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
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
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 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.