The application of Laser Induced Breakdown Spectroscopy (LIBS) to the analysis of geological samples in simulated extra-terrestrial atmospheric environments

Laser induced breakdown spectroscopy (LIBS) is a technique that can determine the elemental composition and quantities of a sample by the spectral analysis of a laser induced plume. This study was undertaken to develop, characterise and assess the use of the LIBS technique on geological samples in different pressure and gaseous environments. The experimental range chosen was dictated by the planetary conditions on Titan and other extra-terrestrial bodies with the samples analysed chosen to complement a range of rock types. A LIBS system was developed, together with associated experimental apparatus able to acquire results in varying pressure and gaseous environments. The capability of LIBS to analyse weathered rock samples was investigated under various ambient conditions; pressures of 160x103 Pa to 0.4x10-3 Pa and ambient gaseous mixtures of air, nitrogen and methane. Particular attention was paid to temporal and power considerations under such regimes. As was expected, the chosen delay time to optimise the emission signals needed to be increased with increasing ambient pressure. At power values as low as 28.5 mJ/pulse (using a 6 ns pulse from a doubled Nd:YAG laser at 532 nm) a valid emission signal could be obtained. Increasing the laser power resulted in a reduction in the overall signal to noise ratio. It was observed that ambient methane quenches the optical emission signal due to non-radiative transitions. In spite of this, valid qualitative data are obtainable, even when emissions due to carbon transitions from both the sample and the gaseous environment, are present. Results are presented which support the premise that the LIBS technique can be used to investigate both the surface and depth compositions of geological samples under extra-terrestrial conditions