Application of LIBS: Elemental mapping

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Scan analysis by Laser-Induced Breakdown Spectroscopy (LIBS) is usually performed as sampling in the series of single points (ablation craters), in one, two, or even three directions. The spatial (lateral and depth) resolution is then determined by the size, depth and spacing of the ablation craters. Tightly focused short wavelength laser pulses enable production of both small in diameter and depth ablation craters. However, for the smallest LIBS ablation craters, the emission intensities mainly in single-pulse configuration are usually low, and not sufficient especially for minor and trace elements detection. Double-pulsed LIBS techniques may significantly enhance the signal even if a small amount of material per pulse is ablated. Therefore, double-pulse LIBS instrumentation equipped with UV ablation lasers and IR lasers in reheating mode seem to be suitable for achieving low detection limits with high spatial-resolution. LIBS ablation chambers enable further improvement of figures of merit using the atmosphere of noble gases [1]. Because of the fact that it represents a relatively simple way for fast chemical analysis (even in situ), LIBS has several interesting applications, including e.g., compositional mapping of geological samples. The LIBS potential for discrimination of geological materials using principal component analysis (PCA) was recently examined [2]. Such approach can also be applied in stand-off mode as it was demonstrated e.g., in cases of fast classification of brick samples or fast identification of biominerals [3, 4]. In laboratory conditions, LIBS is a promising alternative to much more complicated, expensive, and slower laser-ablations connected to inductively coupled plasma mass spectroscopy (LA-ICP-MS) techniques [5]. Moreover, LIBS can be effectively combined with X-ray computed tomography (CT). CT provides structure information and a 3D model of the sample, in which materials of different physical properties are distinguished, and LIBS can identify the elemental composition of these materials [6]. Setups with implementation of an autofocus algorithm (for example based on the evaluation of the image sharpness) enable scanning of samples even with rough surfaces in fully automatic mode [7]. An acoustic signal can be used for the internal standardization during elemental mapping. The change in the optical emissions during the ablation was successfully compensated by normalization to the square power of the acoustic signal in the interval of 290-340 nm [8]. Between biominerals, LIBS elemental mapping was applied to bones, teeth, and urinary stones. Double-pulse LIBS was optimized for microspatial analyses of fossils and recent snake vertebrae to identify osteitis deformans phases [9]. Multi-elemental mapping of a prehistoric bear tooth dentine showed seasonal fluctuations and proved the migration of this bear between his hibernaculum location and the place where the fossils were found [10]. The correlation between the distribution of selected elements in urinary stones made it possible to estimate the proportions of particular minerals. These results can be used for comprehensive evaluation of the emergence and growth of urinary stones [11]. LIBS elemental mapping can also be applied in order to obtain information about transport and storage of nutritional or toxic elements in plant compartments. Several studies were focused on the accumulation of heavy metals in leaves, roots, or stems [12-15]. Due to high LIBS sensitivity for detection of nanoparticles, promising results were also obtained in biological applications in connection with the study of distribution of the nanoparticles labeled proteins [16]

Laser-Induced Breakdown Spectroscopy; Self Absorption; Laser-Produced Plasma

NOVOTNÝ, K.; HRDLIČKA, A.; KAISER, J.

1. 1. 2016

978-16-3484-194-8

Horizons in World Physics

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