Acquisition of a Multi-Parameter LIBS Reference Database of Geological Materials-PSI

Laser-induced breakdown spectroscopy has become an important tool used to answer key science questions on existing and planned missions (MSL Curiosity and Mars 2020, respectively). However, the accuracy of these LIBS-derived measurements is plagued by matrix effects and a dearth of calibration information. The goal of this proposal is to create a database of LIBS spectra collected under a range of conditions anticipated during deployments to remote locations on Mars, the lunar surface, asteroids, and Earth. This spectral library would allow future researchers to search the database for spectra that match their experimental conditions and generate optimal calibrations for a variety of LIBS deployments.
Three key objectives are employed to facilitate the collection of a universal LIBS spectral library and optimize elemental predictions on remote surfaces:
1. Acquire LIBS spectra at variable plasma temperatures to replicate spectra collected by different instruments and at a range of standoff distances,
2. Acquire LIBS spectra under multiple atmospheres and pressures germane to potential LIBS-based exploration, and
3. Create multivariate calibrations capable of providing reliable elemental predictions for LIBS spectra collected on future missions. The Mineral Spectroscopy Laboratory at Mount Holyoke College (MHC) is in a unique position to meet these objectives. A calibration
suite of nearly 3,000 rock powder standards was collected from several sources with support from the Mars Fundamental Research program and is currently housed at MHC. In addition, the SuperLIBS instrument at MHC has a sensitivity and resolution throughout the UV, VIS, and VIS-NIR regions that are equal or superior to the SuperCam LIBS instrument on the Mars 2020 rover. SuperLIBS is designed for rapid collection of thousands of spectra at multiple laser energies on up to one hundred targets in a single day. This instrument provides calibration data that match or exceed the resolution of spectra collected during any anticipated deployments on Earth or other remote surfaces.
Objectives one and two will be met by collecting spectra at three laser energies that produce the range in plasma temperatures that
are anticipated on future missions. This will be repeated under a Mars-analog atmosphere, vacuum, and ambient (Earth) conditions. Due to the high sample throughput capabilities of SuperLIBS, all ~3000 calibration standards can be run under three atmospheres
at multiple laser energies in a timeframe suitable for this solicitation. Objective three will be met by posting spectra to the DEVAS website (nemo.mtholyoke.edu/) built and maintained by MHC and then (annually) to PDS. Capabilities of DEVAS include wavelength resampling and masking, baseline removal, and normalization; all before generating multivariate calibration models for major, minor, and trace elements.
Current practice in quantitative LIBS is to develop a calibration suite optimized for a single experiment. Due to time and funding constraints, such calibration suites are typically orders of magnitude smaller than what we are proposing, and often only include only a limited number of standards. This proposal would eliminate the need for individual research groups to analyze their own calibration suites, and instead allow them to select relevant spectra from our immense spectral library. This approach will conserve valuable resources such as time and funding by providing key calibration support for experiments conducted under a variety of conditions.