Mars Analysis by Laser-Induced Breakdown Spectroscopy (MALIS): Influence of Mars Atmosphere on Plasma Emission and Study of Factors Influencing Plasma Emission with the Use of Doehlert Designs

Abstract

A project called MALIS (Mars Analysis by Laser-Induced breakdown Spectroscopy) is under progress to perform in situ analysis of Mars soils and rocks. This paper reports on the behavior of plasma in Martian conditions, i.e., in a CO₂ atmosphere at pressures between 5 and 12 mbar. Plasma expansion and lifetime have been studied in order to compare plasma evolution under standard conditions (air at atmospheric pressure) and in a Mars atmosphere. We have shown that the Mars environment favors plasma expansion and lifetime. The second part of the study concerns optimization of the emission signal from the plasma. An original approach has been chosen, as we used a Doehlert design for the first time in laser-induced breakdown spectroscopy (LIBS). The best conditions obtained are for a laser wavelength of 1064 nm with the maximum energy available due to space limitations, which is 40 mJ at 15 Hz. The other factors studied are delay, angle of incidence, and CO₂ pressure. We have shown that these factors do not have the same influence depending on which spectroscopic line is used, i.e., the atomic line or the ionic line.