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Humboldt-Universität zu Berlin - Faculty of Mathematics and Natural Sciences - Optical Systems

Humboldt-Universität zu Berlin | Faculty of Mathematics and Natural Sciences | Department of Physics | Optical Systems | Publications | Effects of pulsed laser and plasma interaction on Fe, Ni, Ti, and their oxides for LIBS Raman analysis in extraterrestrial environments

Susanne Schröder, Kristin Rammelkamp, Franziska Hanke, Iris Weber, David S Vogt, Sven Frohmann, Simon Kubitza, Ute Böttger, and Heinz‐Wilhelm Hübers (2019)

Effects of pulsed laser and plasma interaction on Fe, Ni, Ti, and their oxides for LIBS Raman analysis in extraterrestrial environments

Journal of Raman Spectroscopy.

Laser‐induced breakdown spectroscopy (LIBS) and Raman spectroscopy have a high potential for in situ geochemical and mineralogical analyses for planetary exploration, in particular in combination. The SuperCam instrument onboard NASA's Mars 2020 rover will use both techniques together on another planet for the first time. The high‐power pulsed LIBS laser ablates material, and a small luminous plasma is produced for spectral analysis. The laser–matter interaction and the plasma shock wave can alter the sample surface, and new molecules can be produced, which deposit close to the LIBS ablation crater. Subsequent Raman analysis might then not sample the original structure. Here, we investigated pure metals (Fe, Ni, and Ti), the iron‐containing oxides hematite and ilmenite, and a fragment of the Gibeon meteorite in terrestrial ambient conditions, in simulated Martian atmospheric conditions, and in vacuum. LIBS ablation craters and their close proximity were studied with subsequent Raman analysis. Our analysis shows that Earth and Mars atmosphere provide enough oxygen in the LIBS plasma to produce oxides with metals from the sample. These can then be observed in the Raman data. Also, carbon was seen in some of the Raman data from the sample after the LIBS measurement. On hematite, a reduction of the mineral, that is, the presence of magnetite, was observed inside the LIBS crater for terrestrial and Martian atmospheric conditions and in vacuum. For the analysis and correct interpretation of Raman data it is important to be aware that alteration could have occurred by a preceding LIBS measurement. Raman analysis of several positions close to the LIBS ablation crater can help to infer the original and a possibly altered structure.

LIBS, Mars, metals and their oxides, Raman spectroscopy, simulated planetary conditions/environments, space missions