the State Key Laboratory of Solidification Processing(NWPU),China
文摘The polarization effect introduced by electric field deformation is the most important bottleneck of CdZnTe detector in x-ray imaging. Currently, most of studies focus on electric field deformation caused by trapped carriers;the perturbation of electric field due to drifting carriers has been rarely reported. In this study, the effect of transient space-charge perturbation on carrier transport in a CdZnTe semiconductor is evaluated by using the laser-beam-induced current(LBIC) technique.Cusps appear in the current curves of CdZnTe detectors with different carrier transport performances under intense excitation, indicating the deformation of electric field. The current signals under different excitations are compared. The results suggest that with the increase of excitation, the amplitude of cusp increases and the electron transient time gradually decreases. The distortion in electric field is independent of carrier transport performance of detector. Transient space-charge perturbation is responsible for the pulse shape and affects the carrier transport process.
