Acoustic spectroscopy of laser-induced plasma

Abstract

This dissertation presents a novel strategy for the incorporation of acoustic signals in laser-induced breakdown spectroscopy. In recent years, there has been an increasing focus on the fusion of diverse analytical approaches to enhance qualitative and quantita-tive analyses. A notable approach involves the utilisation of the acoustic signal generated by the laser-matter interaction between the sample and the laser pulse, a technique that has been employed by the Mars 2020 mission rover Perseverance. This dissertation aims to explicate several acoustic-spectroscopic phenomena that establish novel, systematic scientific foundations for the final complementarity of these methods. The initial section is dedicated to the examination of the influence of the physico-chemical properties of the samples on the acoustic and emission signals, with additional consideration of the impact of the positioning of the acoustic receiver, in this case, a commercially available condenser microphone. The subsequent section explores the practical application of this knowledge, with a particular focus on the field of geology, emphasising the domain of chemical acoustic-emission mapping. It has been demonstrated that the acoustic signal provides highly ac-curate and precise distribution maps with respect to the sample composition, comple-menting the chemical maps obtained from emission spectra. In the third part, the focus was on the influence of instrumentation on acoustic-emission signal. The study investigated the influence of the ablation source wavelength and different types of microphones, with a particular emphasis on MEMS microphones (micro-electro-mechanical systems). These microphones are characterised by good com-pactness, robustness, small size and a wide choice according to the required acoustic-mechanical properties. The section was further expanded to consider the acoustic-emission analysis of nano- and microlayers, where the acoustic signal yielded results analogous to those of the emission signal. In the final section, the focus was directed towards the examination of the effects of altering atmospheric conditions, with the primary objective being the imitation of the atmospheric conditions that prevail on Mars. This approach was undertaken to achieve a more accurate approximation of the real conditions in which the Perseverance rover is currently operating. This involves monitoring variations in temperature (-40 to 20°C), ambient gas pressure modifications (1 to 30 mbar CO2) and the composition of the sur-rounding atmosphere (Ar, Air, N2, CO2). The four sections of this dissertation constitute the pioneering systematic acoustic-emission study of its kind, thereby providing invaluable insights for the future application of the LIBS-LIPAc (Laser-Induced Plasma Spectroscopy & Laser-Induced Plasma Acoustic) method in real-world research in harsh and extraterrestrial environments.