LIBS application note
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Improved Metal Recycling Industrial processes based on laser induced breakdown spectroscopy (LIBS) can benefit from the use of compact high-repetition-rate solid-state lasers. Bertrand Noharet, Tania Irebo, Carola Sterner, Mikael Ek and Håkan Karlsson Bertrand Noharet, Tania Irebo, Carola Sterner, Mikael Ek and Håkan Karlsson Hübner GmbH & Co. KG, Heinrich-HertzStraße 2, 34123 Kassel Laser-induced breakdown spectroscopy (LIBS) is an atomic-emission spectroscopy technique that enables rapid chemical analysis of a wide range of materials, including metals, semiconductors, glasses, biological tissues, plastics, soils, thin paint coatings, and electronic materials. he LIBS technology has gained increased interest in recent years as a result of the development of more compact including handheld systems that enable in-field use and the construction of tools for on-line material analysis. This development has been made possible by the increased availability of more compact and industrial-grade system components, including lasers and spectrometers. A recent study conducted by the Swedish national research labs Acreo Swedish ICT and Swerea KIMAB, in collaboration with laser manufacturer Cobolt AB, exemplifies this trend and shows how a new class of compact, industrialgrade lasers with multikilohertz pulse-repetition rates enables significant reduction of the footprint of a LIBS system and opens new The Cobolt Tor™ is a compact, high-repetition-rate 1064 nm or 532 nm laser system. opportunities for the use of LIBS to improve efficiency in industrial processes, such as sorting of metals for recycling. The compact pulsed dioded-pumped solid-state (DPSS) laser used in the study gives nice LIBS sig­ als on dirty scrap parts n of Al with penetration depths of > 50 µm at a peak power density of 3.5 GW/cm2. The major strength of the LIBS technique is its ability to perform fast and remote chemical analysis to determine the elemental composition of the tested samples without the need of any sample preparation. The LIBS technology relies on focusing short, high-energy laser pulses onto the surface of a target sample Focussing lens Sample Collecting optics Optical fiber Fig. 1  Schematic illustration of a typical LIBS set-up Physics’ Best  April 2016   © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim to generate a plasma consisting of small amounts of ab­ ated material l (Fig. 1). The extremely high temperatures within the early plasma (more than 100 000 K) cause the ablated material to dissociate into excited atomic and ionic species; as the plasma cools, the characteristic atomic emission lines can be detected by a spectrograph. The method enables fast and sensitive chemical analysis of, in principle, any kind of matter (solid, liquid, or gas). Detection limits are typically in the low parts per million for heavymetal elements. Sample preparation is normally not necessary and the method is also considered essen­ tially nondestructive as only a small amount of the material is removed. Other advantages of LIBS are its ability to provide depth profiles and to remove surface contamination. LIBS is an attractive technology for a wide range of scientific and industrial analytical applications, including metal-content analysis, solar silicon quality control, plant and soil analysis, mining and prospecting, forensic and biomedical studies, and explosives and biological warfare detection. Its potential use in tools for on-line monitoring of industrial processes is particularly inter

tal industry. For example, LIBS can be applied to monitor and optimize critical metallurgical processes (slag or molten metal analysis), to control the quality of metal products (rolls, tubes, foils, and so on), or to analyze and sort metal scrap before recycling. Lasers for LIBS Most laboratory LIBS set-ups have traditionally been based on flashlamp-pumped Q-switched Nd:YAG lasers that deliver pulses with energies of hundreds of milli-joules in short pulse widths (4 to 5 ns) at relatively low pulse-repetition rates, typically 10 to 30 Hz. More recently, industrial fiber lasers have been...

Fig. 3  A measured pulse train for a Cobolt Tor™ 1064 nm laser operating at a repetition rate of 8 kHz generated high-quality LIBS spectra with good signal-to-noise ratios. All the alloying elements that are critical for aluminum scrap classi­ fication can be clearly quantified (Fig. 4). Encouraged by the promising results on reference samples, experiments with dirty scrap samples col­ ected at scrapyards were conl ducted to confirm the practical applicability of a LIBS system based on this compact high-repetitionrate laser. The system was proven to be capable of clearly resolving the...

Fig. 5 LIBS data obtained for two dif- rent aluminum alloys with different ferent scrap samples representing diffe- material compositions. Acknowledgments This work has been conducted with help of Acreo Swedish ICT and Swerea KIMAB. Special thanks to Hakan Toors and Fredrik Lindberg at KIMAB who helped generating SEM images and confocal measurements of the ablation depth profiles. [2] L. Radziemski and D. Cremers, Spectro-chimica Acta Part B 87, 3 (2013) [3] R. Ahmed and M. Aslam Baig, J. Appl. Phys. 106, 033307 (2009) [4] J. D. Winefordner et al., J. Anal. At. Spectrom. 19, 1061 (2004)...