Atomic Line Intensities Research Articles

Using the space-time evolution spectrum to investigate the transmission characteristics of lightning return stroke current

Exploring the physical characteristics of lightning discharge channels based on spectrum can help to reveal the microscopic mechanism of the discharge process and provide a theoretical basis for lightning protection research. According to the spectra of six cloud-to-ground lightning return stroke processes and plasma conduction theory, we investigated the evolution of the total intensity of ionic and atomic lines in the spectra, conductivity, and other parameters along the discharge channel at different stages of the return stroke. The results show that the intensity of ionic lines in the spectrum present an obvious decaying trend with increasing height along the channel during the initial current-rise phase of the return stroke. In the later stages, the decay of ionic line intensity along the channel height slowed down. The intensity of the atomic lines varied slightly with increasing height along the channel during the entire return stroke process. The different space-time evolution characteristics of the spectral line intensity with different excitation energies reflect the differences in the mechanism of light radiation in the core current-carrying and surrounding thermal channels. The spectral characteristics further confirm that the ionic line with higher excitation energy directly relates to the physical process in the core current-carrying channel, and its intensity can roughly reflect the change in current along the channel. The attenuation of the return stroke current along the channel was mainly manifested in the initial stage of the return stroke. The decay rate of conductivity along the channel height is slower than that of the ionic line intensity throughout the return stroke stage, which is related to the channel diameter, it is another key parameter affecting the current transmission in the discharge channel.

Surface hardness imaging of a low-alloy steel using laser-induced breakdown spectroscopy

Conventional tactile hardness testing methods such as Brinell, Rockwell or Vickers rely on direct mechanical contact, which results in significant surface damage and prohibits their application to complex specimen geometries. Furthermore, the sample must have a certain thickness for tactile testing methods to be applied. In this work, we investigated the use of laser-induced breakdown spectroscopy as a fast non-quantitative alternative for visualizing surface hardness gradients. To eliminate the influence of different chemical compositions, we manually heat-treated low-alloy steel pieces cut from the same raw material and batch. By partially quenching a sample piece, we were able to obtain a hardness gradient along the longitudinal axis. We found a positive correlation between the ratio of ionic to atomic line intensities of iron (I Fe II 263.1 nm / I Fe I 358.1 nm) and the mechanical hardness of the sample surface. By scanning the surface and measuring the line intensity ratios, we were able to obtain a spatially resolved map directly correlating with the surface hardness distribution. Additionally, it was observed that the irradiation of laser pulses resulted in significant surface alterations, thereby invalidating subsequent measurements and scans at identical positions.

Modulate the laser phase to improve the ns-LIBS spectrum signal based on orbital angular momentum.

Aiming to enhance the ns-LIBS signal, in this work, we introduced orbital angular momentum to modulate the laser phase of the Gaussian beam into the vortex beam. Under similar incident laser energy, the vortex beam promoted more uniform ablation and more ablation mass compared to the Gaussian beam, leading to elevated temperature and electron density in the laser-induced plasma. Consequently, the intensity of the ns-LIBS signal was improved. The enhancement effects based on the laser phase modulation were investigated on both metallic and non-metallic samples. The results showed that laser phase modulation resulted in a maximum 1.26-times increase in the peak intensities and a maximum 1.25-times increase in the signal-to-background ratio (SBR) of the Cu spectral lines of pure copper for a laser energy of 10 mJ. The peak intensities of Si atomic spectral lines were enhanced by 1.58-1.94 times using the vortex beam. Throughout the plasma evolution process, the plasma induced by the vortex beam exhibited prolonged duration and a longer continuous background, accompanied by a noticeable reduction in the relative standard deviation (RSD). The experimental results demonstrated that modulation the laser phase based on orbital angular momentum is a promising approach to enhancing the ns-LIBS signal.

Non-Gaussian Signal Statistics’ Impact on LIBS Analysis

A detailed study has been carried out to reveal signal statistics’ impact on analysis sensitivity in laser-induced breakdown spectroscopy (LIBS) measurements. For several signals measured simultaneously, it was demonstrated that space-, spectra- and time-integrated plasma emission followed a normal distribution while the spectra- and time-resolved LIBS signal (atomic line intensity, plasma background emissions) distribution functions were biased compared to a Gaussian distribution function. For the first time in LIBS, the impact of a non-Gaussian distribution function on the limit of detection (LOD)’s determination has been studied in detail for single-shot spectra as well as for averaged spectra. Here, we demonstrated that the non-symmetrical distribution of the LIBS signals influenced the estimated LODs, so knowledge of a LIBS signal’s distribution function provides more reliable results, and the analysis sensitivity can be wrongly estimated if Gaussian distribution is presumed.

Studying the effect of the argon flow introduced into the arc discharge in the atomic-emission spectrometry of powdered samples using the spillage-injection method

Atomic emission spectral analysis of a powder sample by the method of spillage-injection into the plasma of an arc discharge burning in air is accompanied by the formation of cyanide, nitride and oxide compounds which form molecular bands in the spectrum thus impeding measuring the intensity of the analytical lines of the elements to be determined. Feeding an argon flow into the arc discharge can reduce the amount of spectral interference and increase the plasma temperature, which promotes more a complete evaporation of the analyzed sample injected into the arc discharge and, accordingly, increases the degree of ionization of the elements and the intensity of ion spectral lines. The aim of the study was to develop a device for argon introduction into the arc discharge zone and simultaneous sample delivery by a spillage-injection method, as well as to study the effect of argon consumption on arc discharge parameters and emission spectra of powder samples. The argon input device (up to 2.25 L/min) is developed on the basis on glass funnels, the geometric dimensions of which are selected with the goal of gaining the maximum intensity of spectral lines and reduced intensity of molecular bands at the minimal argon consumption. The study carried out on a «Grand Potok» spectrometer demonstrated that with an increase in argon consumption, the intensity of SiO molecular bands decreases, the plasma temperature increases by 350 – 540 K, and the intensity of ion and atomic lines with the ionization energy above 8 eV increases by more than 4.7 and 2.9 times, respectively. The developed device can be used in analysis of geological materials to improve the metrological characteristics of the results of atomic emission spectral analysis.

Correlation between the Channel Discharge Current and Spectrum of a Single-Stroke Lightning Flash to Canton Tower

The intense current of lightning plasma can emit radiation across various parts of the electromagnetic spectrum. Spectral observation is an effective means to understand the radiation characteristics of lightning channels at different wavelengths. In this context, the spectra and channel current of a single-stroke lightning flash to Canton Tower were acquired from the Tall-Object Lightning Observatory in Guangzhou using a slitless high-speed spectrograph and a Rogowski coil. Spectral correction was applied for enhanced spectral analysis. The relationship between the intensities of different spectral lines and the directly measured current of the lightning channel was investigated for the first time. The results indicated that the duration of the ionic lines in the visible region can be up to one millisecond during the entire discharge process, which is clearly longer than the duration reported in previous research. There always exists a good exponential relationship (y = axb) between the intensities of ionic lines and the channel current with an exponent value (b) very close to 2 and with a coefficient of determination (R2 value) higher than 0.99, whereas the exponential relationship between many atomic lines and the channel current has an exponent value clearly smaller than 2 with a relatively lower R2 value, which implies that the intensities of ionic lines are evidently associated with the square of the current, while the intensities of atomic lines have relatively weak exponential correlation with the current. We also preliminarily verified this conclusion with temperature derived from the ionic and atomic lines. The results indicated that due to the time integral of the current squared, the cooling rate of the temperature derived from the ionic lines in the channel core is not significant when the current decreases, while the cooling rate of the temperature derived from the atomic lines of the surrounding corona sheath channel presents a pronounced decline with a decrease in current.

Continuation of investigation of effect of O2 in plasma gas on parameters of nitrogen microwave-induced plasma optical emission spectrometry

We studied the effect of O2 content in the range up to 80% in plasma gas on the plasma characteristics, the analyte signal and the intensity of the molecular species in the nitrogen microwave-induced plasma (MIP). The plasma temperature decrease from 3.9·103 to 3.3·103 K with increasing O2 content. Mg (II)/Mg (I) intensity ratio decrease from 1.02 to 0.18, the electron density decrease from 6.6·1012 to 4·1011 cm−3. The intensity of N2 (1+ system), N2 (2+ system), N2+, NH, NO, and OH intensities increases to a certain content, and then decrease (NH) or remain constant (OH) when O2 is added. The effect of O2 content on the intensity of several atomic and ionic emission lines (covering Esum values from 1.6 to 14.7 eV) of 22 elements has been studied. The line intensity was suppressed over the entire energy range. It was shown that the O2 addition increased the limit of detection (LOD) by 1.2–4 for lines with Esum of 1.5–4 eV and by 50–60 times for lines with Esum of 4–15 eV.

DIAGNOSTICS OF PLASMA OF ELECTRIC ARC DISCHARGE BETWEEN ASYMMETRIC SINGLE-COMPONENT Cu AND Ni ELECTRODES

In this work, the radial distributions of parameters of plasma with copper and nickel vapours admixtures in positive column of electric arc discharge were investigated by optical emission spectroscopy. The plasma temperature was determined by the Boltzmann plot technique on the basis of absolute values of radiation intensity of both copper and nickel atomic spectral lines. Concentrations of both kinds of metal atoms of electrode origin were determined by the method of absolute intensities of the corresponding spectral lines of radiation of such plasma.

Diagnostics of laser-induced plasma from a thin film of oil on a silica wafer

In this study, plasma induced by a nanosecond Nd:YAG laser on thin oil films deposited on a silica wafer was characterized by evaluating the main plasma parameters. Spatially and temporally integrated spectral measurements were performed under experimental conditions optimized for elemental analysis of trace metals in oil. Time-resolved values of the spectral line intensities, electron number density, and plasma temperature were obtained from time-integrated measurements by subtracting averaged spectra recorded at different time delays. The electron number density was estimated using the Stark broadened profile of the hydrogen Balmer alpha line. Ionization temperatures were derived from Mg ionic to atomic line intensity ratios. The obtained apparent values of time-resolved plasma parameters were in the range of 1.1?1017 cm-3 (1.5 ?s) to 1.5?1016 cm-3 (4 ?s) and 9400 K (3 ?s) to 7200 K (5 ?s), depending on the delay time. Emission spectra of C2 and CN molecules were used to evaluate the rotational and vibrational temperature.

Simultaneous analysis of long-pulse laser irradiated plasma-facing materials (PFMs) microstructure and hardness by in-situ laser Opto-ultrasonic dual detection (LOUD)

Laser-induced transient heat load events such as edge localized mode (ELM) could induce recrystallization, grain growth, surface degradation, and hardness changes. In this regard, we used the long-pulse laser beams with power densities ranging from 0.165 to 1.909 GW m−2 to simulate transient heat load events for pure tungsten and tungsten heavy alloy (WHA) materials. The investigated samples showed that pure tungsten exhibited a higher recrystallization threshold, steady grain growth, and less surface hardness deterioration than WHA. However, the real-time simultaneous analysis of structural and mechanical properties such as matrix elements, grain size, surface degradation, and hardness changes is challenging in this domain. Therefore, in this study, we utilized a novel laser Opto-ultrasonic dual detection (LOUD) multimodal technique that integrates the benefits of laser-induced breakdown spectroscopy (LIBS) and laser ultrasonic testing (LUT) for simultaneous and in-situ detection of elemental information, grain size and hardness. The preliminary results showed that the variation in hardness is well correlated with the LIBS calibration curve formed by the ionic to atomic line intensity ratio and plasma electron temperature (Te). Despite the different matrix compositions of both samples, the observed increase in the value of Te with hardness justifies the Saha-Eggert relation. The coefficient of determination (R2 ≥ 0.970) value in the calibration curve and Te for hardness evaluation showed the goodness of the fitted model. Furthermore, the correlation of grain size with ultrasonic acoustic attenuation (α) was analyzed by the pulse-echo technique of the ultrasonic waveform for investigated samples. The results showed that grain size is also directly associated with acoustic attenuation with R2 > 0.989. The findings showed that the regression coefficient has a good approximation, which demonstrates the preciseness and potential ability of the LOUD technique for in-situ grain size and hardness analysis.

A spectral comparison of lightning discharge plasma and laser-induced air plasma

The high time-resolved spectrum of natural lightning is obtained by a slitless spectrograph. The spectrum of natural lightning is compared to the spectrum of laser-induced air plasma. The results show that the spectra of lightning and the spectra of laser-induced air plasma are similar, but they also have some differences. In the superimposed spectrum of lightning, the intensities of atomic lines are far stronger than those of ionic lines, and the continuous spectrum in the whole wavelength region is very strong. However, in the spectrum of laser-induced air plasma, the intensities of atomic lines are similar to those of ionic lines, and there is almost no continuous spectrum in the near-infrared region. In addition, the Hα line is strong in the lightning spectrum but very weak in the spectrum of laser-induced air plasma. The temperature, electron density, and conductivity are calculated, and their evolution with time is also given. The differences in the three physical parameters between lightning and laser-induced air plasma are analyzed. In addition, the reasons of spectral differences have been explained. These results will provide an important reference for the simulation of the lightning spectrum.

Collisional-radiative recombination of Ne-=SUP=-++-=/SUP=- and Ne-=SUP=-+-=/SUP=- ions with electrons in the decaying plasma of a low-pressure barrier discharge

The results of an experimental study and simulation of radiation generated by the processes of collisional-radiative recombination of neon ions Ne+ and Ne++ with electrons of the decaying plasma are presented. Plasma was created by a barrier discharge in a cylindrical glass tube with electrodes on its surface. Experimental conditions: neon pressure 0.65 Torr, electron density at the initial stage of the afterglow [e] ~ (1-5)·1011 cm-3. The main attention is paid to the comparative analysis of the collisional-radiative recombination of Ne+ and Ne++ ions based on the numerical solution of coupled differential equations for the densities of charged and long-lived excited particles and the electron temperature, taking into account the main elementary processes in decaying neon plasma. Comparison of the model solutions with the intensities of ionic and atomic spectral lines measured by the multichannel photon counting method indicates the need to refine the dependence of the rate of collisional-radiative recombination on the ion charge. Keywords: dielectric barrier discharge, doubly charged ions, collisional-radiative recombination, decaying plasma, elementary processes.

Ударно-радиационная рекомбинация ионов Ne-=SUP=-++-=/SUP=- и Ne-=SUP=-+-=/SUP=- c электронами в распадающейся плазме барьерного разряда низкого давления

The results of an experimental study and simulation of radiation generated by the processes of collisional-radiative recombination of neon ions Ne+ and Ne++ with electrons of the decaying plasma are presented. Plasma was created by a barrier discharge in a cylindrical glass tube with electrodes on its surface. Experimental conditions: neon pressure 0.65 Torr, electron density at the initial stage of the afterglow [e] ≈ (1 - 5) • 1011 cm-3. The main attention is paid to the comparative analysis of the collisional-radiative recombination of Ne+ and Ne++ ions based on the numerical solution of coupled differential equations for the densities of charged and long-lived excited particles and the electron temperature, taking into account the main elementary processes in decaying neon plasma. Comparison of the model solutions with the intensities of ionic and atomic spectral lines measured by the multichannel photon counting method indicates the need to refine the dependence of the rate of collisional-radiative recombination on the ion charge.

Spatial characterization of ns-laser induced Tungsten plasma in air using laser induced breakdown spectroscopy

The laser induced plasma (LIP) of tungsten is studied using space-resolved laser induced breakdown spectroscopy (SR-LIBS). In the present work a Q-switched Nd:YAG laser working at wavelength of 532 nm having maximum energy of 600 mJ and pulse duration of 7 ns with repetition rate of 1 Hz is used to generate the plasma onto the target sample surface. The LIP is generated at four different incident laser energy of 25, 50, 75 and 100 mJ. The spectra recorded from the different location of the LIP is analyzed to get the spatial distribution of plasma emission intensity of atomic and ionic transitions, plasma temperature and electron density. The plasma temperature is determined using the Boltzmann plot from the WI lines and that of the electron density estimated using Stark broadened profile of WI transition at 430.2 nm. The intensity of atomic lines as well as plasma parameters attain the maximum value at a distance ranging from 1.6 mm to 2.0 mm away from the target surface for the incident laser energy of 25 mJ and 50–100 mJ, respectively. The thermal conduction towards the solid target and radiative cooling of the plasma and conversion of thermal energy into kinetic energy is responsible for the decrease in plasma temperature towards the plasma edge away from the target surface whereas the direct ejection of low velocity neutrals around the target surface is responsible for lower temperature. Both these plasma parameters are also studied at incident laser energy of 25, 50, 75 and 100 mJ. The validity of the local thermodynamic equilibrium (LTE) is studied by Mc-Whirter criteria and diffusion length is estimated at different location of the plasma to understand the effect of inhomogeneous nature of LIP on the validity of LTE. The branching ratio method is employed to study optical thin condition of the LIP at different axial location as function of energy. From this an optimized spatial window is identified for the LIBS studies.

Dependence of Optical Emission Spectra on Argon Gas Pressure during Modulated Pulsed Power Magnetron Sputtering (MPPMS)

Modulated pulsed power magnetron sputtering (MPPMS) of titanium was investigated as a function of argon gas pressure using optical emission spectroscopy (OES). Delays in discharge and the formation of comb-like discharge current waveforms due to splitting and pulsing were observed with a decrease in pressure. This observation corresponds to the evolution from MPPMS condition to deep-oscillation-magnetron-sputtering (DOMS)-like condition by changing discharge gas pressure. The optical emission intensities of the ionic species (Ar+ and Ti+) increased as the comb-like current waveforms were formed with decreasing Ar pressure. This behavior showed a marked contrast to that of the neutral species (Ar and Ti). The Ar pressure dependence of OES was revealed to be due to the plasma build-up stage, which is the initial generation process of plasma discharge in pulsed dc magnetron sputtering, from the temporal profile for the atomic-line intensities of the optically emitting species in MPPMS and DOMS-like plasmas.

Comparison of matrix effects on atomic emission spectrometers with nitrogen microwave induced plasma

The creation and implementation of new sources of sample excitation and spectrometers based on them into the practice of analytical laboratories raises many questions for researchers about the obtained analytical characteristics of new equipment and analysis methods. The most important characteristics of any method include detection limits, accuracy and reproducibility of the results obtained. Matrix elements can have a significant effect on these parameters. The paper shows a comparison of the change in the intensities of analytical lines of elements in the presence of matrix elements with ionization potentials of 5.13 - 10.48 eV (Na, Cu, Pb, Cd, Zn, In, Ga, Bi) in the concentration range of 0 - 1 wt %. on commercially available atomic emission spectrometers with microwave plasma Grand-MP ("VMK-Optoelektronika") and Agilent MP-AES 4100 (Agilent Technologies). It is shown that the magnitude of the matrix effect in these excitation sources depends on the ionization potential of the matrix element and the total energy of the analyte line. A significant effect of matrix elements with a concentration of up to 1% wt. on the intensity of spectral lines of atoms and ions of the sample. Elements with medium and high ionization energies practically do not affect the intensity of atomic spectral lines of impurity elements and lead to a decrease in the intensity of ionic lines. The influence of easily ionized elements is more pronounced - both depressing and amplifying effects are observed, probably caused by both a change in the concentration of electrons in the plasma, leading to a linear change in the equilibrium between atoms and ions, and a decrease in the plasma temperature. An increase in the power supplied to the plasma on the Grand-MP spectrometer leads to a decrease in the effect of easily ionized elements on the intensity of the spectral lines of the elements. It is shown that the plasma in the Grand-MP spectrometer has better resistance to matrix influences as compared to the Agilent MP-AES 4100, which is associated with a large plasma volume and a higher input power.

Study of the dependence of the structure and luminescence of the discharge channel in a discharge with a liquid cathode from the electrochemical properties of a liquid cathode

In the present work, the structure of the discharge channels glow of a discharge with a liquid cathode at different pH values of the solution at a given concentration of alkali metal (Na) ions in the solution is investigated by the methods of emission spectroscopy and high-speed photography. The dependence of the atomic sodium line intensity in the emission spectrum of the discharge plasma from the pH value of the solution is investigated. The dependence of the discharge channels filaments shape on the presence of sodium impurities in them is found. The spatial and temporal inhomogeneity of sodium luminescence in the emission spectrum of the discharge channel of a discharge with a liquid cathode at different pH values of the solution is studied. Its connection to the mechanism of sodium transfer into the gas phase is discussed.

Correlation between surface hardness of α-alumina samples and their spectroscopic parameters

The aim of this paper is to correlate between surface hardness of α-alumina samples with their spectroscopic parameters. A structural analysis for the alumina samples using an X-ray diffractometer (XRD) and a Raman spectroscopy was achieved where the grain size and the phase of crystallization of the samples were determined. A morphological analysis was also done by a scanning electron microscope (SEM) showing the porosity of the less hard sample. For mechanical analysis, nano-indenter (hardness and Young modulus) and micro hardness tester were used. For plasma analysis, Laser Induced Breakdown Spectroscopy (LIBS) technique has been employed. In this study, we have confirmed the previous found correlations in which a linear evolution of the ionic to atomic line intensity ratio and electronic temperature with surface hardness was obtained. This linear behavior was also obtained with electron density and vibrational temperature of AlO radical giving the alternative to determine the hardness of an unknown α-alumina using one of these spectroscopic parameters.

Plasma molecular species and matrix effects in the Hummer cavity microwave induced plasma optical emission spectrometry

The effect of matrix elements with ionization potentials from 5.72 to 10.48 eV (In, Ga, Cu, Pb, Cd, Bi, Zn, P) on atom and ion excitation temperatures, magnesium ratio, plasma molecular species and analytical signals more 30 trace elements in atmospheric pressure nitrogen microwave induced plasma (Agilent 4100 AES MP) have been studied. The concentration of matrix elements was varied in the range of 0–1% w·w−1. It was shown that in the Hammer cavity, intensities of atomic and ionic lines with similar energies change in a similar way with increasing concentration of the matrix element. It was shown that, in general, the matrix effect doesn't correlate with the temperature. The Mg(II)/Mg(I) and both N2+/OH and N2+/N2 correlates with the ionization potential of the matrix element and reflect the degree of its manifestation.

Impact of microstructural properties on hardness of tungsten heavy alloy evaluated by stand-off LIBS after PSI plasma irradiation

The key issue in tokamak is change of physical properties of plasma facing materials, such as tungsten due to extreme conditions and long pulse operation. Practically, it is difficult to analyze hardness changes online through conventional methods. Hence, an online monitoring technique is much desired which measures hardness changes in fusion devices. In this study, laser induced breakdown spectroscopy (LIBS) is used as in-situ monitoring tool to measure hardness of tungsten heavy alloy (97W–2Ni–1Fe) samples after exposure to different irradiation of plasma ranging from 0.108 to 1.00 MW/m2. The exposure of PSI plasma beam is a key factor which give rise to pronounced change in crystallographic estimation, microstructural properties and surface hardness. The X–ray diffraction study revealed modification in the structure caused, by variation in the peak intensity, crystal size, dislocation line density and micro-strains upon plasma irradiation. The change in crystallographic measurements and surface hardness are well correlated with irradiated PSI power densities. Moreover, the hardness influence on LIBS intensity of tungsten heavy alloy (WHA) was carried out. The LIBS calibration curves were formed by utilizing the ratio of ionic to atomic line intensities of tungsten versus the Vickers hardness. The ratio of ionic to atomic spectral emission line intensity and plasma electron temperature (Te), significantly increases with hardness. The obtained Pearson correlation coefficient (R2) values (in case of calibration curve and plasma temperature) in measuring hardness of all investigated samples have good approximation which indicate the preciseness of LIBS approach. The achieved results in the present study by in-situ LIBS system confirmed its potential ability to estimate the hardness of WHA more efficient than other conventional method.