Femtosecond Laser-Induced Breakdown Spectroscopy: Physics, Applications, and Perspectives

Abstract

Progress in technology and society continually places new demands on analytical science and more powerful and informative methods need to be developed. One among them is laser-induced breakdown spectroscopy (LIBS), sometimes also referred to as LIPS (laserinduced plasma spectroscopy). Typically, LIBS measurements are conducted with nanosecond time scale lasers. A review by Song et al.1 and two recently published books by Miziolek et al.2 and Cremers et al.3 give a good overview of instrumental developments in this area. However, new developments in laser technology have made ultra-short lasers available4 and have stimulated an interest in LIBS with ultra-short pulses. There are fundamental differences between the ablation processes of ultra-short ( 1 ps) and short ( 1 ps) pulses that result in different mechanisms of energy dissipation in the sample. In the case of ultra-short laser pulses, at the end of the laser pulse, only a very hot electron gas and a practically undisturbed lattice are found, which subsequently interact. However, for longer pulses above a certain energy threshold, the material undergoes transient changes in the thermodynamic states from solid, through liquid, into a plasma state.5,6 Based on this difference, consequences for the analytical performance of the method can be expected that in the future should lead to new aspects in instrumentation and applications of LIBS. The goal of this review is to summarize current knowledge of the instrumentation and physics of laser ablation with femtosecond lasers and to draw some conclusions concerning new possible applications that rely on these specific new features. It seems clear that even if a better performance in terms of analytical figures of merit compared to standard LIBS applications7 is found, a replacement of current technology cannot be expected soon due to the cost and complexity of chirped pulse amplification (CPA) laser systems. However, current trends in other fields of application of these laser systems, e.g., medical laser applications or material processing,8 may change this picture in the near future.