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
Accurate landslide extraction is significant for landslide disaster prevention and control.Remote sensing images have been widely used in landslide investigation,and landslide extraction methods based on deep learning...Accurate landslide extraction is significant for landslide disaster prevention and control.Remote sensing images have been widely used in landslide investigation,and landslide extraction methods based on deep learning combined with remote sensing images(such as U-Net)have received a lot of attention.However,because of the variable shape and texture features of landslides in remote sensing images,the rich spectral features,and the complexity of their surrounding features,landslide extraction using U-Net can lead to problems such as false detection and missed detection.Therefore,this study introduces the channel attention mechanism called the squeeze-and-excitation network(SENet)in the feature fusion part of U-Net;the study also constructs an attention U-Net landside extraction model combining SENet and U-Net,and uses Sentinel-2A remote sensing images for model training and validation.The extraction results are evaluated through different evaluation metrics and compared with those of two models:U-Net and U-Net Backbone(U-Net Without Skip Connection).The results show that proposed the model can effectively extract landslides based on Sentinel-2A remote sensing images with an F1 value of 87.94%,which is about 2%and 3%higher than U-Net and U-Net Backbone,respectively,with less false detection and more accurate extraction results.展开更多
We report on a systematic experimental study on the fluorescence spectra produced from a femtosecond laser filament in air under a high electric field. The electric field alone was strong enough to create corona disch...We report on a systematic experimental study on the fluorescence spectra produced from a femtosecond laser filament in air under a high electric field. The electric field alone was strong enough to create corona discharge(CD). Fluorescence spectra from neutral and ionic air molecules were measured and compared with pure high-voltage CD and pure laser filamentation(FIL). Among them, high electric field assisted laser FIL produced nitrogen fluorescence more efficiently than either pure CD or pure FIL processes. The nonlinear enhancement of fluorescence from the interaction of the laser filament and corona discharging electric field resulted in a more efficient ionization along the laser filament zone, which was confirmed by the spectroscopic measurement of both ionization-induced fluorescence and plasma-scattered 800 nm laser pulses. This is believed to be the key precursor process for filament-guided discharge.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
We report on a simultaneous generation of double white light lasers through filamentation by focusing a femtosecond laser pulse. The appearance of the two white light lasers can be controlled by tilting the focusing l...We report on a simultaneous generation of double white light lasers through filamentation by focusing a femtosecond laser pulse. The appearance of the two white light lasers can be controlled by tilting the focusing lens. The spectral bandwidth and the pulse energy of the double white light lasers were controlled by tuning laser filamenting pulse energy and polarization. Two white light lasers with pulse energies of 1.54 m J and 1.84 m J,respectively, were generated with the pump laser energy of 7.43 m J. Besides being beneficial in understanding the multiple white light lasers generation process through multiple filamentation and its control, the results are also valuable for white light laser-based applications.展开更多
Sub-picosecond chirped laser pulse-induced airflow and water condensation were investigated in a cloud chamber.The results indicate that the positively chirped sub-picosecond laser pulses generate a more uniform inten...Sub-picosecond chirped laser pulse-induced airflow and water condensation were investigated in a cloud chamber.The results indicate that the positively chirped sub-picosecond laser pulses generate a more uniform intensity distribution inside the plasma column, leading to a weaker airflow and an elliptic-shaped snow pile. The negatively chirped sub-picosecond laser pulses generate a spark-like intensity distribution inside the plasma column, which produces a wider range of airflow and a round snow pile. The amount of snow weight and the concentration of NO3-- are found to be dependent on the intensity distribution inside the plasma column. The visibly stronger plasma column generates much more snow and a higher concentration of NO3--. These experimental results provide a reference for sub-picosecond laser-induced water condensation in realistic atmospheric conditions.展开更多
We demonstrate a simple technique to filter out the continuum background in filament-induced remote breakdown spectroscopy.By inserting a polarizer before the detector,the continuum background was reduced by more than...We demonstrate a simple technique to filter out the continuum background in filament-induced remote breakdown spectroscopy.By inserting a polarizer before the detector,the continuum background was reduced by more than 42%in filament-induced breakdown spectroscopy at a distance of 3.8 m,while the fluorescence intensity of aluminum atomic lines remains constant.Supercontinuum through self-phase modulation during filamentation mainly contributes to the continuum background.The polarization-gated technique provides a simple way to remove the continuum background in filament-induced remote breakdown spectroscopy.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 Project Supported by the Open Fund of Key Laboratory of Urban Land Resources Monitoring and Simulation Ministry of Natural Resources[grant number KF-2021-06-014]the National Natural Scientific Foundation of China[grant number 42201459]+2 种基金the Central Government to Guide Local Scientific and Technological Development[grant number 22ZY1QA005]Tianyou Youth Talent Lift Program of Lanzhou Jiaotong University,Young Doctoral Fund Project of Higher Education Institutions in Gansu Province[grant number 2022QB-058]State Key Laboratory of Geo-Information Engineering and Key Laboratory of Surveying and Mapping Science and Geospatial Information Technology of MNR,CASM(2022-03-03).
文摘Accurate landslide extraction is significant for landslide disaster prevention and control.Remote sensing images have been widely used in landslide investigation,and landslide extraction methods based on deep learning combined with remote sensing images(such as U-Net)have received a lot of attention.However,because of the variable shape and texture features of landslides in remote sensing images,the rich spectral features,and the complexity of their surrounding features,landslide extraction using U-Net can lead to problems such as false detection and missed detection.Therefore,this study introduces the channel attention mechanism called the squeeze-and-excitation network(SENet)in the feature fusion part of U-Net;the study also constructs an attention U-Net landside extraction model combining SENet and U-Net,and uses Sentinel-2A remote sensing images for model training and validation.The extraction results are evaluated through different evaluation metrics and compared with those of two models:U-Net and U-Net Backbone(U-Net Without Skip Connection).The results show that proposed the model can effectively extract landslides based on Sentinel-2A remote sensing images with an F1 value of 87.94%,which is about 2%and 3%higher than U-Net and U-Net Backbone,respectively,with less false detection and more accurate extraction results.
基金supported in part by National Natural Science Foundation of China (Nos 61221064,11127901 and 11404354)the National 973 Project of China (No.2011CB808103)+2 种基金the Chinese Academy of Sciences and the State Key Laboratory of High Field Laser Physicsthe 100 Talents Program of Chinese Academy of Sciencesthe Shanghai Pujiang Program
文摘We report on a systematic experimental study on the fluorescence spectra produced from a femtosecond laser filament in air under a high electric field. The electric field alone was strong enough to create corona discharge(CD). Fluorescence spectra from neutral and ionic air molecules were measured and compared with pure high-voltage CD and pure laser filamentation(FIL). Among them, high electric field assisted laser FIL produced nitrogen fluorescence more efficiently than either pure CD or pure FIL processes. The nonlinear enhancement of fluorescence from the interaction of the laser filament and corona discharging electric field resulted in a more efficient ionization along the laser filament zone, which was confirmed by the spectroscopic measurement of both ionization-induced fluorescence and plasma-scattered 800 nm laser pulses. This is believed to be the key precursor process for filament-guided discharge.
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.
基金the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB16010400)the International Partnership Program of Chinese Academy of Sciences(No.181231KYSB20160045).
文摘We report on a simultaneous generation of double white light lasers through filamentation by focusing a femtosecond laser pulse. The appearance of the two white light lasers can be controlled by tilting the focusing lens. The spectral bandwidth and the pulse energy of the double white light lasers were controlled by tuning laser filamenting pulse energy and polarization. Two white light lasers with pulse energies of 1.54 m J and 1.84 m J,respectively, were generated with the pump laser energy of 7.43 m J. Besides being beneficial in understanding the multiple white light lasers generation process through multiple filamentation and its control, the results are also valuable for white light laser-based applications.
基金supported by the National Natural Science Foundation of China(Nos.11425418,61475167,11404354,and 61221064)the State Key Laboratory Program of the Chinese Ministry of Science and Technology
文摘Sub-picosecond chirped laser pulse-induced airflow and water condensation were investigated in a cloud chamber.The results indicate that the positively chirped sub-picosecond laser pulses generate a more uniform intensity distribution inside the plasma column, leading to a weaker airflow and an elliptic-shaped snow pile. The negatively chirped sub-picosecond laser pulses generate a spark-like intensity distribution inside the plasma column, which produces a wider range of airflow and a round snow pile. The amount of snow weight and the concentration of NO3-- are found to be dependent on the intensity distribution inside the plasma column. The visibly stronger plasma column generates much more snow and a higher concentration of NO3--. These experimental results provide a reference for sub-picosecond laser-induced water condensation in realistic atmospheric conditions.
基金supported in part by the Strategic Priority Research Program of Chinese Academy of Sciences(No.XDB16000000)the Key Project from Bureau of International Cooperation of Chinese Academy of Sciences(No.181231KYSB20160045)the 100Talents Program of Chinese Academy of Sciences
文摘We demonstrate a simple technique to filter out the continuum background in filament-induced remote breakdown spectroscopy.By inserting a polarizer before the detector,the continuum background was reduced by more than 42%in filament-induced breakdown spectroscopy at a distance of 3.8 m,while the fluorescence intensity of aluminum atomic lines remains constant.Supercontinuum through self-phase modulation during filamentation mainly contributes to the continuum background.The polarization-gated technique provides a simple way to remove the continuum background in filament-induced remote breakdown spectroscopy.
