Probing organic residues on Martian regolith simulants using a longwave infrared laser-induced breakdown spectroscopy linear array detection system

摘要

Recently, a mercury-cadmium-telluride (MCT) linear array detection system that is capable of rapidly capturing (～1-5 second) a broad spectrum of atomic and molecular laser-induced breakdown spectroscopy (LIBS) emissions in the longwave infrared region (LWIR, ～5.6 to 10 μm) has been developed. Similar to the conventional Ultraviolet (UV)-Visible (Vis) LIBS, a broad band emission spectrum of condensed phase samples covering the entire 5.6 to 10 μm region can be acquired from just a single laser-induced micro-plasma or averaging a few single laser-induced micro-plasmas. This setup has enabled probing samples "as is" without the need for extensive sample preparation and also offers the possibility of a simultaneous UV-Vis and LWIR LIBS measurement. A Martian regolith simulant (JSC Mars-1A) was studied with this novel Vis + LWIR LIBS array system. A broad SiO_2 vibrational emission feature around 9.5 μm and multiple strong emission features between 6.5 to 8 μm can be clearly identified. The 6.5 to 8 μm features are possibly from biological impurities of the simulant. JSC Mars-1A samples with organic methyl salicylate (MeS, wintergreen oil) and Dimethyl methyl-phosphonate (DMMP) residues were also probed using the LWIR LIBS array system. Both molecular spectral signature around 6.5 μm and 9.5 μm of Martian regolith simulant and MeS and DMMP molecular signature emissions, such as Aromatic CC stretching band at 7.5 μm, C-CH_3O asymmetric deformation at 7.6 μm, and P=O stretching band at 7.9 μm, are clearly observed from the LIBS emission spectra in the LWIR region.