Acoustic monitoring of laser-induced phase transitions in minerals - implication for Mars exploration with SuperCam
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2021-12-15 |
| Journal | Scientific Reports |
| Authors | Baptiste Chide, Olivier Beyssac, M. Gauthier, Karim Benzerara, Imène Esteve |
| Institutions | UniversitĂŠ Toulouse III - Paul Sabatier, Institut de minĂŠralogie, de physique des matĂŠriaux et de cosmochimie |
| Citations | 15 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive Summaryâ- Core Achievement: The study successfully demonstrated that laser-induced mineral phase transitions (e.g., hematite to magnetite) can be remotely monitored and identified using the acoustic signal generated by Laser-Induced Breakdown Spectroscopy (LIBS).
- Acoustic Signature of Transition: A sharp increase in acoustic energy amplitude (approximately 25% for iron oxides, 5x for diamond) was consistently observed over the first 5 LIBS shots for minerals that undergo phase change (hematite, goethite, diamond).
- Mechanism: The acoustic spike is directly linked to the transformation of the target material (e.g., hematite to magnetite or diamond to amorphous carbon), which significantly alters the materialâs physical properties, specifically reducing the optical and thermal penetration depths.
- Material Transformation Confirmed: Post-ablation analysis using Raman spectroscopy and SEM confirmed that hematite and goethite transformed into a molten layer of magnetite, and diamond transformed into amorphous-like carbon within the ablation zone.
- Implication for SuperCam: This behavior, occurring only for specific phases, proves that the SuperCam microphone on the Mars Perseverance rover provides crucial mineralogical discrimination capabilities that complement the limited stoichiometric information available from the LIBS optical spectrum alone (e.g., distinguishing hematite from magnetite).
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Laser Wavelength | 1067 | nm | LIBS system (Infrared pulse) |
| Laser Pulse Duration | 5 | ns | LIBS system pulse length |
| Laser Energy Deposited | ~10 | mJ | ChemCam Mast-Unit EQM |
| Laser Irradiance (Target) | >1 | GWcm-2 | SuperCam operational irradiance |
| Ablation Spot Diameter | ~300 | Âľm | SuperCam ablation spot size |
| Simulated Mars Pressure | 6 | mbar | Martian chamber environment |
| Simulated Mars Atmosphere | 95.7% CO2, 2.7% N2, 1.6% Ar | % | Gas mixture composition |
| Microphone Sampling Rate | 200 | kHz | Acoustic data acquisition |
| Acoustic Energy Increase (Fe Oxides) | ~25 | % | Increase observed over the first 5 shots (Hematite, Goethite) |
| Acoustic Energy Increase (Diamond) | 5 | Factor | Increase observed over the first 5 shots |
| Hematite Thermal Penetration (δth) | 140 | nm | At 1067 nm laser wavelength |
| Magnetite Thermal Penetration (δth) | 92 | nm | At 1067 nm laser wavelength |
| Diamond Optical Penetration (δopt) | 1.3 x 107 to 2.2 x 108 | nm | Extremely low absorption (transparent to IR laser) |
| Amorphous Carbon Thermal Penetration (δth) | 141 | nm | Isotropic thermal property |
Key Methodologies
Section titled âKey Methodologiesâ-
LIBS Ablation (Mars Simulation):
- Samples (hematite, goethite, magnetite, graphite, diamond) were placed in a vacuum chamber simulating Mars conditions (6 mbar, CO2-rich atmosphere).
- A LIBS system (ChemCam EQM) delivered 10 mJ, 5 ns infrared pulses (1067 nm) at a 3 Hz frequency.
- Bursts of 30 laser shots were performed on each sample, with specific short bursts (1 to 5 shots) used for detailed crater analysis.
-
Acoustic Signal Recording:
- A SuperCam-like Knowles Electret condenser microphone (22.4 mV Pa-1 sensitivity) was positioned to record the shock wave generated by the plasma.
- The acoustic waveform was sampled at 200 kHz.
- Acoustic energy (Pa2s) was calculated as the square value of the acoustic waveform during the compression phase for each shot.
-
Post-Ablation Crater Analysis (SEM):
- Scanning Electron Microscopy (SEM, Zeiss Ultra 55) was used to image the resulting craters, focusing on microtexture, morphology, and the presence of molten or transformed layers.
- SEM confirmed the formation of a smooth, cracked molten-like layer (magnetite) on hematite and an alveolar molten texture on goethite.
-
Phase Identification (Raman Spectroscopy):
- A continuous-wave Raman microspectrometer (Renishaw InVia Reflex, 532 nm laser) was used for high-resolution analysis (~1-2 Âľm).
- Hyperspectral Raman mapping was performed on the craters to determine the percentage of the surface covered by the transformed phase (e.g., magnetite) after 1, 2, 3, and 5 shots.
- Raman spectra confirmed the transition of hematite/goethite to magnetite (664 cm-1 peak) and diamond to amorphous carbon (D-band at 1345 cm-1, G-band at 1600 cm-1).
Commercial Applications
Section titled âCommercial Applicationsâ- Planetary and Deep Space LIBS Systems:
- Enabling enhanced mineralogical identification on missions like Mars 2020, where LIBS optical data alone cannot distinguish between chemically similar phases (e.g., Fe2O3 vs. Fe3O4).
- Using acoustic data to rapidly assess the hydration state of minerals (e.g., detecting dehydration of goethite via hydrogen line decrease and acoustic spike).
- Remote Material Characterization:
- Integrating acoustic monitoring into terrestrial LIBS systems for non-contact, real-time assessment of material physical properties (hardness, optical absorption, thermal diffusivity).
- Quality Control in Manufacturing:
- Monitoring laser-material interaction during laser processing (cutting, welding, ablation) to detect unintended phase changes or structural modifications in materials like carbon allotropes or metal oxides.
- Geological Surveying and Resource Mapping:
- Field-portable LIBS systems equipped with microphones could quickly identify specific mineral phases (e.g., high-value diamond or specific iron ores) based on their unique acoustic response during the initial ablation shots.