Laser-induced Fluorescence Spectra Research Articles

Laser-induced fluorescence spectroscopic investigation of Echium amoenum decoction

Herbs containing medicinal ingredients with nutritional value have recently gained attention as an alternative to synthetic drugs. Aside from their pharmaceutical worthiness, a variety of naturally occurring chromophores with specific optical properties have made them valuable sources of natural pigments for many biophotonic applications. Echium Amoenum (EA) is one of the colorful flowers that has been used in traditional medicine for a long time. To our knowledge, although several studies have been carried out on the characterization of EA ingredients and their chemical activities, information on EA fluorescence is still lacking. Here, laser induced fluorescence (LIF) features of the decoction of EA petals were evaluated and found to be highly dependent on the excitation wavelength, EA concentration, and detection geometry. The abundance of pigments, the boundaries of their absorption/emission spectral regions, and the corresponding energy transfer ascertain the contribution of certain chromophores to the cumulative fluorescence activity. Upon deconvolution of the LIF spectra, it was revealed that the different emission bands of rosmarinic acid (corresponding to its dissociated forms) and the luminescent activity of luteolin and β-carotene mainly determine the quantum distribution of the fluorescence of EA. Angular measurement of LIF in a symmetric cylindrical arrangement revealed the presence of the inner filters mainly due to the reabsorption of LIF photons by anthocyanins (flavone, pelargonidin, delphinidin and cyanidin) and carotenoids. We hope that the obtained results will be useful in various fields of photochemistry and biophotonics.

Laser induced fluorescence spectroscopy of the transition of jet cooled 14NO3 and 15NO3 II: the dispersed fluorescence spectrum from the 3rd E level of the ν4 mode (approximately the 2ν4 (e'), l = 0, level).

14NO3 and 15NO3 isotopomers were generated in a supersonic free jet expansion, and laser induced fluorescence (LIF) of the electronic transition was observed. Dispersed LIF spectra from the vibronic level at ∼770 cm-1 above the vibrationless level have been measured for each isotopomer. One remarkable characteristic of the dispersed fluorescence (DF) spectrum is that the ν2 fundamental is clearly observed, even though the transition 201 is forbidden in the electronic transition. Another is that two sets of vibrational structure are observed in the DF spectrum: one of the two sets is the structure with the origin at the excitation energy, and the other is that with the origin at the ν2 fundamental. These observations suggest that the fluorescent level has contribution from the ν2 mode. In part I (M. Fukushima, J. Mol. Spectrosc., 2022, 387, 111646), it has been reported that the ν4 progressions are one of the typical characteristics of the vibrational structure of the DF spectrum from the vibrationless level; the progressions have intensity gradually decreasing with increasing ν4 quantum number (named the "regular" distribution), and have members forbidden for the Δl = 0 selection rule. The intensity distribution of the ν4 progression with the origin at the ν2 fundamental is similar to that from the vibrationless level, while that with the origin at the excitation energy is drastically different from that from the vibrationless level. The Jahn-Teller (J-T) and Renner-Teller (R-T) interactions in the B̃2E' state enable us to interpret the intensity distributions of the ν4 progressions, in which relatively weak interactions are enough to reproduce the observed distributions. The spectral intensity distribution analyses adopting the two vibronic couplings suggest that the fluorescent level at ∼770 cm-1 above the vibrationless level is the 3rd E eigenstate of the ν4 mode. The major component of the ν4 3rd E state is the |Λ = ±1; v4 = 2, l4 = 0〉 level of the B̃2E' state, which is a vibrationally and a vibronically E' level, and it is therefore concluded that the major components of the fluorescent level are both of the ν2 = 1 level and ν4 = 2 level .

266 nm Laser-Induced Fluorescence Reference Spectra of Ketones and Aromatic Compounds

ABSTRACT Laser-induced fluorescence (LIF) is an established noninvasive measurement method to determine temperature distributions and local gas concentrations in combustion processes with high spatial and temporal resolution. This work presents high-precision LIF spectra of acetone and other tracers at ambient conditions. By using a large UV-sensitive sCMOS camera instead of an image intensified camera, many issues like nonlinearity, varying sensitivity, vignetting, limited resolution etc. could be minimized or eliminated. Particular care was taken to remove residual stray light and to calibrate the spectra with metrological traceability to the International System of Units SI.

Utilizing Laser-Induced Fluorescence to Evaluate the Efficiency of Carbon Dioxide and Diode Lasers in Dentin Sealing after Tooth Preparation: An in-vitro Study.

Adhesive dentistry has made it feasible to design restorations with high aesthetic qualities and little invasiveness. However, the freshly cut dentin after the tooth preparation needs to be sealed to prevent its contaminations, bacterial leakage, and hypersensitivity. Consequently, the immediate dentin sealing (IDS) method has been advised. This study examines different dentinal tubule sealing methods via CO2 laser, diode laser (980-nm) and a two-step self-etch adhesive system applied directly to the fresh cut dentin preceding the placement of the provisional phase. The sealing efficiency of each laser and bond system was evaluated based on the laser-induced fluorescence (LIF) properties and image analysis by scanning electron microscopy. Moreover, the obtained LIF spectra were evaluated using partial least square progression. A two-step adhesive containing a high concentration of S-PRG fillers produced a thick layer that was not perfectly uniform at all sites due to uneven filler distribution in the bond with totally and partially closed dentinal tubules. However, the peaks of the LIF spectra dropped after applying laser because of its sealing effectiveness. Accordingly, CO2 and diode lasers have strong evidence in dentinal tubule sealing and a definitive treatment modality for dentinal hypersensitivity. Moreover, IDS with an adhesive system is superior in occluding dentinal tubules in a biomimetic manner based on its filler content and bioactive properties.

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 dB) and measured LIF spectra with Xe as the working fluid. In the typical measured spectrum (SNR = 26.23 dB) experiment, compared with the Gaussian filter and the Richardson–Lucy (R-L) algorithm, the proposed algorithm demonstrates an increase in SNR of 1.39 dB and 4.66 dB, respectively, along with a reduction in the root-mean-square 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 dB) experiment, the results show that the running time of the proposed algorithm is reduced by about 98% 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.

CH3O Substitution Effect Revisited in the Vibrationally Resolved Laser-Induced Fluorescence Spectra of Methoxycyclohexoxy Radicals.

The oxy-substituted alkoxy radicals have attracted wide attention due to the increasing application of oxygenated volatile organic compounds as fuel additives and solvents. Direct detection of these intermediate radicals is desired for measuring the reaction rate and investigating the oxidation mechanism of organic compounds in the atmosphere. A charge-transfer excited state induced by CH3O substitution was identified in our previous study of 3-methoxy-1-propoxy radical [Xue, J. Phys. Chem. Chem. Phys. 2021, 23, 2586]. As the C-C bonds of chain alkoxy radicals can freely rotate, further studies are needed to understand the mechanism of this long-range charge-transfer effect. In this work, vibrational-resolved laser-induced fluorescence (LIF) spectra of 3- and 4-methoxycyclohexoxy radicals were obtained under jet-cooled conditions. A large red-shift of ∼454 cm-1 of the origin band was observed when the CH3O substituent moved from the δ site to the γ site of the cyclohexoxy radical. The LIF spectra are assigned to 3-cis (e, e) and 4-trans (e, e) conformers, respectively, with the assistance of structural optimization and electron excitation studies conducted at the CAM-B3LYP/6-311++G(d,p) level of theory. Natural transition orbital analysis reveals that the intramolecular charge transfer from the C-O-C p orbital to the radical O p orbital in 3-methoxycyclohexoxy has a strong effect on the radical CO σ → O p excitation and hence results in a spectral change. On the other hand, the spectral effect of CH3O substitution almost vanishes at δ carbon. The results propose a through-bond interaction between CH3O and radical CO groups.

Three-dimensional flow velocity determination using laser-induced fluorescence method with asymmetric optical vortex beams

Laser-induced fluorescence (LIF) Doppler spectroscopy using an optical vortex beam with an asymmetric intensity distribution, referred to as aOVLIF, is proposed as a new method to measure plasma flow velocity. LIF spectra were calculated numerically using typical laboratory low-temperature plasma parameters, and it was revealed that an ion flow across the beam produces a frequency shift of the spectra. This method also has the capability of temperature measurements. The propagation effects of asymmetric optical vortex beams are discussed assuming an actual experiment, and it is found that the sensitivity to the transverse flow velocity is approximately unchanged. The aOVLIF method, which exploits the inhomogeneous phase structure of optical vortices, can be applied to the determination of three-dimensional velocity vectors and promises to enhance the usefulness of conventional LIF spectroscopy using plane waves.

Study of the defect in the CaF2 materials via a laser-induced fluorescence measurement

Analysis of defects in optical materials is crucial for their applicability in cutting-edge optical components. Since calcium fluoride (CaF2) is highly regarded for optical applications, understanding the nature of defects within CaF2 is particularly significant. These defects have been conventionally identified through absorption and photoluminescence (PL) emission studies. In this work, we investigate the defects by measuring laser-induced fluorescence (LIF) spectra over a long irradiation. By decomposing the PL spectrum into multiple Gaussian PL bands, we identify the defects within the CaF2 material. The measurement of irradiation-induced PL can be rationalized by the stabilization of F-centers via the formation of M-centers. PL mapping has been also studied to study the potential link between the surface oxygen contamination of CaF2 samples and polishing techniques.

Optical spectroscopy of the previously unobserved palladium monosulfide (PdS) radical.

The optical spectra of the palladium monosulfide (PdS) molecule in gas phase have been investigated for the first time through laser-induced fluorescence (LIF) and single-vibronic-level (SVL) emission spectroscopies. The I3Σ- - X3Σ- transition system containing 16 vibronic bands was identified in the LIF spectra, covering the energy range of 22 030-23 400cm-1. The spectra with rotational resolution allowed for the determination of the molecular constants in both the ground X and excited I electronic states, involving the spin-orbit splitting, rotational constant, vibrational frequency, and isotope shift. Isotopically resolved SVL emission spectra permitted the observation of the spin-orbit splitting, vibrational frequency, and vibrational isotope shift of the X3Σ-0+,1 and A3Π2,1,0-,0+ states as they transitioned from the excited I state to the vibrational levels of the X and A states. Ab initio calculations presented plenty of the Λ-S and Ω states of PdS below 28 000cm-1 and provided strong support for the assignments of the experimental observation.

High-resolution laser spectroscopy of the [formula omitted][formula omitted] transition in YbOD

Ytterbium monohydroxide (YbOH) and its isotopologues are good candidate molecules for use in the search for physics beyond the standard model. We present a rotational analysis of the Ã2Π1/2−X̃2Σ+ transition in 174YbOD, the deuterated analogue of 174YbOH, based on high-resolution laser-induced fluorescence spectra. The band origin T0= 17993.81014(33) cm−1 was shifted to the red of the 174YbOH origin (T0= 17998.5875(2) cm−1). The ground state rotational parameter is B = 0.2205648(72) cm−1, which compares favourably to the value of 0.2203 cm−1 estimated by isotopically scaling the 174YbOH value of B = 0.245116257(1) cm−1.

Femtosecond laser-induced fluorescence for rapid monitoring of cardiac troponin 1 as a cardiovascular disease biomarker

Medical diagnosis usually requires blood analysis of various biomarkers which are essential for disease detection and health status monitoring. Cardiac troponin 1 (cTn1) is a protein member of the cardiac troponin complex used for the diagnosis of several pathologies associated with cardiomyocyte necrosis. Laser-induced fluorescence (LIF) is a technique with high sensitivity and specificity, and it is one of the most significant developments used as an analytical tool for qualitative and quantitative analysis. The current study investigated the potential application of femtosecond LIF as a novel detection technique for rapid monitoring of cTn1 in clinical analysis. In the present study, the cTn1 (8 ng/ml) was excited over wavelengths ranging from 350 to 400 nm, and the LIF spectra were recorded. The results demonstrated that the maximum fluorescence intensity was observed at an excitation wavelength of 350 nm, with an emitted fluorescence peak centeredat 494 nm. At an excitation wavelength of 350 nm, different concentrations of cTn1 have been investigated and LIF spectra were obtained. The results revealed that the fluorescence peak intensity is concentration-dependent and increases linearly with increasing cTn1 concentration. These findings show that femtosecond LIF presents a unique, highly selective, precise, and direct approach to monitoring cTn1.

Prediction of brown tide algae using improved Gramian angular field and deep learning based on laser-induced fluorescence spectrum

The frequent occurrence of algal blooms has seriously affected the marine environment and human production activities. Therefore, it is crucial to monitor the phytoplankton concentration in water bodies. In this study, a prediction method for brown tide algae using improved Gramian angular field (IGAF) and deep learning based on the laser-induced fluorescence spectrum was proposed. The method combined one-dimensional (1D) fluorescence spectrum with IGAF for image coding. The internal normalizing approach of the original Gramian angle field algorithm was upgraded from local to global, which can increase the difference between samples with various concentrations. Then, we established a novel technique that fully takes into account the Gramian angular difference field and Gramian angular summation field features, allowing it to control the main and sub-diagonal features and successfully convert 1D sequences into images by adding various weight factors. Using depthwise separable convolutional neural network to extract image features helps reduce model training parameters, paired with long short-term memory network to rapidly predict the concentration of brown tide. To confirm the actual performance of the given approach, ablation and contrast experiments were carried out, and the results showed that the method’s regression accuracy, R 2 was 97.8%, with the lowest mean square error and mean absolute error. This study investigated the transformation of 1D spectra into images using IGAF, which not only explored the application of the fluorescence spectrum image coding method for algal regression but also enabled the introduction of the potent benefits of deep learning image processing into the field of spectral analysis.

Black Plastic Waste Classification by Laser-Induced Fluorescence Technique Combined with Machine Learning Approaches

Sensor-based sorting devices commonly used in plastic recycling plants, mainly working in the near infrared range (NIR), are unable to identify black plastics, due to their low spectral reflectance. The aim of this work was to investigate the potentialities offered by laser-induced fluorescence (LIF) technique (spectral range 270–750 nm) for the identification of black polymers inside a plastic waste stream, thus allowing the possibility to build efficient sorting strategies to be applied in recycling plants. Representative samples of black plastics collected among the most utilized in household packaging were selected, constituted by four different types of polymers, i.e., expanded polystyrene (EPS), polystyrene (PS), polypropylene (PP) and high-density polyethylene (HDPE). The acquired LIF spectra were processed using multivariate approaches in order to optimize polymer classification. The developed hierarchical—partial least square-discriminant analysis (Hi-PLS-DA) classification model, showed excellent performances, confirmed by the values of sensitivity and specificity values in prediction, being equal to 1. The correctness of classification obtained by LIF was confirmed by the application of Fourier Transform Infrared spectroscopy (FTIR) on the same samples. The achieved results demonstrated the potential of LIF technique combined with a machine learning approach as sorting/quality control tool of black polymers in recycling plants.Graphical

Detection Experiment of Six Vitamins by Laser-Induced Fluorescence Spectra

Detection Experiment of Six Vitamins by Laser-Induced Fluorescence Spectra

Simple, Fast Nitric Oxide Planar Laser-Induced Fluorescence Model for Computational Fluid Dynamics Applications

The current work demonstrates the efficacy of a simple and fast model for nitric oxide (NO) laser-induced fluorescence (LIF). The model is validated with experimental LIF spectra computed from captured images of fluorescence from a gas cell filled with a known amount of NO. These data are obtained for several segments of the NO fluorescence spectrum. The selected segments encompass LIF lines with rotational quantum numbers appropriate for low-to-moderate temperature flows. The spectra obtained using the current model are also compared to those obtained from other theoretical models, namely, LIFBASE and LINUS. The current model is based on a previously developed version of a two-level fluorescence model and is developed specifically for applications in computational fluid dynamics (CFD) where rapid on-the-fly evaluations are required due to the potentially large number of grid cells for which LIF is being computed. Good agreement between the experimental and theoretical results provides confidence in current LIF modeling for use with CFD. An example application of the current model in a Mach 6.5 hypersonic mixing flowfield is also presented.

Electronic Spectroscopy of Jet-Cooled NdO

Chemi-ionization reactions of the type M + O → MO+ + e- (M = Nd or Sm) are currently being investigated as a method to artificially increase the electron density in the ionosphere for control of micro- and radio wave propagation. Experiments involving the release of atomic Nd into the upper atmosphere have resulted in the production of a cloud that, on excitation by solar radiation, emits green light. It has been assumed that NdO was the carrier of this emission, but the existing spectroscopic data needed for this attribution is lacking. While the electronic spectrum of NdO has been well-characterized at wavelengths greater than 590 nm, relatively little spectroscopic data exist for emission wavelengths in the blue-green spectral range. In this study, spectra for jet-cooled NdO were recorded over the range 15,500-21,000 cm-1. Rotationally resolved laser induced fluorescence and vibronically resolved dispersed laser-induced fluorescence spectra were recorded, and nine new electronically excited states were identified. The data indicate that the electronic spectrum of NdO has relatively few allowed transitions in the green spectral range, casting doubt on the assignment of the Nd high-altitude release cloud green emission to NdO.

Laser-induced fluorescence spectroscopy for kinetic temperature measurement of xenon neutrals and ions in the discharge chamber of a radiofrequency ion source

Application of single-photon absorption laser-induced fluorescence (LIF) spectroscopy for non-intrusive measurement of neutral xenon and singly charged xenon ion kinetic temperatures in the discharge chamber of a gridded radiofrequency ion source is demonstrated. A LIF spectrum analysis approach including hyperfine structure reconstruction and inverse filtering (Fourier deconvolution) is outlined. Special focus is set on optimization of post-deconvolution filtering as well as retracing of deconvolution result imperfection due to hyperfine structure parameter uncertainty, incorrect natural linewidth, and saturation of the LIF signal. The corresponding contributions to the kinetic temperature estimation error are quantified via simulation of spectral lineshapes. Deconvolution of almost unsaturated LIF spectra recorded in the center of the ion source discharge chamber reveals that the neutral xenon and xenon ion kinetic temperatures range between approximately 500 and 700 K and, respectively, 700 and 1000 K depending on the radiofrequency power supplied to the discharge.

Simultaneous measurements of NH2 and major species and temperature with a novel excitation scheme in ammonia combustion at atmospheric pressure

This work reports the first 1D, simultaneous, laser-induced fluorescence (LIF) measurements of the amidogen (NH2) radical concentration and Raman/Rayleigh measurements of major species and temperature in laminar counterflow non-premixed and premixed NH3/H2/N2–air flames. The instrument presents a novel excitation scheme for NH2, which add no complexity to the existing Raman/Rayleigh instrument. The NH2 LIF is excited by three Nd:YAG lasers, temporally stretched to 500 ns using a pulse stretcher, resulting in total energy of ∼ 1 J at 532 nm. LIF spectra collected in NH2 produced from photolysis of NH3, in an oxygen-free environment, match those obtained in the counterflow flames. The NH2-LIF signal is sampled in the 620–630 nm, together with the Raman signal, using the same collection hardware. The weak absorption cross-section at 532 nm is compensated by the high laser energy available, and the long pulse allows repeated excitation and emission from the same molecule, leading to the partial saturation region. A simplified model which neglects quenching, and contributions from other species, but includes Raman crosstalk from H2, N2, and NH3 is proposed and calibrated by comparing measurements and 1D Chemkin simulation of a counterflow flame. Finally, this simplified model was validated in more than 23 flames with varying fuel compositions, strain rates, and non-premixed and premixed flames to assess accuracy and precision. The overall agreement between the measured and simulated NH2 using the same mechanism is within 5%, and the single-shot detection limit is below 100 ppm. NO2-LIF is one of the main interferences to NH2-LIF, and its effects can be negligible on the fuel side, but care only need to be taken on the air side with T < 800 K, in which the maximum interference ∼33 ppm was observed. The accuracy of chemical kinetic models, with an uncertainty of ∼ 20%, limits the accuracy of the proposed NH2 measurements. The technique is best suited to investigate the turbulence-chemistry interaction in turbulent NH3 flames combined with major species and temperature from Raman/Rayleigh scattering, and it can provide useful validation data for the numerical model when the same chemical model is used.

High-resolution isotope-shift spectroscopy of Cd i

We present absolute frequency measurements of the ${}^{1}\text{P}_1 \leftarrow {}^{1}\text{S}_0$ ($229$nm) and ${}^{3}\text{P}_1 \leftarrow {}^{1}\text{S}_0$ ($326$nm) transitions for all naturally occurring isotopes of cadmium. The isotope shifts and hyperfine intervals of the fermionic isotopes are determined with an accuracy of 3.3MHz. We find that quantum interference in the laser-induced fluorescence spectra of the ${}^{1}\text{P}_1 \leftarrow {}^{1}\text{S}_0$ transition causes an error of up to 29(5)MHz in determining the hyperfine splitting, when not accounted for with an appropriate model. Using a King-plot analysis, we extract the field- and mass-shift parameters and determine nuclear charge radius differences for the fermions. The lifetime of the $^1\text{P}_1$ state is determined to be 1.60(5)ns by measuring the natural linewidth of the ${}^{1}\text{P}_1 \leftarrow {}^{1}\text{S}_0$ transition. These results resolve significant discrepancies among previous measurements.

Research on transformer fault diagnosis based on an IWHO optimized MS1DCNN algorithm and LIF spectrum.

Accurate diagnosis of transformer faults can effectively improve the enduring reliability of power grid operation. Aiming at overcoming the problems of long time consumption and low diagnostic rate in the past diagnosis methods, this article designs a laser-induced fluorescence (LIF) detection system, which can be combined with a multi-scale one-dimensional convolution neural network (MS1DCNN) to diagnose transformer fault categories. The structural parameters of MS1DCNN are optimized using the improved wild horse optimizer (IWHO). Electrical fault oil, thermal fault oil, normal oil and locally damped oil are used as raw materials for the experiment. First, the LIF spectral data of the four kinds of oil samples are obtained, and the spectral data obtained are pretreated by standard normal variate (SNV) and multiple scattering correction (MSC), and the dimensions are reduced by linear discriminant analysis (LDA) and kernel principal component analysis (KPCA). Then the dimensionality reduced data are imported into the MS1DCNN algorithm for learning, and the parameters of MS1DCNN are optimized using the IWHO algorithm. Finally, the experiment shows that the efficiency and precision of LIF technology for raw data extraction are higher than for traditional methods; in comparison with the same type of algorithm, MSC has a better preprocessing effect, KPCA has a better dimensionality reduction effect, MS1DCNN has a better prediction effect, and IWHO has a better optimization effect. Compared to them, the MSC-KPCA-IWHO-MS1DCNN model has the best diagnostic ability, with a mean square error (MSE) of 4.9037 × 10-4, mean absolute error (MAE) of 0.0179, and goodness of fit (R2) of 0.9996. Transformer fault intelligent diagnosis is necessary for the sustained and stable operation of power networks.