Radiative lifetimes of two short-lived levels （i.e. 4f^8 （TF6）6p^1/2 （6, 1/2）11/2,13/2） in Tb Ⅲ are measured by time-resolved laser-induced fluorescence （LIE） technique with a two-step excitation process. Fre...Radiative lifetimes of two short-lived levels （i.e. 4f^8 （TF6）6p^1/2 （6, 1/2）11/2,13/2） in Tb Ⅲ are measured by time-resolved laser-induced fluorescence （LIE） technique with a two-step excitation process. Free Tb Ⅲ ions are produced in a laser-induced plasma. Lifetime values are evaluated with a deconvolution procedure of the timeresolved fluorescence signal with the temporal shape of second-step excitation pulse （about 1 ns）. The lifetimes of the 4f^8 （^7F6）6p^1/2 （6, 1/2）11/2 and 4f^8（^7F6）6p^1/2 （6, 1/2）13/2 levels are determined to be 1.9 （2） and 2.0 （2）ns, respectively.展开更多
We experimentally demonstrate the recognition of positional isomers of propyl alcohol vapor through nonlinear fluorescence induced by high-intensity femtosecond laser filaments in air. By measuring characteristic fluo...We experimentally demonstrate the recognition of positional isomers of propyl alcohol vapor through nonlinear fluorescence induced by high-intensity femtosecond laser filaments in air. By measuring characteristic fluorescence of n-propyl and isopropyl alcohol vapors produced by femtosecond filament excitation, it is found that they show identical spectra, that is, those from molecular bands of CH, C2, Nit, OH and CN, while the relative intensities are different. By comparing the ratios of the CH and C2 signals, the two propyl alcohol isomers are differentiated. The different signal intensities are ascribed to different ionization potentials of the two isomer molecules, leading to different production efficiencies of fluorescing fragments.展开更多
An original idea is reviewed. When a molecule is pumped into a super-excited state, one of its decay channels is neutral dissociation. One or more of the neutral fragments will fluoresce. Hence, if a lower state of su...An original idea is reviewed. When a molecule is pumped into a super-excited state, one of its decay channels is neutral dissociation. One or more of the neutral fragments will fluoresce. Hence, if a lower state of such fluorescing fragments was populated through other channels but with a lower probability, population inversion of the fluorescing fragments would be naturally realized. This idea seems to be validated, so far, by comparing published work on three hydrocarbon molecules, CH4, C2H2, C2H4, and water vapor, H2 O. After super-excitation in a femtosecond laser filament in air mixed with these molecules, the fluorescence from the CH or OH fragments exhibits population inversion, i.e., amplified spontaneous emission was observed in the backscattering direction of the filament.展开更多
The visible and near-UV emission spectroscopy of methane （CH4） induced by a femtosecond intense laser field （800 nm, 40 fs, 1014 W/cm2） is studied. By measuring the decay profiles of the neutral fragment product ...The visible and near-UV emission spectroscopy of methane （CH4） induced by a femtosecond intense laser field （800 nm, 40 fs, 1014 W/cm2） is studied. By measuring the decay profiles of the neutral fragment product CH （A2△→X2П）, two reaction pathways, i.e., the electron-ion recombination through e- ＋ CH＋ and the direct disintegration of CH＋ are found to be responsible for populating the electronic excited states of the neutral fragment product CH, which gives rise to the photoemissions. Our results provide complementary information on previous understanding of the strong-field-induced photoemission mechanism of CH4 through neutral dissociation of superexcited states.展开更多
We demonstrate the control of neutral fragmentation of methane（CH4） induced by a Ti：sapphire intense laser pulse（800 nm, 40 fs） by using a pump–probe spectroscopy. Enhancement of the fluorescence emission from t...We demonstrate the control of neutral fragmentation of methane（CH4） induced by a Ti：sapphire intense laser pulse（800 nm, 40 fs） by using a pump–probe spectroscopy. Enhancement of the fluorescence emission from the neutral radical CH（A2Δ → X2Π） induced by the intense laser field（~1014 W/cm2） is observed when the wavelength of the probe laser pulse is tuned to 400 nm. The phenomena are explained based on excitation enhancement of the super-excited state of the parent molecule resulting in an increase in neutral dissociation of the methane molecules.展开更多
We demonstrate that the filamentation process is strongly influenced by the polarization state of the driver laser. When the laser polarization changes from linear to circular, the critical power for the self-focusing...We demonstrate that the filamentation process is strongly influenced by the polarization state of the driver laser. When the laser polarization changes from linear to circular, the critical power for the self-focusing of a Ti：Sapphire laser （800 nm, 40 fs） in air increases from about 9.6 ± 1.0 to 14.9± 1.5 GW, while the second nonlinear refractive index n2 of air decreases from 9.9 × 10-2o to 6.4 ×10-20 cm2/W. We also demonstrate that the luminescence from the neutral nitrogen molecules at 337 nm is dependent on both the laser intensity and plasma density inside the filament.展开更多
We propose a new mechanism/scheme to explain the ultrafast population inversion of molecular ions which takes place in a time scale comparable to the femtosecond laser pulse. The nonlinear pumping process including th...We propose a new mechanism/scheme to explain the ultrafast population inversion of molecular ions which takes place in a time scale comparable to the femtosecond laser pulse. The nonlinear pumping process including the pump photons and the self-generated harmonic photons of the pump laser would be responsible for building up population inversion to realize remote molecule lasers in femtosecond laser filaments in gases. It is shown that the remote laser emissions in molecular ions of gases may be a universal process in the femtosecond laser filament.展开更多
基金Supported by the Swedish Natural Science Research Council and the National Natural Science Foundation of China under No 10274025.
文摘Radiative lifetimes of two short-lived levels （i.e. 4f^8 （TF6）6p^1/2 （6, 1/2）11/2,13/2） in Tb Ⅲ are measured by time-resolved laser-induced fluorescence （LIE） technique with a two-step excitation process. Free Tb Ⅲ ions are produced in a laser-induced plasma. Lifetime values are evaluated with a deconvolution procedure of the timeresolved fluorescence signal with the temporal shape of second-step excitation pulse （about 1 ns）. The lifetimes of the 4f^8 （^7F6）6p^1/2 （6, 1/2）11/2 and 4f^8（^7F6）6p^1/2 （6, 1/2）13/2 levels are determined to be 1.9 （2） and 2.0 （2）ns, respectively.
基金Supported by the National Natural Science Foundation of China under Grant Nos 61427816 and 61235003the Research Fund for the Doctoral Program of Higher Education of China under Grant No 20130061110047the Open Fund of the State Key Laboratory of High Field Laser Physics
文摘We experimentally demonstrate the recognition of positional isomers of propyl alcohol vapor through nonlinear fluorescence induced by high-intensity femtosecond laser filaments in air. By measuring characteristic fluorescence of n-propyl and isopropyl alcohol vapors produced by femtosecond filament excitation, it is found that they show identical spectra, that is, those from molecular bands of CH, C2, Nit, OH and CN, while the relative intensities are different. By comparing the ratios of the CH and C2 signals, the two propyl alcohol isomers are differentiated. The different signal intensities are ascribed to different ionization potentials of the two isomer molecules, leading to different production efficiencies of fluorescing fragments.
基金Project supported by the Canada Research Chairs,the Natural Science and Engineering Research Council of Canada(NSERC),the FRQNT,the Canada Foundation for Innovation(CFI),the National Basic Research Program of China(Grant No.2014CB921300)the National Natural Science Foundation of China(Grant No.61235003)+1 种基金the Research Fund for the Doctoral Program of Higher Education of Chinathe Scientific Research Foundation for Returned Scholars,Ministry of Education of China
文摘An original idea is reviewed. When a molecule is pumped into a super-excited state, one of its decay channels is neutral dissociation. One or more of the neutral fragments will fluoresce. Hence, if a lower state of such fluorescing fragments was populated through other channels but with a lower probability, population inversion of the fluorescing fragments would be naturally realized. This idea seems to be validated, so far, by comparing published work on three hydrocarbon molecules, CH4, C2H2, C2H4, and water vapor, H2 O. After super-excitation in a femtosecond laser filament in air mixed with these molecules, the fluorescence from the CH or OH fragments exhibits population inversion, i.e., amplified spontaneous emission was observed in the backscattering direction of the filament.
基金partially supported by the National Natural Science Foundation of China (61427816 and 61235003)the National Basic Research Program of China (2014CB921300)+1 种基金the Research Fund for the Doctoral Program of Higher Education of Chinathe Open Fund of the State Key Laboratory of High Field Laser Physics (SIOM),Canada Research Chairs, NSERC, Femtotech and FQRNT
文摘The visible and near-UV emission spectroscopy of methane （CH4） induced by a femtosecond intense laser field （800 nm, 40 fs, 1014 W/cm2） is studied. By measuring the decay profiles of the neutral fragment product CH （A2△→X2П）, two reaction pathways, i.e., the electron-ion recombination through e- ＋ CH＋ and the direct disintegration of CH＋ are found to be responsible for populating the electronic excited states of the neutral fragment product CH, which gives rise to the photoemissions. Our results provide complementary information on previous understanding of the strong-field-induced photoemission mechanism of CH4 through neutral dissociation of superexcited states.
基金partially supported by NSERC, DRDC Valcartier, Canada Research Chairs, CIPI, CFI, Femtotech, FQRNTthe National Basic Research Program of China (Nos. 2014CB921300)+2 种基金the National Natural Science Foundation of China (No. 61235003)the Research Fund for the Doctoral Program of Higher Education of Chinathe Scientific Research Foundation for Returned Scholars, Ministry of Education of China
文摘We demonstrate the control of neutral fragmentation of methane（CH4） induced by a Ti：sapphire intense laser pulse（800 nm, 40 fs） by using a pump–probe spectroscopy. Enhancement of the fluorescence emission from the neutral radical CH（A2Δ → X2Π） induced by the intense laser field（~1014 W/cm2） is observed when the wavelength of the probe laser pulse is tuned to 400 nm. The phenomena are explained based on excitation enhancement of the super-excited state of the parent molecule resulting in an increase in neutral dissociation of the methane molecules.
基金supported in part by the National Natural Science Foundation of China(Nos.61625501,61427816,and 61235003)the National Basic Research Program of China(No.2014CB921300)+1 种基金the Open Fund of the State Key Laboratory of High Field Laser Physics(SIOM)the Program for JLU Science and Technology Innovative Research Team(JLUSTIRT)(No.2017TD-21)
文摘We demonstrate that the filamentation process is strongly influenced by the polarization state of the driver laser. When the laser polarization changes from linear to circular, the critical power for the self-focusing of a Ti：Sapphire laser （800 nm, 40 fs） in air increases from about 9.6 ± 1.0 to 14.9± 1.5 GW, while the second nonlinear refractive index n2 of air decreases from 9.9 × 10-2o to 6.4 ×10-20 cm2/W. We also demonstrate that the luminescence from the neutral nitrogen molecules at 337 nm is dependent on both the laser intensity and plasma density inside the filament.
基金supported by the financial supports from NSERC,Canada Research Chairs,CIPI,CFI,FQRNTthe National Natural Science Foundation of China(Nos.11074098,11134010,60825406,and10974213)+2 种基金NCET-09-0429,the fundamental research funds of Jilin Universitytwo grants from the Ministry of Education,Culture,Sports,Science and Technology(MEXT),Japan the Grant-in-Aid for Specially Promoted Research on Ultrafast Hydrogen Migration (No. 19002006)the Grant-in-Aid for Global COE Program for Chemistry Innovation
文摘We propose a new mechanism/scheme to explain the ultrafast population inversion of molecular ions which takes place in a time scale comparable to the femtosecond laser pulse. The nonlinear pumping process including the pump photons and the self-generated harmonic photons of the pump laser would be responsible for building up population inversion to realize remote molecule lasers in femtosecond laser filaments in gases. It is shown that the remote laser emissions in molecular ions of gases may be a universal process in the femtosecond laser filament.
