Determination of Stark Shifts and Widths Using Time Resolved Laser-Induced Breakdown Spectroscopy (LIBS) Measurements (original) (raw)
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… Acta Part B: Atomic …, 2005
This paper is part of a more general study aimed to the determination of the best experimental procedures for reliable quantitative measurements of Fe-Mn alloys by LIBS. In this work, attention is pointed on the self-absorption processes, whose effect deeply influences the LIBS measurements, reflecting in non-linear calibration curves. The effect of self-absorption on the line intensity can be quantified by defining a self-absorption coefficient, that measures the deviation of the line intensity from the linear extrapolation of the curve of growth in the optically thin regime. The authors demonstrated in a previous paper that self-absorption coefficients could be calculated once the electron density of the plasma is known and the Stark coefficients of the lines are available. However, when the Stark coefficients of the lines of interest are not known, a different approach is needed. In this work a new method for evaluation of self-absorption coefficients in LIBS measurements is presented, which does not require the knowledge of Stark coefficients. In order to understand the basic principles and setting out the theoretical tools that will be used for the analysis of the alloys, a preliminary study was done on pure Mn; LIBS spectra were acquired in different experimental conditions, at different laser energies and different delays after the laser irradiation of the sample. Moreover, collinear double pulse measurements were also performed. Analytical relations were derived and experimental procedures devised for evaluation of the self-absorption coefficients of several Mn lines, which are important for characterization and control of the experimental conditions in which the analysis is performed.
We built a collinear dual-pulse laser-induced breakdown spectroscopy (DP-LIBS) system to study the aluminum (Al) plasma emission by installing a pair of Nd: YAG lasers operating at 266 and 1064 nm. The spectral intensities of selected aluminum doubly-ionized lines were employed to evaluate the optical emission spectra. The influences of the energy ratio of two pulsed lasers on the LIBS intensity for different Al doubly-ionized spectral lines were investigated. The de-excitation rate parameters of the excited ion and the electron impact excitation were computed using the analytical formulas proposed by Smeets and Vriens. The transition probabilities and energy states were computed using Hibbert's configuration interaction, computer package (CIV3). By solving the coupled rate equations including 1s 2 2s 2 2p 6 ns ( 2 S), 1s 2 2s 2 2p 6 np ( 2 P), 1s 2 2s 2 2p 6 nd ( 2 D) (n = 3-5) and 1s 2 2s 2 2p 6 nf ( 2 F) (n = 4, 5) states, the level population densities were computed. We also proposed a theoretical population model in order to investigate the effectiveness of the various processes that might affect the population of the upper levels in Al plasma by using the rate coefficients. In addition, the population densities for the 19 upper levels were also computed. Good compatibility between the experimental and the theoretical model data had been observed. Our results might be significant as reference data for the optimization of the DP-LIBS spectrometry and diagnostics of laser produced plasmas.
Stark broadening measurement of Al II lines in a laser-induced plasma
2014
Laser induced plasma was a light source for the study of Stark broadening parameters of singly charged aluminum ion lines. Plasma electron number density in the range (0.3-2.3) Â 10 23 m À 3 was measured from the Stark width of the hydrogen H α impurity line, while the electron temperature between 6500 and 17,500 K was determined from relative intensities of Fe II, Mg I and Al II spectral lines using the Boltzmann plot technique. The experimental Stark widths were compared with other experiments and theories, which include semiclassical results and data evaluated from the modified semiempirical formula.
Influence of working pressure and lasing energy of Al plasma in laser-induced breakdown spectroscopy
Iraqi Journal of Physics (IJP)
Aluminum plasma was generated by the irradiation of the targetwith Nd: YAG laser operated at a wavelength of 1064 nm. Theeffect of laser power density and the working pressure on spectrallines generating by laser ablation, were detected by using opticalspectroscopy. The electron density was measured using the Starkbroadening of aluminum lines and the electron temperature byBoltzmann plot method it is one of the methods that are used. Theelectron temperature Te, electron density ne, plasma frequencyand Debye length increased with increasing the laser peakpower. The electron temperature decrease with increasing gaspressure.
A comparison of single and double pulse laser-induced breakdown spectroscopy of aluminum samples
Spectrochimica Acta Part B-atomic Spectroscopy, 2002
Single and double pulse laser-induced breakdown spectroscopy (LIBS) was carried out on aluminum samples in air. In the case of double pulse excitation, experiments were conducted by using the same laser source operated at the same wavelength (1064 nm in most cases here presented). A lowering of the second pulse plasma threshold was observed, together with an overall enhancement in line emission for the investigated time delay between the two pulses (40-60 ms). The laser-induced plasma originated by a single and double pulse was investigated near ignition threshold with the aim to study possible dynamical mechanisms in different regimes. Currently available spectroscopic diagnostics of plasma, such as the line broadening and shift due Stark effects, have been used in the characterization in order to retrieve electron densities, while standard temperature measurements were based on Boltzmann plot. Plasma relevant parameters, such as temperature and electron density, have been measured in the plasma decay on a long time scale, and compared with crater shape (diameter and inferred volume). The comparison of double with single pulse laser excitation was carried out while keeping constant the energy per pulse; the influence of laser energy was investigated as well. Results here obtained suggest that use of the double pulse technique could significantly improve the analytical capabilities of LIBS technique in routine laboratory experiments. ᮊ
Laser-Induced Breakdown Spectroscopy for Determination of Spectral Fundamental Parameters
Applied Sciences, 2020
In this review, we report and critically discuss the application of LIBS for the determination of plasma-emission fundamental parameters, such as transition probabilities, oscillator strengths, Stark broadening and shifts, of the emission lines in the spectrum. The knowledge of these parameters is of paramount importance for plasma diagnostics or for quantitative analysis using calibration-free LIBS methods. In the first part, the theoretical basis of the analysis is laid down; in the second part, the main experimental and analytical approaches for the determination by LIBS of the spectral line spectroscopic parameters are presented. In the conclusion, the future perspectives of this kind of analysis are discussed.
Journal of the European Optical Society: Rapid Publications, 2014
In this paper, the influence of heating and cooling samples on the optical emission spectra and plasma parameters of laser-induced breakdown spectroscopy for Titanium 64, Inconel 718 super alloys, and Aluminum 6061 alloy is investigated. Samples are uniformly heated up to approximately 200°C and cooled down to-78°C by an external heater and liquid nitrogen, respectively. Variations of plasma parameters like electron temperature and electron density with sample temperature are determined by using Boltzmann plot and Stark broadening methods, respectively. Heating the samples improves LIBS signal strength and broadens the width of the spectrum. On the other hand, cooling alloys causes fluctuations in the LIBS signal and decrease it to some extent, and some of the spectral peaks diminish. In addition, our results show that electron temperature and electron density depend on the sample temperature variations.
Spectrochimica Acta Part …, 2001
. We present here the results of the application of laser induced breakdown spectroscopy LIBS to a sample of a solid aluminum᎐lithium alloy, in which the latter component is at a very low concentration and whose proportion should be determined. The samples were placed in a vacuum chamber filled with a controlled xenon atmosphere, and the emission lines of this element were used to determine the electronic density and temperature of the laser generated plasma. Then, by means of a specially designed algorithm, it is possible to quantify the lithium content in q3 Ž . the sample. The laser produced aluminum᎐lithium alloy plasma was generated by a pulsed Nd :YAG laser 50 mJ the pulse repetition frequency used was varied according to requirement from 1 to 20 Hz. Satisfactory results were obtained for the analytical determination of lithium contents in aluminum᎐lithium alloys. The lithium concentration was determined in values as low as 300᎐400 ppm. ᮊ
Plasma Sources Science and Technology
We present results of experimental and theoretical studies of the Stark broadening of the LiI 460 nm spectral line with forbidden components and of the isolated 497 nm line. Plasma was induced by Nd:YAG laser radiation at 1064nm with pulse duration ∼4.5ns. Laser-induced plasma was generated in front of the alumina pellet, with some content of Li 2 CO 3 , placed in a vacuum chamber filled with argon under reduced pressure. Plasma diagnostics was performed using the laser Thomson scattering technique, free from assumptions about the plasma equilibrium state and its composition and so independently of plasma emission spectra. Spatially resolved spectra with Li lines were obtained from the measured, laterally integrated ones applying the inverse Abel transform. The Stark profiles were calculated by computer simulation method assuming a plasma in the local thermodynamic equilibrium. Calculations were performed for experimentally-inferred electron densities and temperatures, from 1.422×10 23 to 3.55×10 22 m −3 and from 1.96eV to 1.04eV, respectively. Our studies show very good agreement between experimental Stark profiles and those computer simulated.