Single-pulse Laser-induced Breakdown Spectroscopy Research Articles

Determination of lead in water using laser ablation–laser induced fluorescence

The detection sensitivity of laser-induced breakdown spectroscopy (LIBS) is improved by coupling it with a laser-induced fluorescence method. A waterjet sample containing 500 ppm of Pb as an analyte was ablated by a 266 nm, frequency-quadrupled Q-switchedNd:YAG laser at an energy of ~ 260 μJ. After a short delay the resulting plume was re-excited with a 283.306 nm, nanosecond pulse dye laser at energies ranging from 45 to 100 nJ. The limit of detection (LOD) of lead in water was determined both by the single-pulse LIBS technique and Laser Ablation coupled with Laser-Induced Fluorecence (LA–LIF) method. It was found to be 75 ppm in the case of single-pulse LIBS and 4.3 ppm for LA–LIF. When the resonant pulse was detuned from the transition wavelength the LA–LIF signal disappeared demonstrating the resonant selectivity of this technique.

Double pulse laser-induced breakdown spectroscopy of explosives: Initial study towards improved discrimination

Detecting trace explosive residues at standoff distances in real-time is a difficult problem. One method ideally suited for real-time standoff detection is laser-induced breakdown spectroscopy (LIBS). However, atmospheric oxygen and nitrogen contributes to the LIBS signal from the oxygen- and nitrogen-containing explosive compounds, complicating the discrimination of explosives from other organic materials. While bathing the sample in an inert gas will remove atmospheric oxygen and nitrogen interference, it cannot practically be applied for standoff LIBS. Alternatively, we have investigated the potential of double pulse LIBS to improve the discrimination of explosives by diminishing the contribution of atmospheric oxygen and nitrogen to the LIBS signal. These initial studies compare the close-contact (< 1 m) LIBS spectra of explosives using single pulse LIBS in argon with double pulse LIBS in atmosphere. We have demonstrated improved discrimination of an explosive and an organic interferent using double pulse LIBS to reduce the air entrained in the analytical plasma.

Laser-induced breakdown spectroscopy at a water/gas interface: A study of bath gas-dependent molecular species

Single-pulse laser-induced breakdown spectroscopy has been performed on the surface of a bulk water sample in an air, argon, and nitrogen gas environment to investigate emissions from hydrogen-containing molecules. A microplasma was formed at the gas/liquid interface by focusing a Nd:YAG laser beam operating at 1064 nm onto the surface of an ultra-pure water sample. A broadband Echelle spectrometer with a time-gated intensified charge-coupled device was used to analyze the plasma at various delay times (1.0–40.0 μs) and for incident laser pulse energies ranging from 20–200 mJ. In this configuration, the dominant atomic spectral features at short delay times are the hydrogen H-alpha and H-beta emission lines at 656 and 486 nm, respectively, as well as emissions from atomic oxygen liberated from the water and air and nitrogen emission lines from the air bath gas. For delay times exceeding approximately 8 μs the emission from molecular species (particularly OH and NH) created after the ablation process dominates the spectrum. Molecular emissions are found to be much less sensitive to variations in pulse energy and exhibit a temporal decay an order of magnitude slower than the atomic emission. The dependence of both atomic hydrogen and OH emission on the bath gas above the surface of the water was studied by performing the experiment at standard pressure in an atmospheric purge box. Electron densities calculated from the Stark broadening of the H-beta and H-gamma lines and plasma excitation temperatures calculated from the ratio of H-beta to H-gamma emission were measured for ablation in the three bath gases.

Sequential-Pulse Laser-Induced Breakdown Spectroscopy of High-Pressure Bulk Aqueous Solutions

Sequential-pulse (or dual-pulse) laser-induced breakdown spectroscopy (DP-LIBS) with an orthogonal spark orientation is described for elemental analysis of bulk aqueous solutions at pressures up to approximately 138 x 10(5) Pa (138 bar). The use of sequential laser pulses for excitation, when compared to single-pulse LIBS excitation (SP-LIBS), provides significant emission intensity enhancements for a wide range of elements in bulk solution and allows additional elements to be measured using LIBS. Our current investigations of high-pressure solutions reveal that increasing solution pressure leads to a significant decrease in DP-LIBS emission enhancements for all elements examined, such that we see little or no emission enhancements for pressures above 100 bar. Observed pressure effects on DP-LIBS enhancements are thought to result from pressure effects on the laser-induced bubble formed by the first laser pulse. These results provide insight into the feasibility and limitations of DP-LIBS for in situ multi-elemental detection in high-pressure aqueous environments like the deep ocean.

Dual-pulse Laser Induced Breakdown Spectroscopy for analysis of gaseous and aerosol systems: Plasma-analyte interactions

Dual-pulse LIBS has been previously investigated to a large extent on solid and liquid phase analytes, where it has been demonstrated to significantly enhance atomic emission signal intensity, and more importantly, to enhance the analyte peak-to-base and signal-to-noise ratios. This study focuses on the effects of an orthogonal dual-pulse laser configuration on the atomic emission response for both purely gaseous and calcium-based aerosol samples. The gaseous sample consisted of purified (i.e. aerosol free) air, from which nitrogen and oxygen spectral emission lines were analyzed. Measurements for the gaseous system resulted in no notable improvements with the dual-pulse configuration as compared to the single-pulse LIBS. Experiments were also conducted in purified air seeded with calcium-rich particles, which revealed a marked improvement in calcium atomic emission peak-to-base (∼ 2-fold increase) and signal-to-noise ratios (∼ 4-fold increase) with the dual-pulse configuration. In addition to increased analyte response, dual-pulse LIBS yielded an enhanced single-particle sampling rate when compared to conventional LIBS. Transmission measurements with respect to the plasma-creating laser pulse were recorded for both single and dual-pulse methods over a range of temporal delays. In consideration of the spectroscopic and transmission data, the plasma-analyte interactions realized with a dual-pulse methodology are explained in terms of the interaction with the initially expanding plasma shock wave, which differs between gaseous and particulate phase analytes, as reported in a recent study [V. Hohreiter, D.W. Hahn, Calibration effects for laser-induced breakdown spectroscopy of gaseous sample streams: analyte response of gas-phase species versus solid-phase species, Anal. Chem. 77 (2005) 1118–1124].

Elemental chemical analysis of submerged targets by double-pulse laser-induced breakdown spectroscopy

Double-pulse laser-induced plasma spectroscopy (DP-LIPS) is applied to submerged targets to investigate its feasibility for elemental analysis. The role of experimental parameters, such as inter-pulse delay and detection time, has been discussed in terms of the dynamics of the laser-induced bubble produced by the first pulse and its confinement effect on the plasma produced by the second laser pulse. The analytical performance of this technique applied to targets in a water environment are discussed. The elemental analysis of submerged copper alloys by DP-LIPS has been compared with conventional (single-pulse) LIBS in air. Theoretical investigation of the plasma dynamics in water bubbles and open air has been performed.

Spectroscopic and shadowgraphic analysis of laser induced plasmas in the orthogonal double pulse pre-ablation configuration

This work focuses on the study of the plumes obtained in the double pulse orthogonal Laser Induced Breakdown Spectroscopy (LIBS) in the pre-ablation configuration using both spectroscopic and shadowgraphic approaches. Single and double pulse LIBS experiments were carried out on a brass sample in air. Both the distance of the air plasma from the target surface and the interpulse delay were varied (respectively in the range 0.1–4.2 mm and up to 50 μs) revealing a significant variation of the plasma emission and of the plume-shock wave dynamical expansion in different cases. The intensity of both atomic and ionized zinc lines was measured in all the cases, allowing the calculation of the spatially averaged temperature and electron density and an estimation of the ablated mass. The line intensities and the thermodynamic parameters obtained by the spectroscopic measurements were discussed bearing in mind the dynamical expansion characteristics obtained from the shadowgraphic approach. All the data seem to be consistent with the model previously proposed for the double pulse collinear configuration where the line enhancement is mainly attributed to the ambient gas rarefaction produced by the first laser pulse, which causes a less effective shielding of the second laser pulse.

Quantitative determination of wear metals in engine oils using LIBS: The use of paper substrates and a comparison between single- and double-pulse LIBS

A comparison between single- and double-pulse LIBS for the quantitative elemental analysis of used engine oils has been performed. Paper substrates have been utilised for the analysis and are shown to provide better limits of detection (LODs), no splashing and easier sample handling compared to the previously reported experiments using laminar liquid jets and static liquid surfaces. Single-pulse LIBS analysis of oil on paper substrates has had on average 2× better LODs than was obtained using flowing liquid jets, while double-pulse LIBS showed 4× improvement. Single-pulse LIBS has been found preferable for the analysis, as the use of an additional laser in double-pulse LIBS yielded only a minor improvement while adding substantially to the complexity and cost of the system.

Dual-pulse laser induced breakdown spectroscopy: Time-resolved transmission and spectral measurements

Spectral analysis of laser-induced plasmas for surface ablation has demonstrated the possibility of analyte signal enhancement with dual-pulse configurations as compared with traditional single-pulse LIBS. Using an orthogonal dual-pulse arrangement, measurements were performed using glass microscope slides to allow both spectral analysis as well as optical transmission measurements. Order of magnitude enhancements in Mg and Si atomic emission signal peak intensities were recorded along with similar enhancements of the continuum emission for dual-pulse LIBS as compared to single-pulse. Peak-to-base measurements showed a roughly 50% increase, while signal-to-noise ratios were enhanced by a factor of 2–3. Temporal analysis of the measured transmitted laser pulse waveforms showed no significant differences between dual-pulse and single-pulse LIBS configurations, providing additional insight into the possible laser coupling processes for the dual-pulse configuration.

Single Pulse-Laser Induced Breakdown Spectroscopy in aqueous solution

In this paper the flexibility of Laser Induced Breakdown Spectroscopy (LIBS) has been proved for the analysis of water solutions. The plasma is generated directly in the bulk of a water solution by a Q-switched Nd:YAG laser (1064). The emission signal of four different solutions has been studied: AlCl3, NaCl, CaCO3 and LiF. The basic mechanisms influencing the emission signal and the experimental tricks for the optimization of the detection mode have been pointed out.

Effects of sample temperature in femtosecond single-pulse laser-induced breakdown spectroscopy.

As much as tenfold atomic emission enhancements have been observed in experiments combining nanosecond (ns) and femtosecond (fs) laser pulses in an orthogonal dual-pulse configuration for laser-induced breakdown spectroscopy (ns-fs orthogonal dual-pulse LIBS). In the examination of one of several potential sources of these atomic emission enhancements (sample heating by a ns air spark), minor reductions in atomic emission and as much as 15-fold improvements in mass removal have been observed for fs single-pulse LIBS of heated brass and aluminum samples. These results suggest that, although material removal with a high-powered, ultrashort fs pulse is temperature dependent, sample heating by the ns air spark is not the source of the atomic emission enhancements observed in ns-fs orthogonal dual-pulse LIBS.

Single-pulse laser-induced breakdown spectroscopy of samples submerged in water using a single-fibre light delivery system

Using a novel laser-induced breakdown spectroscopy set-up, accurate quantitative analysis of samples submerged in liquids has been demonstrated. The measurements were conducted using a single-fibre plus plastic tube assembly of 20 m length. This delivered the ablation laser light pulse and a buffer gas flow to the sample surface, and collected the light emitted by the micro-plasma for analysis. No distil optics were used at the sample end of the fibre. Argon, nitrogen and compressed air were used as buffer gases; while the rare gas resulted in slightly better signal-to-noise ratios, most analytical measurements were carried out with nitrogen for convenience and to provide comparability with in-air measurements. Detection limits and reproducibility were comparable to those achieved for the same samples placed in standard ambient air, with all other experimental conditions unchanged. In standard steel samples, detection limits of 310±45, 325±48 and 455±55 ppm for Cr, Mn and Si, respectively, could be achieved. Pattern recognition algorithms were used to identify, for classification, spectra of specimen submerged in turbid and non-transparent liquids.

LIBS using dual- and ultra-short laser pulses.

Pre-ablation dual-pulse LIBS enhancement data for copper, brass and steel using ns laser excitation are reported. Although large enhancements are observed for all samples, the magnitude of the enhancement is matrix dependent. Whereas all of the dual-pulse studies used ns laser excitation we see interesting effects when using ps and fs laser excitation for single-pulse LIBS. LIBS spectra of copper using 1.3 ps and 140 fs laser pulses show much lower background signals compared to ns pulse excitation. Also, the atomic emission decays much more rapidly with time. Because of relatively low backgrounds when using ps and fs pulses, non-gated detection of LIBS is shown to be very effective. The plasma dissipates quickly enough using ps and fs laser pulses, that high pulse rates, up to 1,000 Hz, are effective for increasing the LIBS signal, for a given measurement time. Finally, a simple near-collinear dual-pulse fiber-optic LIBS probe is shown to be useful for enhanced LIBS measurements.

Enhancement of Aluminum, Titanium, and Iron in Glass Using Pre-Ablation Spark Dual-Pulse LIBS

In this paper, we report the first enhanced emission for elements in a nonmetal or nonconducting matrix, glass, with the use of a pre-ablation spark. The glass samples used in this work are prototypes of samples used to immobilize inorganic waste at the Savannah River Site Vitrification Facility. We have found that using a pre-ablation spark results in larger signal enhancements, 11- to 20-fold for titanium, aluminum, and iron in glass compared to the metal under the same experimental conditions. We also demonstrate that this method is more sensitive than single-pulse LIBS experiments for the direct solid sampling of vitrified waste glass.