Remote or standoff detection of greenhouse gases,air pollutants,and biological agents with innovative ultrafast laser technology attracts growing interests in recent years.Hybrid femtosecond/picosecond coherent Raman ...Remote or standoff detection of greenhouse gases,air pollutants,and biological agents with innovative ultrafast laser technology attracts growing interests in recent years.Hybrid femtosecond/picosecond coherent Raman spectroscopy is considered as one of the most versatile techniques due to its great advantages in terms of detection sensitivity and chemical specificity.However,the simultaneous requirement for the femtosecond pump and the picosecond probe increases the complexity of optical system.Herein,we demonstrate that air lasing naturally created inside a filament can serve as an ideal light source to probe Raman coherence excited by the femtosecond pump,producing coherent Raman signal with molecular vibrational signatures.The combination of pulse self-compression effect and air lasing action during filamentation improves Raman excitation efficiency and greatly simplifies the experimental setup.The air-lasing-assisted Raman spectroscopy was applied to quantitatively detect greenhouse gases mixed in air,and it was found that the minimum detectable concentrations of CO_(2) and SF_(6) can reach 0.1%and 0.03%,respectively.The ingenious designs,especially the optimization of pump-seed delay and the choice of perpendicular polarization,ensure a high detection sensitivity and signal stability.Moreover,it is demonstrated that this method can be used for simultaneously measuring CO_(2) and SF_(6) gases and distinguishing ^(12)CO_(2) and ^(13)CO_(2).The developed scheme provides a new route for high-sensitivity standoff detection and combustion diagnosis.展开更多
We report on an experimental investigation on the dynamic decoherence process of molecular rotational wavepackets during femtosecond laser filamentation based on time-dependent mean wavelength shifts of a weak probe p...We report on an experimental investigation on the dynamic decoherence process of molecular rotational wavepackets during femtosecond laser filamentation based on time-dependent mean wavelength shifts of a weak probe pulse. Details of periodic revival structures of transient alignment can be readily obtained from the measured shifted spectra due to the periodic modulation of the molecular refractive index. Using the method, we measured decoherence lifetimes of molecular rotational wavepackets in N_2 and O_2 under different experimental conditions. Our results indicate that decoherence lifetimes of molecular rotational wavepackets are primarily determined by the relative population of rotational states in the wave packet and intermolecular collisions,rather than the focusing intensity.展开更多
Molecular ions,produced via ultrafast ionization,can be quantum emitters with the aid of resonant electronic couplings,which makes them the ideal candidates to study strong-field quantum optics.In this work,we experim...Molecular ions,produced via ultrafast ionization,can be quantum emitters with the aid of resonant electronic couplings,which makes them the ideal candidates to study strong-field quantum optics.In this work,we experimentally and numerically investigate the necessary condition for observing a collective emission arising from macroscopic quantum polarization in a population-inverted N_(2)^(+)gain system,uncovering how the individual ionic emitters proceed into a coherent collection within hundreds of femtoseconds.Our results show that for a relatively high-gain case,the collective emission behaviors can be readily initiated for all the employed triggering pulse area.However,for a low-gain case,the superradiant amplification is quenched since the building time of macroscopic interionic quantum coherence exceeds the dipole dephasing time,in which situation the seed amplification and free induction decay play an essential role.These findings not only clarify the contentious key issue regarding to the amplification mechanism of N_(2)^(+)lasing but also show the unique characteristics of ultrashort laser-induced amplification in a molecular ion system where both the microscopic and macroscopic quantum coherence might be present.展开更多
We experimentally investigate the generation of above-threshold harmonics completely from argon atoms on an excited state using mid-infrared femtosecond laser pulses. The highly nonlinear dependences of the observed s...We experimentally investigate the generation of above-threshold harmonics completely from argon atoms on an excited state using mid-infrared femtosecond laser pulses. The highly nonlinear dependences of the observed signal on the pulse energy and polarization of the probe laser pulses indicate its nonperturbative characteristic.展开更多
基金the National Natural Science Foundation of China(11822410,12034013,11734009,and 11974245)the National Key R&D Program of China(2017YFA0303701 and 2019YFA0705000)+10 种基金the Shanghai Municipal Science and Technology Major Project(2019SHZDZX01)the Program of Shanghai Academic Research Leader(20XD1424200)the Natural Science Foundation of Shanghai(19ZR1475700)the Strategic Priority Research Program of Chinese Academy of Sciences(XDB16030300)the Key Research Program of Frontier Sciences of Chinese Academy of Sciences(QYZDJ-SSW-SLH010)the Youth Innovation Promotion Association of Chinese Academy of Sciences(2018284)NSF(ECCS-1509268,and CMMI-1826078)AFOSR(FA9550-20-1-0366)partially supported by the Fundamental Research Funds for the Central Universitiesthe support from the Program for Professor of Special Appointment(Eastern Scholar)at Shanghai Institutions of Higher Learningthe support from Shandong Quancheng Scholarship(00242019024)。
基金supported by the National Natural Science Foundation of China(11822410,12034013,12074063)Key Research Program of Frontier Sciences of Chinese Academy of Sciences(QYZDJ-SSW-SLH010)+2 种基金Program of Shanghai Academic Research Leader(20XD1424200)Shanghai Municipal Science and Technology Major Project(2019SHZDZX01)Youth Innovation Promotion Association of CAS(2018284).
文摘Remote or standoff detection of greenhouse gases,air pollutants,and biological agents with innovative ultrafast laser technology attracts growing interests in recent years.Hybrid femtosecond/picosecond coherent Raman spectroscopy is considered as one of the most versatile techniques due to its great advantages in terms of detection sensitivity and chemical specificity.However,the simultaneous requirement for the femtosecond pump and the picosecond probe increases the complexity of optical system.Herein,we demonstrate that air lasing naturally created inside a filament can serve as an ideal light source to probe Raman coherence excited by the femtosecond pump,producing coherent Raman signal with molecular vibrational signatures.The combination of pulse self-compression effect and air lasing action during filamentation improves Raman excitation efficiency and greatly simplifies the experimental setup.The air-lasing-assisted Raman spectroscopy was applied to quantitatively detect greenhouse gases mixed in air,and it was found that the minimum detectable concentrations of CO_(2) and SF_(6) can reach 0.1%and 0.03%,respectively.The ingenious designs,especially the optimization of pump-seed delay and the choice of perpendicular polarization,ensure a high detection sensitivity and signal stability.Moreover,it is demonstrated that this method can be used for simultaneously measuring CO_(2) and SF_(6) gases and distinguishing ^(12)CO_(2) and ^(13)CO_(2).The developed scheme provides a new route for high-sensitivity standoff detection and combustion diagnosis.
基金supported by the National Basic Research Program of China(No.2014CB921303)the National Natural Science Foundation of China(Nos.61575211,11674340,61405220,11404357,61605227,61705034,and 11704066)+5 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(No.XDB16000000)the Key Research Program of Frontier Sciences,Chinese Academy of Sciences(No.QYZDJ-SSW-SLH010)the Shanghai Yangfan Program(No.16YF1412700)the Natural Science Foundation of Jiangxi Province(No.20171BAB211007)the Science and Technology Project of Jiangxi Provincial Education Department(Nos.GJJ160587 and GJJ160576)the Shanghai Rising-Star Program(No.17QA1404600)
文摘We report on an experimental investigation on the dynamic decoherence process of molecular rotational wavepackets during femtosecond laser filamentation based on time-dependent mean wavelength shifts of a weak probe pulse. Details of periodic revival structures of transient alignment can be readily obtained from the measured shifted spectra due to the periodic modulation of the molecular refractive index. Using the method, we measured decoherence lifetimes of molecular rotational wavepackets in N_2 and O_2 under different experimental conditions. Our results indicate that decoherence lifetimes of molecular rotational wavepackets are primarily determined by the relative population of rotational states in the wave packet and intermolecular collisions,rather than the focusing intensity.
基金Major Research Plan(91850201)National Key Research and Development Program of China(2019YFA0307703)+6 种基金National Natural Science Foundation of China(1207406312064009120340131187406611822410)Program of Shanghai Academic Research Leader(20XD1424200)Hunan Provincial Innovation Foundation for Postgraduate(CX20200035).
文摘Molecular ions,produced via ultrafast ionization,can be quantum emitters with the aid of resonant electronic couplings,which makes them the ideal candidates to study strong-field quantum optics.In this work,we experimentally and numerically investigate the necessary condition for observing a collective emission arising from macroscopic quantum polarization in a population-inverted N_(2)^(+)gain system,uncovering how the individual ionic emitters proceed into a coherent collection within hundreds of femtoseconds.Our results show that for a relatively high-gain case,the collective emission behaviors can be readily initiated for all the employed triggering pulse area.However,for a low-gain case,the superradiant amplification is quenched since the building time of macroscopic interionic quantum coherence exceeds the dipole dephasing time,in which situation the seed amplification and free induction decay play an essential role.These findings not only clarify the contentious key issue regarding to the amplification mechanism of N_(2)^(+)lasing but also show the unique characteristics of ultrashort laser-induced amplification in a molecular ion system where both the microscopic and macroscopic quantum coherence might be present.
基金supported by the National Basic Research Program of China (No. 2014CB921300)the National Natural Science Foundation of China (Nos. 11127901, 11134010, 61575211, 11304330, 11404357, 61405220, 61605227, and 61705034)the Shanghai ‘Yang Fan’ Program (Nos. 14YF1406100 and 16YF1412700)
文摘We experimentally investigate the generation of above-threshold harmonics completely from argon atoms on an excited state using mid-infrared femtosecond laser pulses. The highly nonlinear dependences of the observed signal on the pulse energy and polarization of the probe laser pulses indicate its nonperturbative characteristic.
