Mohamad Sabsabi

Quantitative Analysis of Aluminum Alloys by Laser-Induced Breakdown Spectroscopy and Plasma Characterization:

Laser-induced breakdown spectroscopy has been applied to perform elemental analysis of aluminum alloy targets. The plasma is generated by focusing a pulsed Nd:YAG laser on the target in air at atmospheric pressure. Such a plasma was characterized in terms of its appearance, emission spectrum, space-integrated excitation temperature, and electron density. The electron density is inferred from the Stark broadening of the profiles of ionized aluminum lines. The temperature is obtained by using Boltzmann plots of the neutral iron lines. Calibration curves for magnesium, manganese, copper, and silicon were produced. The detection limits are element-dependent but are on the order of 10 ppm.

Enhanced laser-induced breakdown spectroscopy using the combination of fourth-harmonic and fundamental Nd:YAG laser pulses

Abstract We have studied the combination of fourth-harmonic (266 nm) and fundamental (1064 nm) Nd:YAG laser pulses of the same irradiance. On a metallic target (Al), a sequence of ultraviolet (UV) and near-infrared (NIR) pulses produces deeper craters and can lead under certain conditions to analyte signal enhancements larger than those obtained with a NIR–NIR sequence. Compared to a single NIR pulse, signal enhancements by factors of approximately 30 for the Si I 288.16-nm line and 100 for the Al II 281.62-nm line were observed with double pulses of the same total energy. This effect correlates with a substantial increase in plasma temperature, with ionic lines and lines having a higher excitation energy experiencing a larger enhancement. Moreover, the optimal pulse separation is found to be larger for ionic than for neutral lines (∼3 compared to ∼0.1 μs). Another finding of this study concerns the combination of two different wavelengths (266 and 1064 nm) in a single ‘mixed-wavelength’ pulse, a scheme that also leads to an enhanced laser-induced breakdown spectroscopy (LIBS) sensitivity. It is proposed that the double-pulse and mixed-wavelength approaches are both capable of temperature and signal enhancement for the same reason: a larger portion of laser energy is absorbed in the plasma region containing the analyte atoms, instead of being absorbed at the sample surface or in the atmosphere.

Temporal characterization of femtosecond laser pulses induced plasma for spectrochemical analysis of aluminum alloys

Abstract This paper reports studies on time-resolved space-integrated laser induced breakdown spectroscopy (LIBS) of plasmas produced by ultrashort laser pulses at atmospheric pressure, on aluminum alloy targets. The temporal behavior of specific ion and neutral emission lines of Al, Mg and Fe has been characterized. The results show a faster decay of continuum and spectral lines, and a shorter plasma lifetime than in the case of longer laser pulses. Spectroscopic diagnostics were used to determine the time-resolved electron density, as well as the excitation and ionization temperatures. In comparison with plasmas produced by ns laser pulses, the plasma generated by ultrashort pulses exhibits a faster thermalization. Analytical performances of fs-LIBS were also evaluated. Linear calibration curves for minor elements (Mg, Fe, Si, Mn, Cu) presented in aluminum alloys were obtained. The limits of detection are in the parts per million (ppm) range and are element-dependent.

Quantitative analysis of pharmaceutical products by laser-induced breakdown spectroscopy

Abstract In this paper, the capabilities of laser-induced breakdown spectroscopy (LIBS) for rapid analysis of multi-component pharmaceutical tablets are illustrated using several examples. The atomic line emission from an element present only in a particular component of the tablet (for instance, emission of phosphorus from the drug, or of magnesium from the lubricant) enables the quantitative analysis of that component. It is also demonstrated that simple schemes can significantly improve the analytical performance of LIBS in this context. In particular, internal standardization with a carbon line was found to enable the correction of a matrix effect, apart from improving the precision of measurement. Furthermore, an improvement in the linearity of calibration was observed when the plasma continuum emission was used as internal standard. Finally, in the case of drugs containing halogen species (e.g. F or Cl), producing the plasma in a helium atmosphere caused a seven to eight-fold increase of the signal-to-background ratio, thus improving sensitivity. These data illustrate the strengths of LIBS for fast at-line assessment of the reliability of pharmaceutical manufacturing processes.

Analysis of solids using laser-induced plasma spectroscopy in double-pulse mode

Abstract We investigate plasmas formed from solid aluminium alloys in air using a Nd:YAG laser in double-pulse mode, in view of the possibility of enhancing analyte line emissions. In particular, time-resolved studies of emission characteristics and plasma properties are carried out. It is found that the Al II 281.6 nm line is considerably enhanced when using a double-pulse burst instead of a single pulse of equal energy. However, the electron density is found to be approximately the same in both cases, and the plasma temperature is less than 10% higher with the double-pulse burst. The line enhancement is rather explained by the formation of a larger volume of emitting gas. This, in turn, can be linked to a greater ablated mass, as well as to the presence of a preplasma into which the second laser pulse is absorbed. The influence of the interpulse interval on the peak intensity of the Al II line and of several neutral lines of different elements is also studied. For neutral lines, a maximum enhancement factor of 3–4 is attained with an interval in the range 0.5–1 μs. Finally, it is found that the relative standard deviation of 20 consecutive intensity measurements is reduced by a factor of 2–3 when going from single- to double-pulse mode.

Laser-induced breakdown spectroscopy (LIBS)

Laser-induced breakdown spectroscopy (LIBS) is an emerging technique for materials analysis that is rapidly maturing and is becoming increasingly accepted as an important tool in analytical chemistry. LIBS is also advancing as a technology as new commercial instruments are becoming available. The core attributes of (1) real-time analysis; (2) no sample preparation; (3) high sensitivity; (4) high specificity for materials identification; (5) sensitivity to all chemical elements in each laser shot; as well as (6) uncommon versatility of point, standoff, as well as underwater-sensing provides a strong argument that LIBS will make a significant impact on science and society. A bibliometric study of the LIBS literature shows clearly that the importance and the number of application areas related to LIBS and laser-based techniques continues to grow. The driving force for this growth appears to be its rapid and remote analysis capabilities for a wide variety of sample types, including the analysis where the requirement for little or no sample preparation is important and the consumption of very small amounts of the sample is critical. Additionally, the relative ease with which LIBS can be combined with other techniques, particularly molecular techniques such as Raman spectroscopy is an advantage. For proof of the impact that LIBS is already making, one needs to go no further than to learn about the next Mission toMars scheduled for 2011/2012 where LIBS is the prime chemical analytical tool of choice. This special issue on LIBS presents the latest progress in this rapidly evolving spectroscopic technique. The 18 articles represent a good balance between fundamental research on the LIBS phenomenology and the applied use of this technique. The papers presented indicate to the reader the active areas in the LIBS field. For example, research is focused on improving the sensitivity of the technique shows that the approach of double-pulse is still of interest. The understanding of physical phenomenon at the early stage of the plasma or the comparison between singleand double-pulse is still attracting further research. While Nd:YAG lasers operating at the fundamental wavelength 1,064 nm or its harmonics are most used for the laser-induced plasma generation in LIBS applications; some papers are focused on the use of the CO2 laser at 10.6 μm. In some cases, the use of this infrared laser may present benefits which can be further exploited. The analysis of slurries is a field of application where LIBS can offer a powerful tool for real-time analysis as the current analytical approaches in this field by conventional This article was published in the special issue Laser-Induced Breakdown Spectroscopy with Guest Editors Jagdish P. Singh, Jose Almirall, Mohamad Sabsabi, and Andrzej Miziolek.

Towards quantitative depth-profile analysis using laser-induced plasma spectroscopy: investigation of galvannealed coatings on steel

Abstract Laser-induced plasma spectroscopy (LIPS) is applied to depth-profile analysis, with the particular goal of examining how LIPS depth profiles can be fully calibrated. For this purpose, we concentrate on the representative case of galvannealed coatings on steel (i.e. annealed zinc-coated steel). In particular, a method is proposed wherein the second derivative of the zinc intensity profile enables the determination of the coating/substrate interface position. Calibration for the major elements (iron and zinc) is based on a non-linear relationship between the iron-to-zinc line intensity ratio and the iron-to-zinc concentration ratio. Quantitative depth profiles of three elements (Al, Fe and Zn) are obtained for two galvannealed samples. The iron profiles are found to be in broad agreement with those obtained by transmission electron microscopy/energy dispersive X-ray spectrometry.

An evaluation of a commercial Échelle spectrometer with intensified charge-coupled device detector for materials analysis by laser-induced plasma spectroscopy ☆

Abstract In this work we evaluate the performance of a commercial Echelle spectrometer coupled with an intensified charge-coupled device (ICCD) detector for the analysis of solid samples by laser-induced plasma spectroscopy (LIPS) in air at atmospheric pressure. We compare results obtained in aluminum alloy samples with this system and with a ‘conventional’ Czerny-Turner spectrometer coupled to an intensified photodiode array (IPDA). We used both systems to generate calibration curves and to determine the detection limit of minor elements, such as Mg, Cu, Si, etc. Our results indicate that no significant differences in terms of analytical figures of merit exist between the Echelle/ICCD system and a conventional Czerny-Turner spectrometer with IPDA. Moreover, measurements of plasma temperature and electron density using the two assemblies give, in general, very similar results. In the second part of this work, we aim to present a critical view of the Echelle spectrometer for LIPS applications, by drawing up the balance sheet of the advantages and limitations of the apparatus. The limitations are either inherent to the dispersion method, or result from the dynamic range of the detector. Moreover, the minimum ICCD readout time does not allow a fast data acquisition rate. On the other hand, the Echelle spectrometer allows complete elemental analysis in a single shot, as spectral lines of major, minor and trace constituents, as well as plasma parameters, are measured simultaneously. This enables a real-time identification of unknown matrices and an improvement in the analytical precision by selecting several lines for the same element.

Determination of isotope ratios using Laser-Induced Breakdown Spectroscopy in ambient air at atmospheric pressure for nuclear forensics

Laser-Induced Breakdown Spectroscopy (LIBS) is currently a subject of great interest in spectroscopy and is being considered for the design of a field portable unit for nuclear safeguard inspection, because it allows a high level of portability and versatility while identifying the elements and materials of interest. Field portable technologies and methods are sought to provide simple, inexpensive, and fast analysis of materials in the mining, construction, and other industries. However, the level of portability needed for this particular application imposes some restrictions on the choice of many of the core components used in a low cost LIBS handheld sensor. This means that relatively low-performance components, such as a low-energy laser source and a low cost, low resolution spectrometer, must be considered to fulfil these conditions. In addition, the market price of such a portable device should be as low as possible to increase the breadth of potential end users and allow the deployment of multiple units for security enhancement. The present paper describes the determination of isotope ratios using Laser-Induced Breakdown Spectroscopy in air at atmospheric pressure for partially resolved uranium-235/uranium-238 and hydrogen/deuterium isotope shift lines in such conditions. Using a Partial Least Square (PLS1) regression, it is possible to build a model that enables the accurate determination of the isotopic ratio under conditions where the application of traditional univariate approaches for hydrogen and uranium would not be achievable without the use of ultra high resolution spectrometer. In addition, the application of PLS1 regression to determine the uranium-235/uranium-238 and deuterium/hydrogen isotopic ratios between 0 and 1 mass fraction was also successfully demonstrated. The performance obtained with such a LIBS sensor configuration demonstrates the possibility of integrating all of the required components in a small portable handheld system.

Investigation of resonance-enhanced laser-induced breakdown spectroscopy for analysis of aluminium alloys

Resonance-enhanced laser-induced breakdown spectroscopy (RELIBS) was investigated with the aim to improve the limit of detection of trace elements in the context of elemental analysis of aluminium alloys. A Q-switched Nd:YAG laser pulse (7 ns, 1064 nm) was used for ablation of the samples and was followed, after a suitable delay, by an Optical Parametric Oscillator (OPO) laser pulse (7 ns), tuned at 396.15 nm, to resonantly excite the aluminium host atoms. In particular, the Mg I 285.21 nm and Si I 288.16 nm lines were observed in the acquisition spectral window. We investigated the influence of the main experimental parameters, namely, the excitation wavelength, the interpulse delay and the ablation and excitation fluences, on the signal-to-noise ratio for the Mg I 285.21 nm line. We found that, at low ablation fluences, typically less than a few J cm−2, the Mg signal at 285.21 nm achieved using RELIBS was significantly enhanced when compared to LIBS using the same ablation fluence. At fluences higher than 8 J cm−2, the effect of the excitation pulse became unnoticeable and similar results were observed for both approaches. The optimum conditions were achieved for an interpulse delay of about 30 ns, an ablation fluence of about 3.8 J cm−2 and an excitation fluence of about 1.1 J cm−2. The corresponding absolute LoDs were 0.7 and 50 fg, for Mg and Si, respectively, using RELIBS. When using LIBS, they were 4 and 128 fg, instead. Finally, the applicability of RELIBS in the context of a minimally destructive elemental analysis is discussed.