Short-pulse LIBS: fundamentals and applications

Abstract

Introduction The basis of laser-induced breakdown spectroscopy (LIBS) is well established – real time, simultaneous multielement chemical analysis without sample preparation. Although the advantages are well recognized, understanding the fundamental laser ablation processes underlying this technology remains a quest. The heart of LIBS is the luminous plasma; its initiation and history are critical to applications. The plasmas' properties depend on experimental parameters, including the laser pulse (energy, duration, repetition rate, and wavelength), the sample (physical and optical), and ambient atmosphere (gas, pressure). Except for a few research papers in the analytical literature, most LIBS applications are based on nanosecond pulsed lasers. There are two compelling reasons to delve into the short-pulse regime for LIBS – expected differences in the laser–material and the laser–plasma interactions. Stated differently, there is reason to believe that improved analytical accuracy, precision, and sensitivity can be achieved by the use of short-pulsed lasers for LIBS applications. In the LIBS plasma, spectral emission intensity of elemental lines is based on the amount of mass ablated as well as on the concentration of that mass in the sample (ignoring plasma temperature and electron number density for the moment). For accurate chemical analysis, the chemistry of the ablated mass must be representative of the sample (no fractionation). Ideally, there also would be matrix independence; the same amount of mass would be ablated independent of sample properties. These two goals can be realized by better understanding and controlling the laser–material interaction. Finally, the plasma itself can influence the ablation process.