Laser-induced plasma and laser-induced breakdown spectroscopy (LIBS) in China: The challenge and the opportunity

Abstract

Professor Ronger Zheng Laser-induced plasma as a spectroscopic emission source was introduced only two years after the invention of the laser. By focusing a pulse delivered by a ruby laser on the surface of a solid target, Brech and Cross in 1962 first observed optical emission following the laser impact [1], which later had been further identified as the emission from the plasma produced during the laser ablation process of the impacted target. Spectroscopic analysis of the plasma emission immediately demonstrated its huge potential for direct chemical analysis by showing a rich spectrum consisting of specific lines from ions, atoms as well as molecules in the ablation plume [2]. The simplicity of the original concept leads to the intrinsic advantages of the analytical technique developed later according to the above mentioned pioneer works and generally called nowadays, laser-induced breakdown spectroscopy (LIBS). The versatility of laser ablation process enables LIBS to directly analyze all kinds of materials, whether solid, liquid or gas. Sampling and excitation by laser pulse together with detection of optical emission are fully compatible with stand-off operation. On the other hand, the ability of a laser beam to be tightly focused provides microanalysis feature of the technique. Last but not least, LIBS shares multiple elemental analysis capability with other analytical techniques based on emission spectroscopy. Staying a laboratory curiosity up to the 1980’s, LIBS has found its first applications with the developments in Los Alamos conducted by Radziemski and Cremers on the detection of hazardous airborne trace metallic or nonmetallic elements [3, 4]. The development in the 1990’s was more spectacular thanks to the technological progresses realized in laser, in spectrometer and in detector [5]. The further development turned to resolve very practical problems, such as monitoring environmental contaminations [6], controlling industrial processes [7, 8], or sorting waste materials [9]. With the first international LIBS conference held in 2000 in Pisa, Italy, the international LIBS community was established with the specific missions to make LIBS a mature technology and to develop its applications. A much larger range of demands in various domains has stimulated the development of the technique. In a non-exhaustive list, we can cite analysis of art works and cultural heritages for their conservation [10]; detection and analysis of bacteria [11, 12] and explosives [13, 14] for the needs from national security and homeland defence; direct analysis of trace metallic elements in fresh vegetables [15]; geological studies [16]; application in the nuclear industry [17]; and finally the space exploration with the integration by the NASA of the LIBS module, ChemCam, in Curiosity rover for the analysis of the soil on the Mars [18, 19]. The widespread and rapid development of LIBS applications contrasts however with its actual status of “between science and mature technology” [5]. Such contrast can be considered in parallel with that existing between the conceptual simplicity of the LIBS technique and the complexity of the physical processes involved in laser ablation and in expansion of the produced plasma into ambient gas. The requirement of a quantitative analysis with high performance is actually the major challenge faced by the international LIBS community to mature the technique. Back to the fundamental in order to reach a deeper understanding of the laser-induced plasma is considered today