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

Abstract

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.

Acoustic monitoring of laser-induced phase transitions in minerals: implication for Mars exploration with SuperCam

“…To do this, iron oxides were selected to test this hypothesis: hematite ( ), magnetite ( ) and goethite (FeO(OH)), owing to their relevance for the exploration of the surface of Mars 13 , 14 . Moreover, a laser-induced phase transition was previously observed for hematite 11 , 12 . In addition, a natural diamond and graphite were also selected for their specific physical properties: low (transparency) versus high (opacity) optical absorption of the LIBS infrared laser beam respectively, and extreme hardness for diamond.…”

“…Irradiance deposited on the target ( over a diameter spot for SuperCam) creates an ablation crater, up to few hundreds micrometers deep for a 30 shot burst 8 . It may also alter locally the mineralogical structure within this laser-induced crater 11 , 12 . For example, some high optical absorption minerals have been shown to exhibit laser-induced mineral phase transitions due to melting followed by recrystallization (hematite is transformed to magnetite for instance) or amorphization (graphite into amorphous carbon) within the LIBS crater 11 .…”

Detecting sulfur on the Moon: The potential of vacuum ultraviolet laser-induced breakdown spectroscopy

“…This should be kept in mind when establishing LIBS calibration curves or estimating detection limits from the data. The area probed with the Raman spectrometer is, however, not the same as the area probed with the VUV-LIBS system, because the LIBS system does not allow precise targeting of particular locations in its current configuration, and for post-LIBS Raman spectroscopy measurements, the sample may have been altered by the LIBS pulse and produce unrepresentative results [79,90,91].…”

GeoRaman

“…Laser-induced breakdown spectroscopy (LIBS) is often coupled to Raman spectroscopy in the planetary investigations as they will be present together in next Mars rovers. Schröder et al [22] investigate the effects of different conditions, simulating Mars environment, on LIBS and Raman measurements of Fe, Ni, Ti and their oxides. Rammelkamp et al [23] shown that the low-level fusion of Raman and LIBS data is helpful in the multivariate analysis of Mars-relevant salts such as sulfates and their mixtures as well as carbonates, chlorides and perchlorates.…”