Elemental Abundance Measurement Using Micro-libs for Space Exploration

Introduction: As LIBS has been applied to a wider and more useful range of samples, it has been realized that signals generated with the laser plasma are highly dependent upon the matrix from which they have been ablated. In this case, analytical results dependence on physical properties of the sample. This at times leads to the paradoxical situation where precisely matrix matched calibration standards are required to analyze an unknown sample. While several strategies for solving the calibration problems of LIBS have been proposed, none so far is generally applicable to geological samples, especially to extraterrestrial analysis, in which foreknowledge of the sample composition is particularly challenging. Micro-LIBS: Standoff LIBS has been developed for space applications [1,2], and is part of the 2009 Mars Science Laboratory (MSL) payload. Micro-LIBS is Laser Induced Breakdown Spectroscopy (LIBS) applied for interrogation of surfaces at <50 μm interrogation diameter and with <1 mJ of laser pulse energy. A μLIBS instrument could be used to produce elemental abundance maps of mineralogical surfaces near to or at the grain size of the sample. Analysis Appraoch: We are devopling a data analysis technique which uses multiple emission lines per element. By using the extra degrees of freedom associated with observations on the multiple emission lines per element and developing the physical constitutive relationships between these emission lines, an observation of the time-integrated thermal profile (spatial and temporal) of the high temperature gas that drives emission can be solved in conjunction with the relative elemental abundances. In mathematical form, the ionized gas/plasma state matrix (temporal and spatial), P, describing the thermal evolution of the ionized gas from which emission is occurring is solved simultaneously with the relative elemental abundances in the gas, C m , using known elemental partition functions, Z m , for the elements, m, and the vector of observed elemental lines of emission, Fobs m . As shown in [3] these relationships should collectively minimize the following least squares function: