Research on a deconvolution algorithm for laser-induced fluorescence diagnosis based on the maximum entropy principle

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.

Quantitative measurement of hydroxyl radical(OH) concentration in premixed flat flame by combining laser-induced fluorescence and direct absorption spectroscopy

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.

Quantitative measurements of one-dimensional OH absolute concentration profiles in a methane/air flat flame by bi-directional laser-induced fluorescence

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.

Elemental and proximate analysis of coal by x-ray fluorescence assisted laser-induced breakdown spectroscopy

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.

Absorption,quenching,and enhancement by tracer in acetone/toluene laser-induced fluorescence

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.

Numerical analysis of quantitative measurement of hydroxyl radical concentration using laser-induced fluorescence in flame

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.

The investigation of OH radicals produced in a DC glow discharge by laser-induced fluorescence spectrometry

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.

Simultaneous laser-induced fluorescence and contactless-conductivity detection for microfluidic chip

A combined detection system involving simultaneous LIF and contacfless-conductometric measurements at the same place of the microfluidic chip was described. The LIF measurement was designed according to the confocal principle and a moveable contactless-conduetivity detector was used in C^4D. Both measurements were mutually independent and advantageous in analyses of mixtures. Various experimental parameters affecting the response were examined and optimized. The performances were demonstrated by simultaneous detection of Rhodamine B. And the results showed that the combined detection system could be used sensitively and reliably.

Absolute density measurement of nitrogen dioxide with cavity-enhanced laser-induced fluorescence

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.

Effects of temperature and pressure on OH laser-induced fluorescence exciting A-X (1,0) transition at high pressures

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.

Laser-induced fluorescence experimental spectroscopy and theoretical calculations of uranium monoxide

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.

Determination of Amino Acids in an Individual Erythrocyteby Capillary Electrophoresis with Intracellular FITC-derivatization and Laser-induced Fluorescence Detection

A novel approach for analysis of amino acids in individual erythrocytes was established. In this method, the derivatization reagent was introduced into the living cells by electroporation. After derivatization, the amino acids in a single cell were determined by capillary electrophoresis with laser-induced fluorescence detection.

The far-field plasma characterization in a 600W Hall thruster plume by laser-induced fluorescence

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.

Mixed Micellar Electrokinetic Chromatographic Analysis of Colistin, Polypeptide Antibiotic, Using Laser-Induced Fluorescence Detection

The main goal of this work was to quantify the detection of colistin at low levels in urine samples through the practical application of mixed surfactant micellar electrokinetic chromatography–laser-induced fluorescence (MEKC-LIF) analysis method using its advantage of sensitivity and to examine direct injection of biological samples. Colistin (po- lymyxin E) has neither strong UV chromophore nor fluorophore. So, its assay for metabolism, pharmacokinetics studies for bioavailability and bioequivalence are difficult because of poor detectability. Therefore an enhanced UV or fluores-cence detection by chemical derivatization is required. MEKC-LIF method was proposed for colistin with a 488/520 nm argon-ion laser using a pre-CE derivatization with fluorescein isothiocyanate (FITC). Borate buffer was used as background buffer (BGB). The different parameters affecting the proposed derivatization reaction including concentration of the derivatizing reagent, reaction time and temperature were studied and optimized. The derivative was stable for up to 3 days. Different micelles (TX-100 and SDS) were examined as BGB additives separately but negative-charged mixed micelles (SDS/TX-100) were shown to be the best additive to BGB for the analysis of colistin particularly in human urine as they enhance both selectivity and sensitivity of the proposed method. BGB was used with pH 9.5, 10 kV, 8 s inj time, capillary length 75 cm × 75 μm ID (66 cm effective length), detection was LIF Ex 488 nm;Em 520 nm. The method was applied to colistin analysis in human urine and the recovery was > 98% (n = 5). LOD and LOQ in urine after pre-column derivatization using FITC were 100 and 250 ng/ml, respectively. Urine samples were analysed by direct injection without sample pre-treatment. The mechanism of enhancement of fluorescence of the derivative by surfactant was proposed.

Effect of gas components on the postdischarge temporal behavior of OH and O of a non-equilibrium atmospheric pressure plasma driven by nanosecond voltage pulses

OH radicals and O atoms are two of the most important reactive species of non-equilibrium atmospheric pressure plasma(NAPP),which plays an important role in applications such as plasma medicine.However,experimental studies on how the gas content affects the postdischarge temporal evolutions of OH and O in the noble gas ns-NAPP are very limited.In this work,the effect of the percentages of O_(2),N_(2),and H_(2)O on the amounts of OH and O productions and their post-discharge temporal behaviors in ns-NAPP is investigated by laser-induced fluorescence(LIF)method.The results show that the productions of OH and O increase and then decrease with the increase of O_(2)percentage.Both OH and O densities reach their maximum when about 0.8%O_(2)is added.Further increase of the O_(2)concentration results in a decrease of the initial densities of both OH and O,and leads to their faster decay.The increase of N_(2)percentage also results in the increase and then decrease of the OH and O densities,but the change is smaller.Furthermore,when the H_(2)O concentration is increased from 100 to 3000 ppm,the initial OH density increases slightly,but the OH density decays much faster,while the initial density of O decreases with the increase of the H_(2)O concentration.After analysis,it is found that OH and O are mainly produced through electron collisional dissociation.O(^(1)D)is critical for OH generation.O_(3)accelerates the consumption processes of OH and O at high O_(2)percentage.The addition of H_(2)O in the NAPP considerably enhances the electronegativity,while it decreases the overall plasma reactivity,accelerates the decay of OH,and reduces the O atom density.

Laser-induced fluorescence of macerals in relation to its hydrogen richness

On the basis of results from conventional elemental analyses and a unique technique (FAMM? fluorescence alteration of multiple macerals), using a laser fluorescence microprobe, the fluorescence characteristics of various macerals are systematically related to hydrogen content. The amount of fluorescence from inertinite and vitrinite exponentially increases with H/C values. Although liptinite has high fluorescence and high H/C values, the relationship does not follow the same trend as defined for the other maceral groups. Because petroleum yields of a maceral mainly depend upon hydrogen richness, a correlation also exists between fluorescence, and gas to oil ratios from pyrolysis. Because individual organic entities are measured, the laser fluorescence microprobe has the benefit of accommodating heterogeneous organic matter in source rocks and enables determination of oil and gas yields of specific macerals.

Observation of hydrocarbon generation and migration of highly-matured carbonates by means of laser-induced fluorescence microscopy

Some important information on hydrocarbon generation, inclusion and migration inhighly-matured carbonates of lower Palaeozoic age from the Ordos Basin and Tarim Basin has been analyzed by a newly-combined laser-induced fluorescence microscope (LFM) designed by our laboratory. The following information has been obtained from the lower Ordovician lamellar carbonates with equivalent vitrinite reflectance (Ro) as high as 1.6%-1.7% and residual TOC of 0.14%-0.35% from the Ordos Basin: wide occurrences of oil and source macerals with strong fluorescence, including G.Prisca alginite, lamalginite, telalginite and algae-detrinite; fluorescing asphalt among mineral crystals; some groundmass and spheroid-like reservoir bitumen with high maturation levels in the pores of dolomites. Various kinds of fluorescing organic inclusions and asphalt have been found in the carbonates, calcareous shales and silt-shales with high maturation levels from the Cambrian-Ordovician strata in the Tarim Basin. All this helps us find

Periphery excitation of laser-induced CN fluorescence in plasma using laser-induced breakdown spectroscopy for carbon detection

Carbon is hard to be sensitively detected in laser-induced breakdown spectroscopy(LIBS).The optical emission can be significantly enhanced by resonantly exciting CN radicals in the plasma center using LIBS assisted with laser-induced fluorescence(LIBS-LIF).However,the nitrogen source for CN formation is provided by ambient gas.Therefore,we propose a new approach of periphery excitation in plasma to improve CN fluorescence.The optical and spatial characteristics of CN radicals in plasma were discussed.A fluorescence map was established by combining focal point location and fluorescent intensity,demonstrating that plasma periphery had 4.2 times stronger fluorescence than the center.

Theoretical study of determining orientation and alignment of symmetric top molecule using laser-induced fluorescence

General expressions used for extracting the orientation and alignment parameters of a symmetric top molecule from laser-induced fluorescence (LIF) intensity are derived by employing the density matrix approach. The molecular orientation and alignment are described by molecular state multipoles. Excitation and detection are circularly and linearly polarized lights, respectively. In general cases, the LIF intensity is a complex function of the initial molecular state multipoles, the dynamic factors and the excitation-detection geometrical factors. It contains a population, ten orientation and fourteen alignment multipoles. The problem of how to extract the initial molecular state multipoles from the resolved LIF intensity is discussed.