With more than 30 years of development,laser-induced fluorescence(LIF)is becoming an increasingly common diagnostic to measure ion and neutral velocity distribution functions in different fields of studies in plasma s...With more than 30 years of development,laser-induced fluorescence(LIF)is becoming an increasingly common diagnostic to measure ion and neutral velocity distribution functions in different fields of studies in plasma science including Hall thrusters,linear devices,plasma processing,and basic plasma physical processes.In this paper,technical methods used in the LIF diagnostic,including modulation,collection optics,and wavelength calibration techniques are reviewed in detail.A few basic physical processes along with applications and future development associated with the LIF diagnostics are also reviewed.展开更多
An accurate and reasonable technique combining direct absorption spectroscopy and laser-induced fluorescence（LIF）methods is developed to quantitatively measure the concentrations of hydroxyl in CH;/air flat laminar ...An accurate and reasonable technique combining direct absorption spectroscopy and laser-induced fluorescence（LIF）methods is developed to quantitatively measure the concentrations of hydroxyl in CH;/air flat laminar flame. In our approach, particular attention is paid to the linear laser-induced fluorescence and absorption processes, and experimental details as well. Through measuring the temperature, LIF signal distribution and integrated absorption, spatially absolute OH concentrations profiles are successfully resolved. These experimental results are then compared with the numerical simulation. It is proved that the good quality of the results implies that this method is suitable for calibrating the OH-PLIF measurement in a practical combustor.展开更多
The one-dimensional （1D） spatial distributions of OH absolute concentration in methane/air laminar premixed flat flame under different equivalence ratios at atmospheric pressure are investigated by using bi-directio...The one-dimensional （1D） spatial distributions of OH absolute concentration in methane/air laminar premixed flat flame under different equivalence ratios at atmospheric pressure are investigated by using bi-directional laser-induced flu- orescence （LIF） detection scheme combined with the direct absorption spectroscopy. The effective peak absorption cross section and the average temperature at a height of 2 mm above the burner are obtained by exciting absorption on the Q1（8） rotational line in the A2∑＋ （Dt = 0） ←- X2∏ （v = 0） at 309.240 nm. The measured values are 1.86×10-15 cm2 and 1719 K, respectively. Spatial filtering and frequency filtering methods of reducing noise are used to deal with the experi- mental data, and the smoothing effects are also compared using the two methods. The spatial distribution regularities of OH concentration are obtained with the equivalence ratios ranging from 0.8 to 1.3. The spatial resolution of the measured result is 84μm. Finally, a comparison is made between the experimental result of this paper and other relevant study results.展开更多
The aim of the present work is to quantitatively measure the hydroxyl radical concentration by using LIF（laserinduced fluorescence） in flame.The detailed physical models of spectral absorption lineshape broadening,c...The aim of the present work is to quantitatively measure the hydroxyl radical concentration by using LIF（laserinduced fluorescence） in flame.The detailed physical models of spectral absorption lineshape broadening,collisional transition and quenching at elevated pressure are built.The fine energy level structure of the OH molecule is illustrated to understand the process with laser-induced fluorescence emission and others in the case without radiation,which include collisional quenching,rotational energy transfer（RET）,and vibrational energy transfer（VET）.Based on these,some numerical results are achieved by simulations in order to evaluate the fluorescence yield at elevated pressure.These results are useful for understanding the real physical processes in OH-LIF technique and finding a way to calibrate the signal for quantitative measurement of OH concentration in a practical combustor.展开更多
The absolute number density of nitrogen dioxide（NO2） seeded in argon is measured with cavity-enhanced laserinduced fluorescence（CELIF） through using a pulsed laser beam for the first time. The cavity ring down（CR...The absolute number density of nitrogen dioxide（NO2） seeded in argon is measured with cavity-enhanced laserinduced fluorescence（CELIF） through using a pulsed laser beam for the first time. The cavity ring down（CRD） signal is acquired simultaneously and used for normalizing the LIF signal and determining the relationship between the measured CELIF signal and the NO2 number density. The minimum detectable NO2 density down to（3.6±0.1）10^8 cm^-3 is measured in 60 s of acquisition time by the CELIF method. The minimum absorption coefficient is measured to be（2.0±0.1）10^-9 cm^-1, corresponding to a noise equivalent absorption sensitivity of（2.2±0.1）10^9 cm.^-1Hz^-1/2. The experimental system demonstrated here can be further improved in its sensitivity and used for environmental monitoring of outdoor NO2 pollution.展开更多
Argon ion laser induced fluorescence measurements were carried out in a multipolar filament discharge with a broadband diode laser centered on 668 nm, which stimulated a transition from the metastable state in Ar（Ⅲ...Argon ion laser induced fluorescence measurements were carried out in a multipolar filament discharge with a broadband diode laser centered on 668 nm, which stimulated a transition from the metastable state in Ar（Ⅲ） 3d4F7/2 to 4p4D0 5/2. The intensity of the induced fluorescence at 442 nm was maximized by the optimization of the discharge parameters and the laser power. From the recovery of the background fluorescence after the laser was turned off, the ion diffusion coefficient was deduced and compared with the result inferred from the experiments of ion acoustic wave （IAW） damping.展开更多
A new laser induced fluorescence imaging system used for detecting and locating the petroleum pollutants is presented. A unique feature of the system was using a combination of a frequency tripled Nd:YAG pulse laser ...A new laser induced fluorescence imaging system used for detecting and locating the petroleum pollutants is presented. A unique feature of the system was using a combination of a frequency tripled Nd:YAG pulse laser and an image intensified CCD camera as imaging detector. The delay time of the system and the exposure time of the CCD are controlled by a delay generator. Petroleum pollutants on various backgrounds had been detected and located by this system. This imaging technique provides a useful noninvasive approach for the detection of petroleum pollutants, which can be used in remote sensing.展开更多
cis-1,3,4,6-Tetranitrooctahydroimidazo-[4,5 d]imidazole(BCHMX)is an advanced energetic compound that expected to spread worldwide in the near future.Since,no approved remote detection methods were reported in current ...cis-1,3,4,6-Tetranitrooctahydroimidazo-[4,5 d]imidazole(BCHMX)is an advanced energetic compound that expected to spread worldwide in the near future.Since,no approved remote detection methods were reported in current literature for this material,we performed hyper-spectral imaging and laser induced fluorescence(LIF)to a BCHMX sample under low laser fluence for determining the optimum laser wavelength used in any future BCHMX-LIF based remote detection systems.For this purpose,an experimental setup consisted of a sun spectrum lamp and hyper-spectral camera was built to illuminate and image white powder samples of BCHMX in comparison with the traditional explosives,HMX(1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane),RDX(1,3,5-trinitro-1,3,5-triazacyclohexane),PETN(2,2-Bis[(nitroxy)methyl]propane-1,3-diyldinitrate).The imaging reveals strong BCHMX sample absorption contrast among other samples at wavelength ranging from 400 to 410 nm.When light source was replaced by a 405 nm laser diode illuminator,a strong BCHMX sample LIF at the spectral range from 425 to 700 nm was observed under low laser fluence condition of 0.1 mJ/cm^(2).Finally,we demonstrated successfully the ability of the 405 nm LIF and the hyperspectral imaging technique to detect finger print traces of BCHMX on white cellulose fabric from a distance of 15 m and a detection limit of 1 mg/cm^(2).展开更多
We show that it is possible to use a single sideband to induce two-photon transparency in a three-level cascade medium. The medium simultaneously absorbs two photons as a one-step process when the middle level is far ...We show that it is possible to use a single sideband to induce two-photon transparency in a three-level cascade medium. The medium simultaneously absorbs two photons as a one-step process when the middle level is far off one-photon resonance. A resonant sideband coupling on the upper transition and the two-photon one-step process drive the medium into a trapped state, and the dominant component is the ground state. Thus almost all population is trapped in the ground state and the two-photon absorption is dramatically suppressed. We present a numerical calculation for arbitrary values of the atomic and field parameters and also provide an analytic description for the required conditions.展开更多
Jet cooled CN radical beam was formed by cold cathode DC discharge of CH3CNunder molecular beam conditions. The cylindrical cold cathode was placed between the skimmerand the nozzle to prevent the nozzle from being cl...Jet cooled CN radical beam was formed by cold cathode DC discharge of CH3CNunder molecular beam conditions. The cylindrical cold cathode was placed between the skimmerand the nozzle to prevent the nozzle from being clogged by carbon particles. The pulsed photoncounting LIF measurement was seriously jeopardized by the high intensive scattering laser lightdue to CN(B2Z)’s short lifetime (70ns) and weak fiuorescence. By using an attenuator to reducelaser intensity or a polaroid to reduce the scattering laser intensity, we obtained LIF spectra withgood S/N ratio. With the theoretical simulasd spectra, the effects of laser p0larization on LIFwere discussed and the relative populations of CN rotational and vibrational states were obtained.展开更多
基金supported by National Natural Science Foundation of China(No.11875285)。
文摘With more than 30 years of development,laser-induced fluorescence(LIF)is becoming an increasingly common diagnostic to measure ion and neutral velocity distribution functions in different fields of studies in plasma science including Hall thrusters,linear devices,plasma processing,and basic plasma physical processes.In this paper,technical methods used in the LIF diagnostic,including modulation,collection optics,and wavelength calibration techniques are reviewed in detail.A few basic physical processes along with applications and future development associated with the LIF diagnostics are also reviewed.
基金supported by the National Natural Science Foundation of China(Grant No.11272338)the Science and Technology on Scramjet Key Laboratory Funding,China(Grant No.STSKFKT 2013004)the China Scholarship Council
文摘An accurate and reasonable technique combining direct absorption spectroscopy and laser-induced fluorescence（LIF）methods is developed to quantitatively measure the concentrations of hydroxyl in CH;/air flat laminar flame. In our approach, particular attention is paid to the linear laser-induced fluorescence and absorption processes, and experimental details as well. Through measuring the temperature, LIF signal distribution and integrated absorption, spatially absolute OH concentrations profiles are successfully resolved. These experimental results are then compared with the numerical simulation. It is proved that the good quality of the results implies that this method is suitable for calibrating the OH-PLIF measurement in a practical combustor.
基金supported by the National Key Scientific Instrument and Equipment Development Projects of China(Grant No.2012YQ040164)the National Natural Science Foundation of China(Grant Nos.61275127 and 91441130)+1 种基金the China Postdoctoral Science Foundation(Grant No.2014M560262)the Postdoctoral Fellowship in Heilongjiang Province,China(Grant No.LBH-Z14074)
文摘The one-dimensional （1D） spatial distributions of OH absolute concentration in methane/air laminar premixed flat flame under different equivalence ratios at atmospheric pressure are investigated by using bi-directional laser-induced flu- orescence （LIF） detection scheme combined with the direct absorption spectroscopy. The effective peak absorption cross section and the average temperature at a height of 2 mm above the burner are obtained by exciting absorption on the Q1（8） rotational line in the A2∑＋ （Dt = 0） ←- X2∏ （v = 0） at 309.240 nm. The measured values are 1.86×10-15 cm2 and 1719 K, respectively. Spatial filtering and frequency filtering methods of reducing noise are used to deal with the experi- mental data, and the smoothing effects are also compared using the two methods. The spatial distribution regularities of OH concentration are obtained with the equivalence ratios ranging from 0.8 to 1.3. The spatial resolution of the measured result is 84μm. Finally, a comparison is made between the experimental result of this paper and other relevant study results.
基金Project supported by the National Natural Science Foundation of China(Grant No.11272338)the Fund from the Science and Technology on Scramjet Key Laboratory,China(Grant No.STSKFKT2013004)
文摘The aim of the present work is to quantitatively measure the hydroxyl radical concentration by using LIF（laserinduced fluorescence） in flame.The detailed physical models of spectral absorption lineshape broadening,collisional transition and quenching at elevated pressure are built.The fine energy level structure of the OH molecule is illustrated to understand the process with laser-induced fluorescence emission and others in the case without radiation,which include collisional quenching,rotational energy transfer（RET）,and vibrational energy transfer（VET）.Based on these,some numerical results are achieved by simulations in order to evaluate the fluorescence yield at elevated pressure.These results are useful for understanding the real physical processes in OH-LIF technique and finding a way to calibrate the signal for quantitative measurement of OH concentration in a practical combustor.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11504112,91536218,and 11604100)
文摘The absolute number density of nitrogen dioxide（NO2） seeded in argon is measured with cavity-enhanced laserinduced fluorescence（CELIF） through using a pulsed laser beam for the first time. The cavity ring down（CRD） signal is acquired simultaneously and used for normalizing the LIF signal and determining the relationship between the measured CELIF signal and the NO2 number density. The minimum detectable NO2 density down to（3.6±0.1）10^8 cm^-3 is measured in 60 s of acquisition time by the CELIF method. The minimum absorption coefficient is measured to be（2.0±0.1）10^-9 cm^-1, corresponding to a noise equivalent absorption sensitivity of（2.2±0.1）10^9 cm.^-1Hz^-1/2. The experimental system demonstrated here can be further improved in its sensitivity and used for environmental monitoring of outdoor NO2 pollution.
文摘Argon ion laser induced fluorescence measurements were carried out in a multipolar filament discharge with a broadband diode laser centered on 668 nm, which stimulated a transition from the metastable state in Ar（Ⅲ） 3d4F7/2 to 4p4D0 5/2. The intensity of the induced fluorescence at 442 nm was maximized by the optimization of the discharge parameters and the laser power. From the recovery of the background fluorescence after the laser was turned off, the ion diffusion coefficient was deduced and compared with the result inferred from the experiments of ion acoustic wave （IAW） damping.
文摘A new laser induced fluorescence imaging system used for detecting and locating the petroleum pollutants is presented. A unique feature of the system was using a combination of a frequency tripled Nd:YAG pulse laser and an image intensified CCD camera as imaging detector. The delay time of the system and the exposure time of the CCD are controlled by a delay generator. Petroleum pollutants on various backgrounds had been detected and located by this system. This imaging technique provides a useful noninvasive approach for the detection of petroleum pollutants, which can be used in remote sensing.
文摘cis-1,3,4,6-Tetranitrooctahydroimidazo-[4,5 d]imidazole(BCHMX)is an advanced energetic compound that expected to spread worldwide in the near future.Since,no approved remote detection methods were reported in current literature for this material,we performed hyper-spectral imaging and laser induced fluorescence(LIF)to a BCHMX sample under low laser fluence for determining the optimum laser wavelength used in any future BCHMX-LIF based remote detection systems.For this purpose,an experimental setup consisted of a sun spectrum lamp and hyper-spectral camera was built to illuminate and image white powder samples of BCHMX in comparison with the traditional explosives,HMX(1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane),RDX(1,3,5-trinitro-1,3,5-triazacyclohexane),PETN(2,2-Bis[(nitroxy)methyl]propane-1,3-diyldinitrate).The imaging reveals strong BCHMX sample absorption contrast among other samples at wavelength ranging from 400 to 410 nm.When light source was replaced by a 405 nm laser diode illuminator,a strong BCHMX sample LIF at the spectral range from 425 to 700 nm was observed under low laser fluence condition of 0.1 mJ/cm^(2).Finally,we demonstrated successfully the ability of the 405 nm LIF and the hyperspectral imaging technique to detect finger print traces of BCHMX on white cellulose fabric from a distance of 15 m and a detection limit of 1 mg/cm^(2).
基金Supported by National Natural Science Foundation of China under Grant Nos 60378008 and 10574052.
文摘We show that it is possible to use a single sideband to induce two-photon transparency in a three-level cascade medium. The medium simultaneously absorbs two photons as a one-step process when the middle level is far off one-photon resonance. A resonant sideband coupling on the upper transition and the two-photon one-step process drive the medium into a trapped state, and the dominant component is the ground state. Thus almost all population is trapped in the ground state and the two-photon absorption is dramatically suppressed. We present a numerical calculation for arbitrary values of the atomic and field parameters and also provide an analytic description for the required conditions.
文摘Jet cooled CN radical beam was formed by cold cathode DC discharge of CH3CNunder molecular beam conditions. The cylindrical cold cathode was placed between the skimmerand the nozzle to prevent the nozzle from being clogged by carbon particles. The pulsed photoncounting LIF measurement was seriously jeopardized by the high intensive scattering laser lightdue to CN(B2Z)’s short lifetime (70ns) and weak fiuorescence. By using an attenuator to reducelaser intensity or a polaroid to reduce the scattering laser intensity, we obtained LIF spectra withgood S/N ratio. With the theoretical simulasd spectra, the effects of laser p0larization on LIFwere discussed and the relative populations of CN rotational and vibrational states were obtained.
