Supercontinuum(SC)light source has advanced ultrafast laser spectroscopy in condensed matter science,biology,physics,and chemistry.Compared to the frequently used photonic crystal fibers and bulk materials,femtosecond...Supercontinuum(SC)light source has advanced ultrafast laser spectroscopy in condensed matter science,biology,physics,and chemistry.Compared to the frequently used photonic crystal fibers and bulk materials,femtosecond laser filamentation in gases is damage-immune for supercontinuum generation.A bottleneck problem is the strong jitters from filament induced self-heating at kHz repetition rate level.We demonstrated stable kHz supercontinuum generation directly in air with multiple mJ level pulse energy.This was achieved by applying an external DC electric field to the air plasma filament.Beam pointing jitters of the 1 kHz air filament induced SC light were reduced by more than 2 fold.The stabilized high repetition rate laser filament offers the opportunity for stable intense SC generation and its applications in air.展开更多
The characteristics of plasmas play an important role in femtosecond laser filament-based applications.Spectroscopic analysis is used to experimentally investigate the plasma density and its temperature of the air fil...The characteristics of plasmas play an important role in femtosecond laser filament-based applications.Spectroscopic analysis is used to experimentally investigate the plasma density and its temperature of the air filament under different pulse repetition rates.In our experiments,the measured average plasma density of the filament is 1.54×10^(17)cm^(-3)and the temperature of the plasma is about 5100 K under 100 Hz pulse repetition rate.The plasma density decreases to1.43×10^(17)cm^(-3)and the temperature increases to 6230 K as the pulse repetition rate increases to 1000 Hz.The experimental observation agrees with the numerical simulation by solving the nonlinear Schr?dinger equations with repetition rate related“low density hole”correction.展开更多
As intense,ultrashort,kHz-repetition-rate laser systems become commercially available,pulse cumulative effects are critical for laser filament-based applications.In this work,the pulse repetition-rate effect on femtos...As intense,ultrashort,kHz-repetition-rate laser systems become commercially available,pulse cumulative effects are critical for laser filament-based applications.In this work,the pulse repetition-rate effect on femtosecond laser filamentation in air was investigated both numerically and experimentally.The pulse repetition-rate effect has negligible influence at the leading edge of the filament.Clear intensity enhancement from a high-repetition pulse is observed at the peak and tailing edge of the laser filament.As the repetition rate of the laser pulses increases from 100 to 1000 Hz,the length of the filament extends and the intensity inside the filament increases.A physical picture based on the pulse repetition-rate dependent‘low-density hole’effect on filamentation is proposed to explain the obtained results well.展开更多
The newly developed nonhydrostatic(NH)global spectral dynamical core is evaluated by using three-dimensional(3D)benchmark tests with/without moisture.This new dynamical core differs from the original Aladin-NH like on...The newly developed nonhydrostatic(NH)global spectral dynamical core is evaluated by using three-dimensional(3D)benchmark tests with/without moisture.This new dynamical core differs from the original Aladin-NH like one in the combined use of a dry-mass vertical coordinate and a new temperature variable,and thus,it inherently conserves the dry air mass and includes the mass sink effect associated with precipitation flux.Some 3D dry benchmark tests are first conducted,including steady state,dry baroclinic waves,mountain waves in non-sheared and sheared background flows,and a dry Held–Suarez test.The results from these test cases demonstrate that the present dynamical core is accurate and robust in applications on the sphere,especially for addressing the nonhydrostatic effects.Then,three additional moist test cases are conducted to further explore the improvement of the new dynamical core.Importantly,in contrast to the original Aladin-NH like one,the new dynamical core prefers to obtain simulated tropical cyclone with lower pressure,stronger wind speeds,and faster northward movement,which is much closer to the results from the Model for Prediction Across Scales(MPAS),and it also enhances the updrafts and provides enhanced precipitation rate in the tropics,which partially compensates the inefficient vertical transport due to the absence of the deep convection parameterization in the moist Held–Suarez test,thus demonstrating its potential value for full-physics global NH numerical weather prediction application.展开更多
Laser polarization and its intensity inside a filament core play an important role in filament-based applications.However,polarization dependent clamping intensity inside filaments has been overlooked to interpret the...Laser polarization and its intensity inside a filament core play an important role in filament-based applications.However,polarization dependent clamping intensity inside filaments has been overlooked to interpret the polarization-related filamentation phenomena.Here,we report on experimental and numerical investigations of polarization dependent clamping intensity inside a femtosecond filament in air.By adjusting the initial polarization from linear to circular,the clamping intensity is increased by 1.36 times when using a 30 cm focal length lens for filamentation.The results indicate that clamping intensity inside the filament is sensitive to laser polarization,which has to be considered to fully understand polarizationrelated phenomena.展开更多
The temporal evolutions of electron density and plasma diameter of 1 kHz femtosecond laser filament in air are experimentally investigated by utilizing a pump-probe longitudinal diffraction method.A model based on sca...The temporal evolutions of electron density and plasma diameter of 1 kHz femtosecond laser filament in air are experimentally investigated by utilizing a pump-probe longitudinal diffraction method.A model based on scalar diffraction theory is proposed to extract the spatial phase shift of the probe pulse from the diffraction patterns by the laser air plasma channel.The hydrodynamic effect on plasma evolution at 1 kHz filament is included and analyzed.The measured initial peak electron density of~10^(18)cm^(-3) in our experimental conditions decays rapidly by nearly two orders of magnitude within200 ps.Moreover,the plasma channel size rises from 90μm to 120μm as the delay time increases.The experimental observation is in agreement with numerical simulation results by solving the rate equations of the charged particles.展开更多
基金This work was supported in part by NSAF(Grant No.U2130123)the International Partnership Program of Chinese Academy of Sciences(Grant Nos.181231KYSB20200033 and 181231KYSB20200040)Shanghai Science and Technology Program(Grant No.21511105000).S.L.C.acknowledges the support of COPL,Laval University,Quebec City,Canada.We thank Dr.Hao Guo,Ms.Na Chen,Mr.Xuan Zhang,Dr.Haiyi Sun from SIOM for help in the experiments and Prof.Howard M.Milchberg from the University of Maryland for the fruitful discussions and his reading of the manuscript.
文摘Supercontinuum(SC)light source has advanced ultrafast laser spectroscopy in condensed matter science,biology,physics,and chemistry.Compared to the frequently used photonic crystal fibers and bulk materials,femtosecond laser filamentation in gases is damage-immune for supercontinuum generation.A bottleneck problem is the strong jitters from filament induced self-heating at kHz repetition rate level.We demonstrated stable kHz supercontinuum generation directly in air with multiple mJ level pulse energy.This was achieved by applying an external DC electric field to the air plasma filament.Beam pointing jitters of the 1 kHz air filament induced SC light were reduced by more than 2 fold.The stabilized high repetition rate laser filament offers the opportunity for stable intense SC generation and its applications in air.
基金in part supported by the NSAF(No.U2130123)the International Partnership Program of Chinese Academy of Sciences(Nos.181231KYSB20200033 and 181231KYSB20200040)the Shanghai Science and Technology Program(No.21511105000)。
文摘The characteristics of plasmas play an important role in femtosecond laser filament-based applications.Spectroscopic analysis is used to experimentally investigate the plasma density and its temperature of the air filament under different pulse repetition rates.In our experiments,the measured average plasma density of the filament is 1.54×10^(17)cm^(-3)and the temperature of the plasma is about 5100 K under 100 Hz pulse repetition rate.The plasma density decreases to1.43×10^(17)cm^(-3)and the temperature increases to 6230 K as the pulse repetition rate increases to 1000 Hz.The experimental observation agrees with the numerical simulation by solving the nonlinear Schr?dinger equations with repetition rate related“low density hole”correction.
基金the NSAF(No.U2130123)the International Partnership Program of the Chinese Academy of Sciences(Nos.181231KYSB20200033 and 181231KYSB20200040)the Shanghai Science and Technology Program(No.21511105000).
文摘As intense,ultrashort,kHz-repetition-rate laser systems become commercially available,pulse cumulative effects are critical for laser filament-based applications.In this work,the pulse repetition-rate effect on femtosecond laser filamentation in air was investigated both numerically and experimentally.The pulse repetition-rate effect has negligible influence at the leading edge of the filament.Clear intensity enhancement from a high-repetition pulse is observed at the peak and tailing edge of the laser filament.As the repetition rate of the laser pulses increases from 100 to 1000 Hz,the length of the filament extends and the intensity inside the filament increases.A physical picture based on the pulse repetition-rate dependent‘low-density hole’effect on filamentation is proposed to explain the obtained results well.
基金Supported by the National Natural Science Foundation of China(42275062,41875121,and 41975066).
文摘The newly developed nonhydrostatic(NH)global spectral dynamical core is evaluated by using three-dimensional(3D)benchmark tests with/without moisture.This new dynamical core differs from the original Aladin-NH like one in the combined use of a dry-mass vertical coordinate and a new temperature variable,and thus,it inherently conserves the dry air mass and includes the mass sink effect associated with precipitation flux.Some 3D dry benchmark tests are first conducted,including steady state,dry baroclinic waves,mountain waves in non-sheared and sheared background flows,and a dry Held–Suarez test.The results from these test cases demonstrate that the present dynamical core is accurate and robust in applications on the sphere,especially for addressing the nonhydrostatic effects.Then,three additional moist test cases are conducted to further explore the improvement of the new dynamical core.Importantly,in contrast to the original Aladin-NH like one,the new dynamical core prefers to obtain simulated tropical cyclone with lower pressure,stronger wind speeds,and faster northward movement,which is much closer to the results from the Model for Prediction Across Scales(MPAS),and it also enhances the updrafts and provides enhanced precipitation rate in the tropics,which partially compensates the inefficient vertical transport due to the absence of the deep convection parameterization in the moist Held–Suarez test,thus demonstrating its potential value for full-physics global NH numerical weather prediction application.
基金supported in part by the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB16010400)the International Partnership Program of Chinese Academy of Sciences(Nos.181231KYSB20160045 and 181231KYSB20200033)the support from the Russian Science Foundation(No.2149-00023)。
文摘Laser polarization and its intensity inside a filament core play an important role in filament-based applications.However,polarization dependent clamping intensity inside filaments has been overlooked to interpret the polarization-related filamentation phenomena.Here,we report on experimental and numerical investigations of polarization dependent clamping intensity inside a femtosecond filament in air.By adjusting the initial polarization from linear to circular,the clamping intensity is increased by 1.36 times when using a 30 cm focal length lens for filamentation.The results indicate that clamping intensity inside the filament is sensitive to laser polarization,which has to be considered to fully understand polarizationrelated phenomena.
基金supported in part by NSAF(No.U2130123)International Partnership Program of Chinese Academy of Sciences(Nos.181231KYSB20200033 and 181231KYSB20200040)Shanghai Science and Technology Program(No.21511105000)。
文摘The temporal evolutions of electron density and plasma diameter of 1 kHz femtosecond laser filament in air are experimentally investigated by utilizing a pump-probe longitudinal diffraction method.A model based on scalar diffraction theory is proposed to extract the spatial phase shift of the probe pulse from the diffraction patterns by the laser air plasma channel.The hydrodynamic effect on plasma evolution at 1 kHz filament is included and analyzed.The measured initial peak electron density of~10^(18)cm^(-3) in our experimental conditions decays rapidly by nearly two orders of magnitude within200 ps.Moreover,the plasma channel size rises from 90μm to 120μm as the delay time increases.The experimental observation is in agreement with numerical simulation results by solving the rate equations of the charged particles.