Experimental Design For Remote Laser Evaporative Molecular Absorption Spectroscopy Sensor System Concept

Surface material on a remote target can be characterized by using a spectrometer to view a laser-heated spot on the target surface through the plume of ejected material. The concept is described as Remote Laser Evaporative Molecular Absorption (R-LEMA) spectroscopy.(1,2) The proposed method is distinct from current stand-off approaches to composition analysis, such as Laser-Induced Breakdown Spectroscopy (LIBS), which atomizes and ionizes target material and observes emission spectra to determine bulk atomic composition. Initial simulations of R-LEMA absorption profiles based on theoretical models show great promise for the proposed method. This paper describes an experimental setup being developed to acquire R-LEMA spectra in the laboratory under controlled conditions that will allow comparison to theoretically predicted spectral profiles. A sample is placed in a vacuum space; a laser beam is directed at the sample, through an optical window. As the sample is heated, and evaporation begins, thermal emission from the heated spot passes through the molecular plume, then out of the vacuum space via infrared windows. The thermal emission is directed into a FT-IR spectrometer, which is equipped with a source-brightness comparator to correct for changes in source intensity during a scan. Targets of known composition are tested and laboratory measurements are compared to the theoretically predicted spectra. Laboratory spectra for composite targets are also presented, including terrestrial rocks and asteroid regolith simulant.