Laser induced fluorescence diagnostic for velocity distribution functions:applications,physics,methods and developments

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.

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.

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.

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.

Ion Transport Measurements in a Multi-Dipole Argon Plasma by Broadband Laser Induced Fluorescence

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.

Detection of Petroleum Pollutants by Using Laser Induced Fluorescence Imaging

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.

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.

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.

Hyperspectral imaging and remote trace detection of cis-1,3,4,6-tetranitrooctahydroimidazo-[4,5 d]imidazole(BCHMX)compared with traditional explosives using laser induced fluorescence

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).

Laser Induced Fluorescence Spectroscopy of IrN

High resolution laser induced fluorescence, spectra of IrN in the spectral region between 394 and 520 nm were recorded using laser vaporization/reaction free jet expansion and laser induced fluorescence spectroscopy. Seven new vibronic transition bands were observed and analyzed. Two Ω=1 and five Ω=0 new states were identified. Least squares fit of rotationally resolved transition lines yielded accurate molecular constants for the upper states. Spectra of isotopic molecules were observed, which provided confirmation for the vibrational assignment. Comparison of the observed electronic states of IrB, IrC, and IrN provides a good understanding of the chemical bonding of this group of molecules.

Research of Confocal Laser Induced Fluorescence Detection System for Micro-fluidic Chip

The characteristics such as signal noise ratio（SNR） and sensitivity of the fluorescence detection system for micro-fluidic chip influence the performance of the whole system extremely. The confocal laser induced fluorescence detection system is presented. Based on the debugging of optical and circuit modules, the results of detecting the samples are given and analyzed theoretically, and the improved project is put forward.

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.

Production of Polyclonal Antibody of Morphine and Determination of Morphine in Urine by Capillary Electrophoresis Immunoassay with Laser-induced Fluorescence Detection

N-Conjugated antigen was synthesized and polyclonal antibody with high specificity was obtained from immunizing animals. With this polyclonal antibody, a rapid and efficient CEIA-LIF method was developed to determine the free morphine in urine of abusers. The detection limit was calculated to be 40 ng/mL. Simulated urine samples were analyzed with good recoveries, which showed the feasibility of its application in specific morphine determination in urine of morphine abusers.

Advantage of Introducing Quantitative Light-Induced Fluorescence in School Dental Checkups

Background: Caries detection in school oral examinations insufficient accuracy. Objective: To evaluate advantages of introducing quantitative light-induced fluorescence-digital (QLF-D) in school oral examinations. Methods: Experiment No. 1. Early demineralized lesions in the upper and lower incisors and canines were visually inspected by three dentists and by QLF-D. The numbers of tooth planes with early demineralized lesions were compared between the methods. Experiment No. 2. Approximal demineralized lesions in molars were assessed by visual inspection, x-ray imaging, and QLF-D. The numbers of tooth planes with demineralized lesions were compared among the methods. Experiment No. 3. Plaque distribution was evaluated by QLF-D and a traditional staining method. The ratio of the diameter of plaque to tooth crown in the tooth axis direction in each method was calculated. The results were evaluated by Pearson’s correlation coefficient analysis and Bland-Altman plot. Results: Experiment No. 1. The three dentists found 0.67 tooth planes on average. QLF-D found 22 tooth planes with early demineralized lesions in the same samples. Experiment No. 2. Fourteen approximal tooth planes of molars were found to have demineralized lesions by x-ray imaging. QLF-D detected 71.4% of the tooth planes out of the 14, whereas visual inspection found 7.1%. Experiment No. 3. The Pearson’s correlation coefficient for the evaluations of plaque distribution between the QLF-D and traditional staining methods was 0.77 (P Conclusion: The results support introduction of QLF-D for use in school dental examinations.

Evaluating Acid Resistance Effect of Fluoride-Releasing Dental Materials Using Quantitative Light-Induced Fluorescence-Digital in Vitro

As erosion has become one of the serious oral health problems, some fluoride-releasing dental materials have been developed to protect enamel from demineralization. The purpose of this study was to evaluate the antidemineralization effect of PRG Barrier Coat® and FujiVII® (fluoride-releasing dental materials). Four square windows measuring 1 mm2 were prepared on the labial enamel surface of each bovine tooth using masking tape and nail varnish. The first and second windows were half covered by fluoride-releasing material and control material, respectively, whereas the third and fourth windows were left untreated. All windows were immersed into 0.1 M lactic acid and 6wt% CM-cellulose (pH 4.5) at 38℃ for 21 days. Subsequently, the first and second windows were covered with nail varnish after removal of the materials, and the third and fourth windows were immersed into ultrapure water at 38℃ for 28 days after being half covered with fluoride-releasing and control materials, respectively. The following procedure was performed separately during evaluations of the fluoride-releasing materials, PRG Barrier Coat, and FujiVII®, using eight and six bovine teeth, respectively. The first, second, third, and fourth windows were classified into DM-PRG;Demineralized-PRG or DM-FujiVII;Demineralized-FujiVII, DM-TCM;Demineralized-traditional cement or DM-TGIC;De-mineralized-traditional glass ionomer cement, RM-PRG;Remineralized-PRG or RM-FujiVII;Re-mineralized-FujiVII, and RM-TCM;Remineralized- traditional cement or RM-TGIC;Remineral-ized-traditional glass ionomer cement, respectively. After nail varnish was removed, △Q values (mean ± SD) of the windows were measured using QLF-D and were compared between DM-PRG and DM-TCM, RM-PRG and RM-TCM, DM-FujiVII and DM-TGIC, and RM-FujiVII and RM-TGIC groups. △Q values of RM-PRG (-60 ± 44) and RM-FujiVII (-5.0 ± 10) were significantly higher than that of RM-TCM (-315 ± 193) and RM-TGIC (-56 ± 43), respectively. The fluoride releasing materials provided remineralization effects to bovine enamel.

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.

Radiation-induced attenuation self-compensating effect in super-fluorescent fiber source

The compact super-fluorescent fiber source （SFS） output spectra variations at different pump currents and under different dose of gamma-ray radiation were measured and compared respectively. The radiation-induced attenuation （RIA） self-compensating effect in SFS based on photo-bleaching was found and the general mathematic model of SFS output spectra variations was made. The radiation-induced background attenuation （RIBA） at the pump wavelength was identified to be the main cause of the total output power and spectra variations and the variations can then be compensated by active control of the pump power to enhance the self-compensating effect. With closed-loop feedback control of pump current, double-pass backward （DPB） configuration and spectrum re-shaping technology, an SFS prototype was made and tested. The mean-wavelength stability of about 87.4 ppm and output power instability of less than 5% were achieved under up to 200 krad （Si） gamma-ray irradiation.

Human induced pluripotent stem cells labeled with fluorescent magnetic nanoparticles for targeted imaging and hyperthermia therapy for gastric cancer

Objective: Human induced pluripotent stem(i PS) cells exhibit great potential for generating functional human cells for medical therapies. In this paper, we report for use of human i PS cells labeled with fluorescent magnetic nanoparticles(FMNPs) for targeted imaging and synergistic therapy of gastric cancer cells in vivo. Methods: Human i PS cells were prepared and cultured for 72 h. The culture medium was collected, and then was coincubated with MGC803 cells. Cell viability was analyzed by the MTT method. FMNP-labeled human i PS cells were prepared and injected into gastric cancer-bearing nude mice. The mouse model was observed using a small-animal imaging system. The nude mice were irradiated under an external alternating magnetic field and evaluated using an infrared thermal mapping instrument. Tumor sizes were measured weekly. Results: iP S cells and the collected culture medium inhibited the growth of MGC803 cells. FMNP-labeled human iP S cells targeted and imaged gastric cancer cells in vivo, as well as inhibited cancer growth in vivo through the external magnetic field. Conclusion: FMNP-labeled human i PS cells exhibit considerable potential in applications such as targeted dual-mode imaging and synergistic therapy for early gastric cancer.

Triplet Exciton Transition Induced Highly Efficient Fluorescent Channel in Organic Electroluminescence

The in.jection of charge carriers from the electron/hole injection or transport layers in polymer light-emitting diodes potentially increases the device efficiency not by changing of charge intensity but by lattice distortion variation and quasi-particle interactions. From the low-dimensional condensed matter physics perspective, a valid mechanism is proposed to bring a type of novel channels that, under a proper external electric field, transition- forbidden triplet excitons are transformed and partially charged by charge carriers （polarons/bipolarons）, thus are able to emit light and to enhance fluorescence greatly.

A ggregation-induced emission nanoparticles for in vivo three-photon fuorescence microscopic rat brain angiography

Rodents are popular biological models for physiological and behavioral research in neuroscience and rats are better models than mice due to their higher genome similarity to human and more accessible surgical procedures.However,rat brain is larger than mice brain and it needs powerful imaging tools to implement better penetration against the scattering of the thicker brain tissue.Three-photon fluorescence microscopy(3PFM)combined with near-infrared(NIR)excitation has great potentials for brain circuits imaging beause of its abilities of anti scattering,deep-tissue imaging,and high signal-to-noise ratio(SNR).In this work,a type of AIE lumninogen with red fuorescence was synthesized and encapsulated with Pluronic F-127 to make up form nano-particles(NPs).Bright DCDPP-2TPA NPs were employed for in trino three-photon fuorescent laser scanning microscopy of blood vessels in rats brain under 1550 nm femtosecond laser exci-tation.A fine three-dimensional(3D)reconstruction up to the deepness of 600 pm was achieved and the blood flow velocity of a selected vessel was measured in vrito as well.Our 3PFM deep brain imaging method simultaneously recorded the morphology and function of the brain blood vessels in vivo in the rat model.Using this angiography combined with the arsenal of rodent's brain disease,models can accelerate the neuroscience research and clinical diagnosis of brain disease in the future.