Laser-induced fluorescence(LIF)spectroscopy is employed for plasma diagnosis,necessitating the utilization of deconvolution algorithms to isolate the Doppler effect from the raw spectral signal.However,direct deconvol...Laser-induced fluorescence(LIF)spectroscopy is employed for plasma diagnosis,necessitating the utilization of deconvolution algorithms to isolate the Doppler effect from the raw spectral signal.However,direct deconvolution becomes invalid in the presence of noise as it leads to infinite amplification of high-frequency noise components.To address this issue,we propose a deconvolution algorithm based on the maximum entropy principle.We validate the effectiveness of the proposed algorithm by utilizing simulated LIF spectra at various noise levels(signal-to-noise ratio,SNR=20–80 d B)and measured LIF spectra with Xe as the working fluid.In the typical measured spectrum(SNR=26.23 d B)experiment,compared with the Gaussian filter and the Richardson–Lucy(R-L)algorithm,the proposed algorithm demonstrates an increase in SNR of 1.39 d B and 4.66 d B,respectively,along with a reduction in the root-meansquare error(RMSE)of 35%and 64%,respectively.Additionally,there is a decrease in the spectral angle(SA)of 0.05 and 0.11,respectively.In the high-quality spectrum(SNR=43.96 d B)experiment,the results show that the running time of the proposed algorithm is reduced by about98%compared with the R-L iterative algorithm.Moreover,the maximum entropy algorithm avoids parameter optimization settings and is more suitable for automatic implementation.In conclusion,the proposed algorithm can accurately resolve Doppler spectrum details while effectively suppressing noise,thus highlighting its advantage in LIF spectral deconvolution applications.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
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 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
To measure the equivalent ratio distribution of the two-stage lean premixed(DLP)flame,we propose using acetone/toluene planar laser-induced fluorescence(PLIF)technology to simultaneously measure the concentrations of ...To measure the equivalent ratio distribution of the two-stage lean premixed(DLP)flame,we propose using acetone/toluene planar laser-induced fluorescence(PLIF)technology to simultaneously measure the concentrations of the two components.Appropriate excitation laser wavelength and filters are used to assess the influence of acetone and toluene on each other’s fluorescence signal at room temperature.Experimental results show that acetone has a strong absorption effect on toluene’s fluorescence signal,the effective absorption cross-section is 5.77×10-20 cm-2.Acetone has an obvious quenching effect on the toluene fluorescence signal,and the Stern–Volmer coefficient is 0.50 kPa-1.The collisions between the molecules of toluene and acetone will lead to the enhancement of the fluorescence signal of acetone,and the enhancement coefficient is exponential with the acetone’s concentration.The quantitative relationship between the fluorescence intensity and the concentrations of the two tracers is obtained by establishing the photophysical model of toluene and acetone’s fluorescence signals.展开更多
In this paper the OH radicals produced by a needle-plate negative DC discharge in water vapor,N_(2)+H_(2)O mixture gas and He+H_(2)O mixture gas are investigated by a laser-induced fluorescence(LIF)system.With a balla...In this paper the OH radicals produced by a needle-plate negative DC discharge in water vapor,N_(2)+H_(2)O mixture gas and He+H_(2)O mixture gas are investigated by a laser-induced fluorescence(LIF)system.With a ballast resistor in the circuit,the discharge current is limited and the discharges remain in glow.The OH rotation temperature is obtained from fluorescence rotational branch fitting,and is about 350 K in pure water vapor.The effects of the discharge current and gas pressure on the production and quenching processes of OH radicals are investigated.The results show that in water vapor and He+H_(2)O mixture gas the fluorescence intensity of OH stays nearly constant with increasing discharge current,and in N_(2)+H_(2)O mixture gas the fluorescence intensity of OH increases with increasing discharge current.In water vapor and N_(2)+H_(2)O mixture gas the fluorescence intensity of OH decreases with increasing gas pressure in the studied pressure range,and in He+H_(2)O mixture gas the fluorescence intensity of OH shows a maximum value within the studied gas pressure range.The physicochemical reactions between electrons,radicals,ground and metastable molecules are discussed.The results in this work contribute to the optimization of plasma reactivity and the establishment of a molecule reaction dynamics model.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
The effects of temperature and pressure on laser-induced fluorescence(LIF)of OH are numerically studied under the excitation of A-X(1,0)transition at high pressures.A detailed theoretical analysis is carried out to re...The effects of temperature and pressure on laser-induced fluorescence(LIF)of OH are numerically studied under the excitation of A-X(1,0)transition at high pressures.A detailed theoretical analysis is carried out to reveal the physical processes of LIF.It is shown that high pressure LIF measurements get greatly complicated by the variations of pressure-and temperature-dependent parameters,such as Boltzmann fraction,absorption lineshape broadening,central-frequency shifting,and collisional quenching.Operations at high pressures require a careful choice of an excitation line,and the Q1(8)line in the A-X(1,0)band of OH is selected due to its minimum temperature dependence through the calculation of Boltzmann fraction.The absorption spectra of OH become much broader as pressure increases,leading to a smaller overlap integral and thus smaller excitation efficiency.The central-frequency shifting cannot be omitted at high pressures,and should be taken into account when setting the excitation frequency.The fluorescence yield is estimated based on the LASKIN calculation.Finally,OH-LIF measurements were conducted on flat stoichiometric CH4/air flames at high pressures.And both the numerical and experimental results illustrate that the pressure dependence of fluorescence yield is dominated,and the fluorescence yield is approximately inversely proportional to pressure.These results illustrate the physical processes of OH-LIF and provide useful guidelines for high-pressure application of OH-LIF.展开更多
Non-intrusive characterization of the singly ionized xenon velocity in Hall thruster plume using laser induced fluorescence(LIF)is critical for constructing a complete picture of plume plasma,deeply understanding the ...Non-intrusive characterization of the singly ionized xenon velocity in Hall thruster plume using laser induced fluorescence(LIF)is critical for constructing a complete picture of plume plasma,deeply understanding the ion dynamics in the plume,and providing validation data for numerical simulation.This work presents LIF measurements of singly ionized xenon axial velocity on a grid ranging from 100 to 300 mm in axial direction and from 0 to 50 mm in radial direction for a600 W Hall thruster operating at the nominal condition of discharge voltage 300 V and discharge current 2 A,the influence of discharge voltage is investigated as well.The ion velocity distribution function(IVDF)results in the far-field plume demonstrate a profile of bimodal IVDFs,especially prominent at radial distances greater than channel inner radius of 22 mm at axial position of 100 mm,which is quite different from that of the near-field plume where bimodal IVDFs occur in the central core region for the same power Hall thruster when compared to previous LIF measurements of BHT-600 by Hargus(2010 J.Propulsion Power 26135).Beyond 100 mm,only single-peak IVDFs are measured.The two-dimensional ion velocity vector field indicates the bimodal axial IVDF is merely a geometry effect for the annular discharge channel in the far-field plume.Results about the IVDF,the most probable velocity and the accelerating potential profile along the centerline all indicate that ions are still accelerating at axial distances greater than 100 mm,and the maximum most probable velocity measured at300 mm downstream of the exit plane is about 19 km s-1.In addition,the most probable velocity of ions along radial direction changes a little except the lower velocity ion populations in the bimodal IVDF cases.The ion temperature at axial distances of 10 and 300 mm oscillates along the radial direction,while the ion temperature first increases,and then decreases for the 200 mm case.Finally,the axial position for the ion peak axial velocity on the thruster centerline is shifted upstream for higher discharge voltages,and the velocity curve is becoming steeper with the discharge voltage before reaching the maximum.This observation can be used as a criterion to optimize the thruster performance.展开更多
As a model molecule of actinide chemistry,UO molecule plays an important role in understanding the electronic structure and chemical bonding of actinide-containing species.We report a study of the laser-induced fluore...As a model molecule of actinide chemistry,UO molecule plays an important role in understanding the electronic structure and chemical bonding of actinide-containing species.We report a study of the laser-induced fluorescence spectra of the U^(16)O and U^(18)O using two-dimensional spectroscopy.Several rotationally resolved excitation spectra were investigated.Accurate molecular rotational constants and equilibrium internuclear distances were reported.Low-lying electronic states information was extracted from high resolution dispersed fluorescence spectra and analyzed by the ligand field theory model.The configuration of the ground state was determined as U^(2+)(5 f^(3)7 s)O^(2-).The branching ratios,and the vibrational harmonic and anharmonic parameters were also obtained.Radiative lifetimes were determined by recording the timeresolved fluorescence spectroscopy.Transition dipole moments were calculated using the branching ratios and the radiative lifetimes.These findings were elucidated by using quantum-chemical calculations,and the chemical bonding was also analyzed.The findings presented in this work will enrich our understanding of actinide-containing molecules.展开更多
The detection of manganese(Mn)in steel by laser-induced breakdown spectroscopy(LIBS)provides essential information for steelmaking.However,self-absorption greatly disrupts the LIBS spectral lines of Mn with high conte...The detection of manganese(Mn)in steel by laser-induced breakdown spectroscopy(LIBS)provides essential information for steelmaking.However,self-absorption greatly disrupts the LIBS spectral lines of Mn with high content.In this study,to minimize self-absorption for Mn spectral lines in LIBS,laser-induced fluorescence(LIF)was applied.Compared with conventional LIBS,the self-absorption factors(α)of Mn I 403.08,403.31,and 403.45 nm lines were reduced by 90%,88%,and 88%,respectively;the root mean square errors of crossvalidation were decreased by 88%,85%,and 87%,respectively;the average relative errors were reduced by 93%,90%,and 91%,respectively;and average relative standard deviations were decreased by 29%,32%,and 33%,respectively.The LIBS-LIF was shown to successfully minimize the self-absorption effect and spectral intensity fluctuation and improve detection accuracy.展开更多
Bay-site carboxyl functionalized perylene diimide derivative 1,7-COOH-PDI-C_(12)(PDI-COOH)was synthesized and distinct enhanced fluorescence was observed through combining with calcium ion(Ca^(2+))in THF/H_(2)O soluti...Bay-site carboxyl functionalized perylene diimide derivative 1,7-COOH-PDI-C_(12)(PDI-COOH)was synthesized and distinct enhanced fluorescence was observed through combining with calcium ion(Ca^(2+))in THF/H_(2)O solution.The assembly and fluorescence behavior of PDI-COOH/Ca^(2+)were studied in detail by changing hydration state with different concentrations.Based on the differences in assembly morphology and stoichiometric ratios of PDICOOH/Ca^(2+),we proposed the fluorescence emission mechanism of PDI-COOH/Ca^(2+)in THF/H_(2)O and THF,respectively.This work reveals a novel strategy of aggregated state fluorescence enhancement and reminds us of the important role of water in molecular fluorescence emission and assembly.展开更多
Although laser-induced breakdown spectroscopy(LIBS),as a fast on-line analysis technology,has great potential and competitiveness in the analysis of chemical composition and proximate analysis results of coal in therm...Although laser-induced breakdown spectroscopy(LIBS),as a fast on-line analysis technology,has great potential and competitiveness in the analysis of chemical composition and proximate analysis results of coal in thermal power plants,the measurement repeatability of LIBS needs to be further improved due to the difficulty in controlling the stability of the generated plasmas at present.In this paper,we propose a novel x-ray fluorescence(XRF) assisted LIBS method for high repeatability analysis of coal quality,which not only inherits the ability of LIBS to directly analyze organic elements such as C and H in coal,but also uses XRF to make up for the lack of stability of LIBS in determining other inorganic ash-forming elements.With the combination of elemental lines in LIBS and XRF spectra,the principal component analysis and the partial least squares are used to establish the prediction model and perform multi-elemental and proximate analysis of coal.Quantitative analysis results show that the relative standard deviation(RSD) of C is 0.15%,the RSDs of other elements are less than 4%,and the standard deviations of calorific value,ash content,sulfur content and volatile matter are 0.11 MJ kg,0.17%,0.79% and 0.41%respectively,indicating that the method has good repeatability in determination of coal quality.This work is helpful to accelerate the development of LIBS in the field of rapid measurement of coal entering the power plant and on-line monitoring of coal entering the furnace.展开更多
By means of one photon absorption laser-induced resonance fluorescence at 599.5 nm the relative concentrations of amidogen(NH_(2))radical in the ammonia(NH_(3))radio-frequency(rf)plasma source were measured under diff...By means of one photon absorption laser-induced resonance fluorescence at 599.5 nm the relative concentrations of amidogen(NH_(2))radical in the ammonia(NH_(3))radio-frequency(rf)plasma source were measured under different discharge pressures and rf powers.The time dependence of the fluorescence which comes from the radiation 101-211 of the P-branches of the Σ vibronic sub-bands can be described by a single-exponential decay.The decay time of NH_(2)(A2A1)Σ(0,9,0)rovibronic state was determined.The spatial dependence of the NH_(2) density in discharge tube was measured.展开更多
Femtosecond laser-induced periodic surface structures(LIPSS)have been extensively studied over the past few decades.In particular,the period and groove width of high-spatial-frequency LIPSS(HSFL)is much smaller than t...Femtosecond laser-induced periodic surface structures(LIPSS)have been extensively studied over the past few decades.In particular,the period and groove width of high-spatial-frequency LIPSS(HSFL)is much smaller than the diffraction limit,making it a useful method for efficient nanomanufacturing.However,compared with the low-spatial-frequency LIPSS(LSFL),the structure size of the HSFL is smaller,and it is more easily submerged.Therefore,the formation mechanism of HSFL is complex and has always been a research hotspot in this field.In this study,regular LSFL with a period of 760 nm was fabricated in advance on a silicon surface with two-beam interference using an 800 nm,50 fs femtosecond laser.The ultrafast dynamics of HSFL formation on the silicon surface of prefabricated LSFL under single femtosecond laser pulse irradiation were observed and analyzed for the first time using collinear pump-probe imaging method.In general,the evolution of the surface structure undergoes five sequential stages:the LSFL begins to split,becomes uniform HSFL,degenerates into an irregular LSFL,undergoes secondary splitting into a weakly uniform HSFL,and evolves into an irregular LSFL or is submerged.The results indicate that the local enhancement of the submerged nanocavity,or the nanoplasma,in the prefabricated LSFL ridge led to the splitting of the LSFL,and the thermodynamic effect drove the homogenization of the splitting LSFL,which evolved into HSFL.展开更多
Laser-induced breakdown spectroscopy(LIBS)has become a widely used atomic spectroscopic technique for rapid coal analysis.However,the vast amount of spectral information in LIBS contains signal uncertainty,which can a...Laser-induced breakdown spectroscopy(LIBS)has become a widely used atomic spectroscopic technique for rapid coal analysis.However,the vast amount of spectral information in LIBS contains signal uncertainty,which can affect its quantification performance.In this work,we propose a hybrid variable selection method to improve the performance of LIBS quantification.Important variables are first identified using Pearson's correlation coefficient,mutual information,least absolute shrinkage and selection operator(LASSO)and random forest,and then filtered and combined with empirical variables related to fingerprint elements of coal ash content.Subsequently,these variables are fed into a partial least squares regression(PLSR).Additionally,in some models,certain variables unrelated to ash content are removed manually to study the impact of variable deselection on model performance.The proposed hybrid strategy was tested on three LIBS datasets for quantitative analysis of coal ash content and compared with the corresponding data-driven baseline method.It is significantly better than the variable selection only method based on empirical knowledge and in most cases outperforms the baseline method.The results showed that on all three datasets the hybrid strategy for variable selection combining empirical knowledge and data-driven algorithms achieved the lowest root mean square error of prediction(RMSEP)values of 1.605,3.478 and 1.647,respectively,which were significantly lower than those obtained from multiple linear regression using only 12 empirical variables,which are 1.959,3.718 and 2.181,respectively.The LASSO-PLSR model with empirical support and 20 selected variables exhibited a significantly improved performance after variable deselection,with RMSEP values dropping from 1.635,3.962 and 1.647 to 1.483,3.086 and 1.567,respectively.Such results demonstrate that using empirical knowledge as a support for datadriven variable selection can be a viable approach to improve the accuracy and reliability of LIBS quantification.展开更多
Taking three typical soft samples prepared respectively by loose packings of 77-,95-,and 109-μm copper grains as examples,we perform an experiment to investigate the energy-dependent laser-induced breakdown spectrosc...Taking three typical soft samples prepared respectively by loose packings of 77-,95-,and 109-μm copper grains as examples,we perform an experiment to investigate the energy-dependent laser-induced breakdown spectroscopy(LIBS)of soft materials.We discovered a reversal phenomenon in the trend of energy dependence of plasma emission intensity:increasing initially and then decreasing separated by a well-defined critical energy.The trend reversal is attributed to the laser-induced recoil pressure at the critical energy just matching the sample's yield strength.As a result,a one-to-one correspondence can be well established between the samples'yield stress and the critical energy that is easily obtainable from LIBS measurements.This allows us to propose an innovative method for estimating the yield stress of soft materials via LIBS with attractive advantages including in-situ remote detection,real-time data collection,and minimal destructive to sample.展开更多
With the rapid advancement of laser decontamination technology and growing awareness of microbial hazards,it becomes crucial to employ theoretical model to simulate and evaluate decontamination processes by laser-indu...With the rapid advancement of laser decontamination technology and growing awareness of microbial hazards,it becomes crucial to employ theoretical model to simulate and evaluate decontamination processes by laser-induced plasma.This study employs a two-dimensional axisymmetric fluid dynamics model to simulate the power density of plasma bombardment on bacteria and access its decontamination effects.The model considers the transport processes of vapor plasma and background gas molecules.Based on the destructive impact of high-speed moving particles in the plasma on bacteria,we investigate the bombardment power density under various conditions,including different laser spot sizes,wavelengths,plate's tilt angles,and plate-target spacing.The results reveal that the bombardment power density increases with a decrease in laser spot size and wavelength.For instance,when the plate is parallel to the target surface with a 1 mm spacing,the bombardment power density triples as the laser spot size decreases from 0.8 mm to 0.5 mm and quadruples as the wavelength decreases from 1064 nm to 266 nm.Notably,when the plate is parallel to the target with a relatively close spacing of 0.5 mm,the bombardment power density at 0°inclination increases sevenfold compared to 45°.This simulation study is essential for optimizing optical parameters and designing component layouts in decontamination devices using laser-induced plasma.The reduction of laser spot size,wavelength,plate-target spacing and aligning the plate parallel to the target,collectively contribute to achieving precise and effective decontamination.展开更多
Chymosin is one of the critical enzymes in cheese making.Herein,we proposed a novel fluorometric assay for chymosin determination.Firstly,covalent organic frameworks(COF)were synthesized and exfoliated to 2-dimensiona...Chymosin is one of the critical enzymes in cheese making.Herein,we proposed a novel fluorometric assay for chymosin determination.Firstly,covalent organic frameworks(COF)were synthesized and exfoliated to 2-dimensional COF nanosheets(COF NS)by ultrasound treatment.Gold nanoparticles(Au NPs)were loaded with COF NS to prepare AuNPs/COF NS(Au@COF NS).Secondly,rhodamine B(RhB)modified substrate peptide(Pep)for chymosin was linked with Au@COF NS to construct a Pep-Au@COF NS nanocomposite.For the sensing principle,fluorescence of RhB was quenched by Au@COF NS and the fluorescence intensity was weak due to the fluorescence resonance energy transfer between COF NS and RhB of Pep.However,in the presence of chymosin,the RhB was released by specific cleavage of the substrate peptide by chymosin and resulted in the recovery of fluorescence.The increased fluorescence intensity was proportional to the increase of chymosin concentration and thus a“turn on”fluorescent sensor for chymosin was constructed.The sensor showed a linear range in the concentration of 0.05-60.00μg/mL for the detection of chymosin with a detection limit of 20 ng/mL.The sensor was used to quantify chymosin in rennet product with good selectivity,which has the potential applications in cheese manufacturing.展开更多
The matrix thermal properties have an important impact on laser-induced plasma,as the thermal effect dominates the interaction between ns-pulsed laser and matter,especially in metals.We used a series of pure metals an...The matrix thermal properties have an important impact on laser-induced plasma,as the thermal effect dominates the interaction between ns-pulsed laser and matter,especially in metals.We used a series of pure metals and aluminum alloys to measure plasma temperature and electron density through laser-induced breakdown spectroscopy,in order to investigate the effect of matrix thermal properties on laser-induced plasma.In pure metals,a significant negative linear correlation was observed between the matrix thermal storage coefficient and plasma temperature,while a weak correlation was observed with electron density.The results indicate that metals with low thermal conductivity or specific heat capacity require less laser energy for thermal diffusion or melting and evaporation,resulting in higher ablation rates and higher plasma temperatures.However,considering ionization energy,thermal effects may be a secondary factor affecting electron density.The experiment of aluminum alloy further confirms the influence of thermal conductivity on plasma temperature and its mechanism explanation.展开更多
文摘Laser-induced fluorescence(LIF)spectroscopy is employed for plasma diagnosis,necessitating the utilization of deconvolution algorithms to isolate the Doppler effect from the raw spectral signal.However,direct deconvolution becomes invalid in the presence of noise as it leads to infinite amplification of high-frequency noise components.To address this issue,we propose a deconvolution algorithm based on the maximum entropy principle.We validate the effectiveness of the proposed algorithm by utilizing simulated LIF spectra at various noise levels(signal-to-noise ratio,SNR=20–80 d B)and measured LIF spectra with Xe as the working fluid.In the typical measured spectrum(SNR=26.23 d B)experiment,compared with the Gaussian filter and the Richardson–Lucy(R-L)algorithm,the proposed algorithm demonstrates an increase in SNR of 1.39 d B and 4.66 d B,respectively,along with a reduction in the root-meansquare error(RMSE)of 35%and 64%,respectively.Additionally,there is a decrease in the spectral angle(SA)of 0.05 and 0.11,respectively.In the high-quality spectrum(SNR=43.96 d B)experiment,the results show that the running time of the proposed algorithm is reduced by about98%compared with the R-L iterative algorithm.Moreover,the maximum entropy algorithm avoids parameter optimization settings and is more suitable for automatic implementation.In conclusion,the proposed algorithm can accurately resolve Doppler spectrum details while effectively suppressing noise,thus highlighting its advantage in LIF spectral deconvolution applications.
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.51536002,61405048,and 91441130)。
文摘To measure the equivalent ratio distribution of the two-stage lean premixed(DLP)flame,we propose using acetone/toluene planar laser-induced fluorescence(PLIF)technology to simultaneously measure the concentrations of the two components.Appropriate excitation laser wavelength and filters are used to assess the influence of acetone and toluene on each other’s fluorescence signal at room temperature.Experimental results show that acetone has a strong absorption effect on toluene’s fluorescence signal,the effective absorption cross-section is 5.77×10-20 cm-2.Acetone has an obvious quenching effect on the toluene fluorescence signal,and the Stern–Volmer coefficient is 0.50 kPa-1.The collisions between the molecules of toluene and acetone will lead to the enhancement of the fluorescence signal of acetone,and the enhancement coefficient is exponential with the acetone’s concentration.The quantitative relationship between the fluorescence intensity and the concentrations of the two tracers is obtained by establishing the photophysical model of toluene and acetone’s fluorescence signals.
基金supported by National Natural Science Foundation of China(No.51777091)Innovative Talents Team Project of‘Six Talent Peaks’of Jiangsu Province(No.TDJNHB-006)Postgraduate Research&Practice Innovation Program of Jiangsu Province in China(No.SJCX20_0345)。
文摘In this paper the OH radicals produced by a needle-plate negative DC discharge in water vapor,N_(2)+H_(2)O mixture gas and He+H_(2)O mixture gas are investigated by a laser-induced fluorescence(LIF)system.With a ballast resistor in the circuit,the discharge current is limited and the discharges remain in glow.The OH rotation temperature is obtained from fluorescence rotational branch fitting,and is about 350 K in pure water vapor.The effects of the discharge current and gas pressure on the production and quenching processes of OH radicals are investigated.The results show that in water vapor and He+H_(2)O mixture gas the fluorescence intensity of OH stays nearly constant with increasing discharge current,and in N_(2)+H_(2)O mixture gas the fluorescence intensity of OH increases with increasing discharge current.In water vapor and N_(2)+H_(2)O mixture gas the fluorescence intensity of OH decreases with increasing gas pressure in the studied pressure range,and in He+H_(2)O mixture gas the fluorescence intensity of OH shows a maximum value within the studied gas pressure range.The physicochemical reactions between electrons,radicals,ground and metastable molecules are discussed.The results in this work contribute to the optimization of plasma reactivity and the establishment of a molecule reaction dynamics model.
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.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51976233 and 91641118).
文摘The effects of temperature and pressure on laser-induced fluorescence(LIF)of OH are numerically studied under the excitation of A-X(1,0)transition at high pressures.A detailed theoretical analysis is carried out to reveal the physical processes of LIF.It is shown that high pressure LIF measurements get greatly complicated by the variations of pressure-and temperature-dependent parameters,such as Boltzmann fraction,absorption lineshape broadening,central-frequency shifting,and collisional quenching.Operations at high pressures require a careful choice of an excitation line,and the Q1(8)line in the A-X(1,0)band of OH is selected due to its minimum temperature dependence through the calculation of Boltzmann fraction.The absorption spectra of OH become much broader as pressure increases,leading to a smaller overlap integral and thus smaller excitation efficiency.The central-frequency shifting cannot be omitted at high pressures,and should be taken into account when setting the excitation frequency.The fluorescence yield is estimated based on the LASKIN calculation.Finally,OH-LIF measurements were conducted on flat stoichiometric CH4/air flames at high pressures.And both the numerical and experimental results illustrate that the pressure dependence of fluorescence yield is dominated,and the fluorescence yield is approximately inversely proportional to pressure.These results illustrate the physical processes of OH-LIF and provide useful guidelines for high-pressure application of OH-LIF.
基金supported by National Natural Science Foundation of China(No.11805275)Hunan Provincial Natural Science Foundation of China(No.2018JJ3592)。
文摘Non-intrusive characterization of the singly ionized xenon velocity in Hall thruster plume using laser induced fluorescence(LIF)is critical for constructing a complete picture of plume plasma,deeply understanding the ion dynamics in the plume,and providing validation data for numerical simulation.This work presents LIF measurements of singly ionized xenon axial velocity on a grid ranging from 100 to 300 mm in axial direction and from 0 to 50 mm in radial direction for a600 W Hall thruster operating at the nominal condition of discharge voltage 300 V and discharge current 2 A,the influence of discharge voltage is investigated as well.The ion velocity distribution function(IVDF)results in the far-field plume demonstrate a profile of bimodal IVDFs,especially prominent at radial distances greater than channel inner radius of 22 mm at axial position of 100 mm,which is quite different from that of the near-field plume where bimodal IVDFs occur in the central core region for the same power Hall thruster when compared to previous LIF measurements of BHT-600 by Hargus(2010 J.Propulsion Power 26135).Beyond 100 mm,only single-peak IVDFs are measured.The two-dimensional ion velocity vector field indicates the bimodal axial IVDF is merely a geometry effect for the annular discharge channel in the far-field plume.Results about the IVDF,the most probable velocity and the accelerating potential profile along the centerline all indicate that ions are still accelerating at axial distances greater than 100 mm,and the maximum most probable velocity measured at300 mm downstream of the exit plane is about 19 km s-1.In addition,the most probable velocity of ions along radial direction changes a little except the lower velocity ion populations in the bimodal IVDF cases.The ion temperature at axial distances of 10 and 300 mm oscillates along the radial direction,while the ion temperature first increases,and then decreases for the 200 mm case.Finally,the axial position for the ion peak axial velocity on the thruster centerline is shifted upstream for higher discharge voltages,and the velocity curve is becoming steeper with the discharge voltage before reaching the maximum.This observation can be used as a criterion to optimize the thruster performance.
基金Project supported by the National Natural Science Foundation of China(Grant No.21903050)。
文摘As a model molecule of actinide chemistry,UO molecule plays an important role in understanding the electronic structure and chemical bonding of actinide-containing species.We report a study of the laser-induced fluorescence spectra of the U^(16)O and U^(18)O using two-dimensional spectroscopy.Several rotationally resolved excitation spectra were investigated.Accurate molecular rotational constants and equilibrium internuclear distances were reported.Low-lying electronic states information was extracted from high resolution dispersed fluorescence spectra and analyzed by the ligand field theory model.The configuration of the ground state was determined as U^(2+)(5 f^(3)7 s)O^(2-).The branching ratios,and the vibrational harmonic and anharmonic parameters were also obtained.Radiative lifetimes were determined by recording the timeresolved fluorescence spectroscopy.Transition dipole moments were calculated using the branching ratios and the radiative lifetimes.These findings were elucidated by using quantum-chemical calculations,and the chemical bonding was also analyzed.The findings presented in this work will enrich our understanding of actinide-containing molecules.
基金financially supported by National Natural Science Foundation of China(No.62005078)the Scientific Research Foundation of Hunan Provincial Education Department(No.21B0477)the Natural Science Foundation of Hunan Province(No.2020JJ5206)。
文摘The detection of manganese(Mn)in steel by laser-induced breakdown spectroscopy(LIBS)provides essential information for steelmaking.However,self-absorption greatly disrupts the LIBS spectral lines of Mn with high content.In this study,to minimize self-absorption for Mn spectral lines in LIBS,laser-induced fluorescence(LIF)was applied.Compared with conventional LIBS,the self-absorption factors(α)of Mn I 403.08,403.31,and 403.45 nm lines were reduced by 90%,88%,and 88%,respectively;the root mean square errors of crossvalidation were decreased by 88%,85%,and 87%,respectively;the average relative errors were reduced by 93%,90%,and 91%,respectively;and average relative standard deviations were decreased by 29%,32%,and 33%,respectively.The LIBS-LIF was shown to successfully minimize the self-absorption effect and spectral intensity fluctuation and improve detection accuracy.
文摘Bay-site carboxyl functionalized perylene diimide derivative 1,7-COOH-PDI-C_(12)(PDI-COOH)was synthesized and distinct enhanced fluorescence was observed through combining with calcium ion(Ca^(2+))in THF/H_(2)O solution.The assembly and fluorescence behavior of PDI-COOH/Ca^(2+)were studied in detail by changing hydration state with different concentrations.Based on the differences in assembly morphology and stoichiometric ratios of PDICOOH/Ca^(2+),we proposed the fluorescence emission mechanism of PDI-COOH/Ca^(2+)in THF/H_(2)O and THF,respectively.This work reveals a novel strategy of aggregated state fluorescence enhancement and reminds us of the important role of water in molecular fluorescence emission and assembly.
基金supported by National Energy R&D Center of Petroleum Refining Technology of China(RIPP,SINOPEC)National Key Research and Development Program of China(No.2017YFA0304203)+5 种基金Changjiang Scholars and Innovative Research Team in University of Ministry of Education of China(No.IRT_17R70)National Natural Science Foundation of China(Nos.61975103,61875108,61775125 and 11434007)Industrial Application Innovation Project(No.627010407)Scientific and Technological Innovation Project of Shanxi Gemeng US-China Clean Energy R&D Center Co.,Ltd111 Project(D18001)Fund for Shanxi‘1331KSC’。
文摘Although laser-induced breakdown spectroscopy(LIBS),as a fast on-line analysis technology,has great potential and competitiveness in the analysis of chemical composition and proximate analysis results of coal in thermal power plants,the measurement repeatability of LIBS needs to be further improved due to the difficulty in controlling the stability of the generated plasmas at present.In this paper,we propose a novel x-ray fluorescence(XRF) assisted LIBS method for high repeatability analysis of coal quality,which not only inherits the ability of LIBS to directly analyze organic elements such as C and H in coal,but also uses XRF to make up for the lack of stability of LIBS in determining other inorganic ash-forming elements.With the combination of elemental lines in LIBS and XRF spectra,the principal component analysis and the partial least squares are used to establish the prediction model and perform multi-elemental and proximate analysis of coal.Quantitative analysis results show that the relative standard deviation(RSD) of C is 0.15%,the RSDs of other elements are less than 4%,and the standard deviations of calorific value,ash content,sulfur content and volatile matter are 0.11 MJ kg,0.17%,0.79% and 0.41%respectively,indicating that the method has good repeatability in determination of coal quality.This work is helpful to accelerate the development of LIBS in the field of rapid measurement of coal entering the power plant and on-line monitoring of coal entering the furnace.
基金Supported by the National Natural Science Foundation of China under Grant No.19875083.
文摘By means of one photon absorption laser-induced resonance fluorescence at 599.5 nm the relative concentrations of amidogen(NH_(2))radical in the ammonia(NH_(3))radio-frequency(rf)plasma source were measured under different discharge pressures and rf powers.The time dependence of the fluorescence which comes from the radiation 101-211 of the P-branches of the Σ vibronic sub-bands can be described by a single-exponential decay.The decay time of NH_(2)(A2A1)Σ(0,9,0)rovibronic state was determined.The spatial dependence of the NH_(2) density in discharge tube was measured.
基金supports from the National Natural Science Foundation of China(12074123,12174108)the Foundation of‘Manufacturing beyond limits’of Shanghai‘Talent Program'of Henan Academy of Sciences.
文摘Femtosecond laser-induced periodic surface structures(LIPSS)have been extensively studied over the past few decades.In particular,the period and groove width of high-spatial-frequency LIPSS(HSFL)is much smaller than the diffraction limit,making it a useful method for efficient nanomanufacturing.However,compared with the low-spatial-frequency LIPSS(LSFL),the structure size of the HSFL is smaller,and it is more easily submerged.Therefore,the formation mechanism of HSFL is complex and has always been a research hotspot in this field.In this study,regular LSFL with a period of 760 nm was fabricated in advance on a silicon surface with two-beam interference using an 800 nm,50 fs femtosecond laser.The ultrafast dynamics of HSFL formation on the silicon surface of prefabricated LSFL under single femtosecond laser pulse irradiation were observed and analyzed for the first time using collinear pump-probe imaging method.In general,the evolution of the surface structure undergoes five sequential stages:the LSFL begins to split,becomes uniform HSFL,degenerates into an irregular LSFL,undergoes secondary splitting into a weakly uniform HSFL,and evolves into an irregular LSFL or is submerged.The results indicate that the local enhancement of the submerged nanocavity,or the nanoplasma,in the prefabricated LSFL ridge led to the splitting of the LSFL,and the thermodynamic effect drove the homogenization of the splitting LSFL,which evolved into HSFL.
基金financial supports from National Natural Science Foundation of China(No.62205172)Huaneng Group Science and Technology Research Project(No.HNKJ22-H105)Tsinghua University Initiative Scientific Research Program and the International Joint Mission on Climate Change and Carbon Neutrality。
文摘Laser-induced breakdown spectroscopy(LIBS)has become a widely used atomic spectroscopic technique for rapid coal analysis.However,the vast amount of spectral information in LIBS contains signal uncertainty,which can affect its quantification performance.In this work,we propose a hybrid variable selection method to improve the performance of LIBS quantification.Important variables are first identified using Pearson's correlation coefficient,mutual information,least absolute shrinkage and selection operator(LASSO)and random forest,and then filtered and combined with empirical variables related to fingerprint elements of coal ash content.Subsequently,these variables are fed into a partial least squares regression(PLSR).Additionally,in some models,certain variables unrelated to ash content are removed manually to study the impact of variable deselection on model performance.The proposed hybrid strategy was tested on three LIBS datasets for quantitative analysis of coal ash content and compared with the corresponding data-driven baseline method.It is significantly better than the variable selection only method based on empirical knowledge and in most cases outperforms the baseline method.The results showed that on all three datasets the hybrid strategy for variable selection combining empirical knowledge and data-driven algorithms achieved the lowest root mean square error of prediction(RMSEP)values of 1.605,3.478 and 1.647,respectively,which were significantly lower than those obtained from multiple linear regression using only 12 empirical variables,which are 1.959,3.718 and 2.181,respectively.The LASSO-PLSR model with empirical support and 20 selected variables exhibited a significantly improved performance after variable deselection,with RMSEP values dropping from 1.635,3.962 and 1.647 to 1.483,3.086 and 1.567,respectively.Such results demonstrate that using empirical knowledge as a support for datadriven variable selection can be a viable approach to improve the accuracy and reliability of LIBS quantification.
基金Project supported by the National Key Research and Development Program of China(Grant No.2017YFA0402300)the National Natural Science Foundation of China(Grant Nos.U2241288 and 11974359).
文摘Taking three typical soft samples prepared respectively by loose packings of 77-,95-,and 109-μm copper grains as examples,we perform an experiment to investigate the energy-dependent laser-induced breakdown spectroscopy(LIBS)of soft materials.We discovered a reversal phenomenon in the trend of energy dependence of plasma emission intensity:increasing initially and then decreasing separated by a well-defined critical energy.The trend reversal is attributed to the laser-induced recoil pressure at the critical energy just matching the sample's yield strength.As a result,a one-to-one correspondence can be well established between the samples'yield stress and the critical energy that is easily obtainable from LIBS measurements.This allows us to propose an innovative method for estimating the yield stress of soft materials via LIBS with attractive advantages including in-situ remote detection,real-time data collection,and minimal destructive to sample.
基金supported by National Key R&D Program of China(No.2017YFA0304203)National Energy R&D Center of Petroleum Refining Technology(RIPP,SINOPEC),Changjiang Scholars and Innovative Research Team in University of Ministry of Education of China(No.IRT_17R70)+2 种基金National Natural Science Foundation of China(Nos.12374377,61975103 and 627010407)111 Project(No.D18001)Fund for Shanxi‘1331KSC’。
文摘With the rapid advancement of laser decontamination technology and growing awareness of microbial hazards,it becomes crucial to employ theoretical model to simulate and evaluate decontamination processes by laser-induced plasma.This study employs a two-dimensional axisymmetric fluid dynamics model to simulate the power density of plasma bombardment on bacteria and access its decontamination effects.The model considers the transport processes of vapor plasma and background gas molecules.Based on the destructive impact of high-speed moving particles in the plasma on bacteria,we investigate the bombardment power density under various conditions,including different laser spot sizes,wavelengths,plate's tilt angles,and plate-target spacing.The results reveal that the bombardment power density increases with a decrease in laser spot size and wavelength.For instance,when the plate is parallel to the target surface with a 1 mm spacing,the bombardment power density triples as the laser spot size decreases from 0.8 mm to 0.5 mm and quadruples as the wavelength decreases from 1064 nm to 266 nm.Notably,when the plate is parallel to the target with a relatively close spacing of 0.5 mm,the bombardment power density at 0°inclination increases sevenfold compared to 45°.This simulation study is essential for optimizing optical parameters and designing component layouts in decontamination devices using laser-induced plasma.The reduction of laser spot size,wavelength,plate-target spacing and aligning the plate parallel to the target,collectively contribute to achieving precise and effective decontamination.
基金supported by Major Science and Technology Project of Yunnan Province(202302AE090022)Key Research and Development Program of Yunnan(202203AC100010)+4 种基金the National Natural Science Foundation of China(32160597,32160236,32371463)National Key Research and Development Program of China(2022YFC2601604)Cardiovascular Ultrasound Innovation Team of Yunnan Province(202305AS350021)Spring City Plan:the High-Level Talent Promotion and Training Project of Kunming(2022SCP001)Graduate Tutor Team of Yunnan Province,and the Second Phase of"Double-First Class"Program Construction of Yunnan University.
文摘Chymosin is one of the critical enzymes in cheese making.Herein,we proposed a novel fluorometric assay for chymosin determination.Firstly,covalent organic frameworks(COF)were synthesized and exfoliated to 2-dimensional COF nanosheets(COF NS)by ultrasound treatment.Gold nanoparticles(Au NPs)were loaded with COF NS to prepare AuNPs/COF NS(Au@COF NS).Secondly,rhodamine B(RhB)modified substrate peptide(Pep)for chymosin was linked with Au@COF NS to construct a Pep-Au@COF NS nanocomposite.For the sensing principle,fluorescence of RhB was quenched by Au@COF NS and the fluorescence intensity was weak due to the fluorescence resonance energy transfer between COF NS and RhB of Pep.However,in the presence of chymosin,the RhB was released by specific cleavage of the substrate peptide by chymosin and resulted in the recovery of fluorescence.The increased fluorescence intensity was proportional to the increase of chymosin concentration and thus a“turn on”fluorescent sensor for chymosin was constructed.The sensor showed a linear range in the concentration of 0.05-60.00μg/mL for the detection of chymosin with a detection limit of 20 ng/mL.The sensor was used to quantify chymosin in rennet product with good selectivity,which has the potential applications in cheese manufacturing.
基金supported by the National Key Research and Development Project(Grant No.2018YFC2001100).
文摘The matrix thermal properties have an important impact on laser-induced plasma,as the thermal effect dominates the interaction between ns-pulsed laser and matter,especially in metals.We used a series of pure metals and aluminum alloys to measure plasma temperature and electron density through laser-induced breakdown spectroscopy,in order to investigate the effect of matrix thermal properties on laser-induced plasma.In pure metals,a significant negative linear correlation was observed between the matrix thermal storage coefficient and plasma temperature,while a weak correlation was observed with electron density.The results indicate that metals with low thermal conductivity or specific heat capacity require less laser energy for thermal diffusion or melting and evaporation,resulting in higher ablation rates and higher plasma temperatures.However,considering ionization energy,thermal effects may be a secondary factor affecting electron density.The experiment of aluminum alloy further confirms the influence of thermal conductivity on plasma temperature and its mechanism explanation.
