Plasma-induced luminescence spectroscopy in Martian atmospheric conditions

Overview & Synopsis

The SuperCam instrument, aboard NASA's Perseverance rover, provides for the first time the hardware capability for time-resolved spectroscopy on Mars. As a consequence, in addition to the atomic and molecular emissions routinely recorded by SuperCam LIBS, plasma-induced luminescence (PIL) features could theoretically also be observed, within the sample, potentially improving the detection capabilities for some minor elements, compared to LIBS. PIL has been studied in terrestrial conditions but not yet examined under Martian atmospheric conditions. Since atmospheric conditions have previously been shown to strongly affect plasma emissions, they may also have a significant influence on PIL. This study aims at assessing the feasibility of PIL spectroscopy in Martian atmospheric conditions. To do so, we investigate the influence of atmospheric pressure and composition on PIL emissions, compared to plasma emissions. We demonstrate that PIL emission can be observed in simulated Martian conditions, despite its lower intensity compared to terrestrial conditions. Moreover, PIL features exhibiting millisecond-range decay have been observed once plasma emissions have decreased significantly; with our experimental conditions, it is achieved with a temporal delay of 200 μs after plasma initiation and a gate of 20 ms. Shorter-lived PIL features have not been observed, possibly due to spectral interference with plasma emissions.