Plasma-grating-induced breakdown spectroscopy

Characterization of multilayer coatings of aluminium, tungsten and molybdenum on steel substrate using laser-induced breakdown spectroscopy

The sensitivity of double-pulse laser-induced breakdown spectroscopy (DP-LIBS) in the detection of trace elements in samples was confirmed to be superior to that of single-pulse laser-induced breakdown spectroscopy (SP-LIBS). However, DP-LIBS is not economical because it requires two lasers. A DP-LIBS system based on beam splitting was proposed in this work, and the experimental equipment was used to analyze Y, La, Yb, and Dy elements in rare earth ores. The comparison of spectral line intensities and sensitivities of rare earth elements in rare earth ore samples between DP-LIBS and SP-LIBS was studied. The results show that the enhancement of the spectral line signal intensity of DP-LIBS is more than two times compared with that of SP-LIBS. The time evolution of signal intensities of four rare earth element characteristic lines (Y II 437.49 nm, La II 433.37 nm, Yb II 328.94 nm, and Dy II 353.17 nm) was given. The enhancements of signal intensities were found to be due to that the plasma temperature of DP-LIBS is increased by more than 500 K. The limits of detection of Y, La, Yb, and Dy were 40.97, 104.09, 47.13, and 56.25 ppm for SP-LIBS and can be reduced to 21.19, 56.93, 28.69, and 36.41 ppm for DP-LIBS. It is showed that DP-LIBS based on a single Nd:YAG laser can better improve the signal intensity and sensitivity of Y, La, Yb, and Dy elements in rare earth ore samples.

Developing dielectric capacitors with both a high power density and a high energy density for application in power electronics has been a long-standing challenge. Glass-ceramics offer the potential of retaining the high relative permittivity of ceramics and at the same time of exhibiting the high dielectric breakdown strength and fast charge/discharge rate of glasses, thus producing concurrently high power and energy densities in a single material. In this work, glass-ceramics are fabricated to achieve simultaneously high power and energy densities, high efficiency, and thermal stability by tuning the glass crystallization process via a suitable nucleating agent and a high oxygen partial pressure. Under the same practical charge-discharge test conditions, the as-prepared glass-ceramics combine the high energy density of ceramics and ultrafast discharge rate of glasses, producing the highest power density among glass- and ceramic-based dielectric materials. This work demonstrates the significant potential of achieving both high power and energy densities in glass-ceramics by optimizing the glass crystallization process.

We have designed the physical model and numerical algorithm for the simulations of acoustic wave propagation from the source induced by relaxation of a femtosecond plasma grating formed by two crossing filaments in atmospheric air. The model is based on the wave equation with the wave velocity depending on the transverse temperature variation. The algorithm is based on the fine resolution (\({\approx }2\,\upmu \text {m}\)) numerical grid employed for the description of the plasma channel substructures in the course of femtosecond filamentation. We have shown that the femtosecond plasma grating emits the superposition of two acoustic signals after plasma recombination. One acoustic signal is represented by an isotropic cylindrical waveform with the characteristic spatial scale equal to the filament diameter (100–200 \(\upmu \text {m}\)) while the other has the spatial scale equal to the plasma grating period in the range \(20{-}40\,\upmu \text {m}\). This second wave propagates in the direction parallel to the axis of plasma grating modulation. Based on the simulations, we suggested the noninvasive method for the plasma grating period and the beam convergence angle detection.

Laser induced breakdown spectroscopy (LIBS) measurement of a thin Cu(In,Ga)Se2 (CIGS) absorber layer was performed under the conditions of open air and argon (Ar) gas jet flow (25 L min−1). A second harmonic Q-switched Nd:YAG laser (λ = 532 nm, τ = 5 ns, top-hat profile) was employed for the ablation of co-evaporated CIGS samples. The use of an Ar gas jet for the LIBS measurement of CIGS thin films leads to two significant differences from the open air measurement results that are important from the precision point of view: (i) the increase of signal intensity and (ii) decrease of relative standard deviation (RSD) of measured intensity or intensity ratios. From calculation of the degree of intensity enhancement, it was shown that the enhancement of signal intensity is primarily due to the increase of plasma temperature and electron density under Ar buffer gas environment. It was also found that in addition to the influence of Ar gas itself the gasdynamic effects of the Ar gas jet contribute significantly to the reduction of RSD.

The optical emission of plasma on industrial steel samples induced by Laser Ablation-Spark Discharge-Optical Emission Spectroscopy (LA-SD-OES) and by Laser-Induced Breakdown Spectroscopy (LIBS) is investigated and correlated to the volume of ablated steel material. The 36 steel samples investigated have an iron content C(Fe) above 94 wt%. The excitation energy in LIBS (laser pulse of 55 mJ) and in LA-SD-OES (laser pulse of 5 mJ and spark discharge of 50 mJ) is the same. In LA-SD-OES, the optical emission of plasma and the size of ablation craters are very similar for all samples and a linear calibration curve for Mn is measured (R2 = 0.99). In LIBS, however, a pronounced dependence of the plasma emission and of the crater volume on the steel matrix is observed and calibration curves show a strong cross-sensitivity to other elements such as Si (matrix effect). The hardness, grain size, and phase of steel samples are analyzed to correlate the matrix effect in LIBS measurements to a physical property of the specimen. The different behavior for LA-SD-OES and LIBS is probably due to different processes of sampling and plasma excitation. From our results we conclude that LA-SD-OES enables for the element analysis of industrial steel largely independent of composition and structure of samples while in LIBS the matrix effect has to be taken into account.

Ablation enhancement and plasma shielding effects during multiple pulses irradiation with different femtosecond laser repetition rates

We report, for what we believe to be the first time, on the feasibility of remote time-resolved filament-induced breakdown spectroscopy (FIBS) of biological materials. The fluorescence from egg white and yeast powder, induced by femtosecond laser pulse filamentation in air, was detected in the backward direction with targets located 3.5 m away from the detection system. The remarkably distinct spectra of egg white and yeast allow us to propose that this technique, time-resolved FIBS, could be potentially useful for remote detection and identification of harmful biological agents.

The application of machine learning (ML) has accelerated the development of laser-induced breakdown spectroscopy (LIBS) in soil analysis. However, analyzing remote LIBS data in real time using ML is challenging due to several factors. Firstly, building robust ML models requires extensive calibration datasets, which are not always possible with limited LIBS experimental data. Secondly, matrix effects can worsen LIBS performance, and changes in sample physical properties or the apparatus can impact the distribution and intensity of emission lines. These issues may lead to concept drift in real-time/online data streaming, causing the relationship between the input and the target spectra to change over time. Consequently, an ML model designed for one LIBS system may not apply to another. To conquer these challenges, we propose a framework based on transfer learning to use limited experimental data and adapt to the emission line variation in the LIBS streaming. A model is first pre-trained using a large labelled source dataset and then fine-tuned with new experimental measurements to classify soil samples. LIBS measurements are conducted with variations in sample properties and experimental parameters to simulate differences in remote LIBS sensors. The collected spectra are fed into the model by chunks, and data evolution is dynamically learned by self-balanced learning to self-adapt to the domain shift. The proposed framework is found effective in improving classification accuracy during data streaming by implementing transfer learning and supporting adaptation compared to the literature. The code of the proposed method is available in the GitHub at <uri xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">https://github.com/kelci2017/LIBS_streaming</uri> .

The detection limit of trace metals in liquids has been improved greatly by laser-induced breakdown spectroscopy (LIBS) using solid substrate. A paper substrate and a metallic substrate were used as a solid substrate for the detection of trace metals in aqueous solutions and viscous liquids (lubricating oils) respectively. The matrix effect on quantitative analysis of trace metals in two types of liquids was investigated. For trace metals in aqueous solutions using paper substrate, the calibration curves established for pure solutions and mixed solutions samples presented large variation on both the slope and the intercept for the Cu, Cd, and Cr. The matrix effects among the different elements in mixed solutions were observed. However, good agreement was obtained between the measured and known values in real wastewater. For trace metals in lubricating oils, the matrix effect between the different oils is relatively small and reasonably negligible under the conditions of our experiment. A universal calibration curve can be established for trace metals in different types of oils. The two approaches are verified that it is possible to develop a feasible and sensitive method with accuracy results for rapid detection of trace metals in industrial wastewater and viscous liquids by laser-induced breakdown spectroscopy.

Laser-induced breakdown spectroscopy (LIBS), which is also known as laser-induced plasma spectroscopy (LIPS), is a very promising spectral analysis technique for detecting elemental composition. The possibility of remote operation of LIBS is one of the properties, which expands the application scope of this technique. The remote LIBS technique is based on a long-range lens. With the increase of focusing distance, it is difficult to tightly focus laser pulse due to the diffraction limits. The size of focusing spot increases with focusing distance increasing. This will require extremely high laser energy. Femtosecond laser filamentation due to optical Kerr effect can be applied to the remote LIBS. During the filament propagation, the waist of laser beam is close to a constant value. The laser intensity inside the filament is about 1013 W/cm2 (intensity clamping). The intensity is sufficient to ablate sample and produce the plasma. It can overcome the influence of the diffraction limit in nanosecond LIBS. Although many researchers have studied the femtosecond geometrical focusing and femtosecond filamentation LIBSs, the spectral characteristics have not been completely understood. In this paper, we study the femtosecond laser filament-induced Cu plasma spectroscopy. Femtosecond laser system is an ultrafast Ti:sapphire amplifier (Coherent Libra). The full-width at the half maximum is 50 fs at a wavelength of 800 nm with a repetition rate of 1 kHz and its output energy is 3.5 mJ. A quartz lens with a focal length of 1 m is used to focus the laser to generate a filament channel. The spectral intensity of produced Cu plasma along the filament channel is measured by using the optical emission spectroscopy, and the distribution of Cu(I) intensity versus the distance between sample and focused lens is obtained. The results indicate that in a longer distance range along the filament, plasma spectroscopy has stronger emission due to the intensity clamping effect in femtosecond laser filamentation. In addition, we also calculate the plasma temperature and electron density by using the Boltzmann plot and the Stark broadening. The plasma temperature and electron density along the filament channel can be divided into three main regions: region 1) from 950 mm to 970 mm, in which the plasma temperature and electron density increase with the increase of distance; region 2) from 970 mm to 1030 mm, in which the change of plasma excitation temperature is opposite to the change of electron density; region 3) from 1030 mm to 1050 mm, in which the plasma temperature and electron density decrease with the increase of distance.

A hybrid PEMFC/supercapacitor device with high energy and power densities based on reduced graphene oxide/Nafion/Pt electrode

Temporal-resolved characterization of laser-induced plasma for spectrochemical analysis of gas shales

Li ion battery (LIB) and electrochemical capacitor (EC) are considered as the most widely used energy storage systems (ESSs) because they can produce a high energy density or a high power density, but it is a huge challenge to achieve both the demands of a high energy density as well as a high power density on their own. A new hybrid Li ion capacitor (HyLIC), which combines the advantages of LIB and Li ion capacitor (LIC), is proposed. This device can successfully realize a potential match between LIB and LIC and can avoid the excessive depletion of electrolyte during the charge process. The galvanostatic charge-discharge cycling tests reveal that at low current, the HyLIC exhibits a high energy density, while at high current, it demonstrates a high power density. Ragone plot confirms that this device can make a synergetic balance between energy and power and achieve a highest energy density in the power density range of 80 to 300 W kg−1. The cycle life test proves that HyLIC exhibits a good cycle life and an excellent coulombic efficiency. The present study shows that HyLIC, which is capable of achieving a high energy density, a long cycle life and an excellent power density, has the potential to achieve the winning combination of a high energy and power density.

Laser-Induced Breakdown Spectroscopy in open-path configuration for the analysis of distant objects