VIRTUAL Thursday, December 17th , 2020 3:45 – 4:45 p.m. WEBEX Speaker: Erin Dauson EES-17: Geophysics- Los Alamos National Laboratory “Acoustic signals from laser-induced breakdown spectroscopy: Listening for coatings on martian rocks” Abstract: Rock coatings can provide information about the rock’s history of interactions with water, the atmosphere, or life, providing additional information about martian climate, habitability, and potential biosignatures; thus they are important targets to identify for study by the Mars 2020 SuperCam instrument. SuperCam includes a laser-induced breakdown spectroscopy (LIBS) instrument to examine rock composition and a microphone to record the sound of LIBS analyses. As LIBS penetrates thin coatings through a series of laser shots, coatings may be discernible in the returned spectral data if the composition of the coating and rock differ. However, for rock coatings with a similar composition to the substrate, LIBS spectral data alone may not show a clear change. The LIBS acoustic signal provides a complementary method to examine rock coatings. Previous work noted acoustic amplitude changes as LIBS penetrated coatings on substrates. In this talk we will present acoustic results from LIBS analyses on various coated materials in a thermal vacuum chamber at martian temperatures, pressures, and atmospheric composition, with a 1.5m sample to microphone standoff distance, over a range of laser energies. The experimental setup included an EK series Knowles microphone, which matches the microphone on SuperCam, and a 1/8” Brüel and Kjær (B&K) microphone, selected for its broadband, large, dynamic range. The B&K microphone was digitized with trigger signal based on the laser pulse time. There is a discernible difference in LIBS acoustic signature when targeting a steel substrate compared to a steel substrate coated with copper. In addition to changes in acoustic amplitude with ablation through a copper coating, our results also showed a change in acoustic pulse time of arrival. The pulse time of arrival is correlated with pulse amplitude. This indicates nonlinearity, and may provide information about shockwave formation from LIBS. Preliminary data on natural samples, like marble, show more complex acoustic signatures, but also show a relationship between acoustic amplitude and acoustic arrival time. Upcoming experiments on natural rock samples will provide additional clarity about the types of acoustic signals that may be of interest on Mars.