Raman Spectroscopy Laser Damage Quantification in Carbonaceous Chondrite meteorites and its effects on Carbon species present.

Abstract:

Raman spectroscopy and microRaman spectroscopy are commonly utilized to analyze both terrestrial and extraterrestrial materials. However, many extraterrestrial materials, such as carbonaceous chondritic meteorites, have very low albedos, which indicates that the majority of light is absorbed by the material, causing considerable heating of the material due to the laser utilized in Raman, even when very low laser powers are used. Several authors in the fields of Meteoritics, Geology, Chemistry, and Paleontology have urged the importance of utilizing laser powers of less than 0.4 mW to minimize damaging carbonaceous samples. Here, we report damage from laser's powers as low as 0.15 mW (0.1 percent) when using a 20X magnifying objective. This can be problematic, as typical Raman instrument's lowest power settings are thus able to damage the sample, at the very least by heating the sample and changing the thermometry. Raman thermometers are assumed to be highly reproducible and non destructive, making them more advantageous for measurements of small samples. We also present a theory on the chemical mechanisms of the damage, the destruction of weak bonds in the Kerogen-like organics and the subsequent freeing of small, volatile organics from the matrix, which may be removed over multiple irradiations. This creation and excitation of Poly-Cyclic Aromatic Hydrocarbons(PAHs) can have grave health effects for any laboratory performing Raman studies freely, as PAHS are highly carcinogenic.