Recording laser-induced sparks on Mars with the SuperCam microphone

https://doi.org/10.1016/j.sab.2020.106000Get rights and content

Highlights

  • LIBS under Mars atmosphere is studied acoustically with a SuperCam microphone

  • LIBS acoustic signal is sensitive to CO2 pressure, laser focus and target distance

  • Microphone data will document SuperCam target by inferring their hardness

  • Volume of a LIBS cavity can be estimated with the decrease of the acoustic energy

Abstract

The SuperCam instrument suite onboard the Mars 2020 Perseverance rover includes a microphone used to complement Laser-Induced Breakdown Spectroscopy investigations of the surface of Mars. The potential of the SuperCam microphone has already been demonstrated for laser ablation under Earth atmosphere in our preliminary study with a small set of samples and fixed experimental conditions. This new experimental study, conducted under Mars atmosphere, explores all the main environmental, instrumental and target dependent parameters that likely govern the laser-induced acoustic signal that will be generated on Mars. As SuperCam will observe targets at various distances from the rover, under an atmospheric pressure that follows diurnal and seasonal cycles, this study proposes a sequence of corrections to apply to Mars data in order to compare acoustic signal from targets sampled under different configurations.

In addition, 17 samples, including pure metals but also rocks and minerals relevant to Mars' surface were tested to study the influence of target properties and laser-matter interactions on the acoustic signal and the ablated volume. A specific behavior is reported for metals and graphite, which rapidly disperse the incoming laser energy through heat diffusion. However, for other minerals and rocks, the growth of the crater is seen to be responsible for the shot-to-shot decrease in acoustic energy. As a consequence, it is confirmed that monitoring the acoustic energy during a burst of laser shots could be used to estimate the laser-induced cavity volume. Moreover, the amount of matter removed by the laser is all the more important when the target is soft. Hence, the decreasing rate of the acoustic energy is correlated with the target hardness. These complementary information will help to better document SuperCam targets.

Introduction

Mars is not as quiet as one can imagine when considering the high sound absorption of the carbon dioxide that composes its low-pressure atmosphere [1]. Indeed, some acoustic waves, especially in the infrasound domain, do propagate and are characteristic of atmospheric phenomena such as dust-devil-like convective vortices [2] or baroclinic waves [3], as detected by the InSight mission. For outreach purposes, pressure variations detected by the InSight Auxiliary Payload Sensor Suite and vibrations captured by the short period seismometer were transposed in the audible. Unfortunately, no real sound recording in the audible range from 20 Hz to 20 kHz has been performed yet.

Scheduled for landing in Jezero crater in February 2021, the Mars2020 Perseverance rover will carry two microphones: one to capture acoustic signals during the entry, descent and landing of the vehicle [4] and the other one, part of the SuperCam instrument suite [5, 6], is designed to operate during surface mission, in combination with the SuperCam Laser-Induced Breakdown Spectroscopy (LIBS) technique. This study focuses on the latter which is located on top the rover mast and co-aligned with the LIBS telescope boresight. It will record laser-induced sparks in the 100 Hz to 10 kHz frequency range, during LIBS analysis, with a sampling rate of 25 kHz or 100 kHz. The microphone's primary objective is to support SuperCam's LIBS investigation, but it will also contribute to atmospheric science: it will monitor wind-induced signals to estimate wind speed and direction [7] and it will infer air temperature through the speed of sound when determining the arrival time of the LIBS sound wave [8]. In addition, it will provide diagnosis information on the operation of companion payloads such as MOXIE or the rover's drill.

The intensity of a laser-induced acoustic signal was experimentally shown to be an indicator of the ablation process (see [9] for a detailed review of the experimental applications of shock-waves in laser-induced plasma). More specifically, after firing 10,000 shots on aluminum-oxide ceramics, Grad and Možina [10] noticed a decreasing shot-to-shot evolution of the acoustic signal with different regimes as a function of the number of shots, attributed to different phases of the ablation crater development, whose transitions depend on the target composition. Moreover, the target that had the lowest ablated volume corresponded to the target that had the smallest difference of the acoustic signal amplitude between the first and the last shots. Similar regimes of the acoustic energy along a depth profile have been observed under Mars atmosphere [11], but the link with the ablated volume was missing.

Our previous experimental study, conducted at Earth pressure and atmospheric composition (Chide et al. [12]), related the laser-induced acoustic signal with laser-induced crater volume and LIBS optical spectrum intensity. For a small set of eight samples, the acoustic energy was shown to decrease with a rate that is dependent on the hardness of the target. For softer targets, the sharp decrease of the acoustic energy was linked with the rapid growth of the laser-induced crater whereas for harder targets, the almost constant acoustic energy corresponded to a low ablation rate. Additionally, a singular behavior of the acoustic energy was observed on the iron‑nickel target which had a constant acoustic energy but a low hardness. Correlating the acoustic energy and the ablated volume together has highlighted a linear relationship between these two quantities: by monitoring the relative acoustic energy between the first and the last shots of a laser burst, it is possible to estimate the ablated volume after this given number of shots. These two results represent valuable information in the context of the in situ exploration of the surface of Mars with SuperCam for instance to characterize rock coatings [13]. Therefore, it is an expected and necessary step to extend this study to Mars atmosphere (low pressure, CO2 composition) as the properties of the background medium influence both the laser-induced plasma parameters and the acoustic wave propagation. Moreover, this present work uses a larger set of samples including metallic targets important for understanding the physical mechanisms generating the acoustic signal and with mineral phases expected to be found on Mars in Jezero crater.

In contrast to laboratory experiments where each parameter can be changed independently of the others, once on Mars, many instrumental and environmental parameters will change from one target to another. Thus, in order to precisely understand the acoustic signal recorded for several targets of different natures, it is a prerequisite to characterize all the parameters that influence the acoustic signal and estimate their sensitivity. Section 2 details a literature review of these parameters that can be grouped into three categories: instrumental, environmental and target-dependent. After a description, in Section 3, of the setup used in this study, Sections 4 and 5 present the behaviors of the acoustic signal when changing experimental conditions and target nature. Finally, Section 6 summarizes the information on the SuperCam Microphone to support LIBS investigation on Mars, and how the acoustic energy can be used to estimate the target hardness and the ablated volume.

Section snippets

Generation of the laser-induced spark

As a laser beam illuminates a sample, its initial energy is converted into heat and transferred within the material. Above a certain threshold energy, ablation of the material occurs: the surface suffers a sudden and sharp increase in temperature leading to a sample mass removal due to vaporization. This vapor is ionized and forms a plasma plume whose pressure is significantly higher than the background pressure leading to the formation of a strong shock wave. The whole process is very complex

A Martian LIBS setup combined with acoustics measurements

The Mars-atmosphere LIBS calibration test bench at Institut de Recherche en Astrophysique et Planétologie (IRAP, Toulouse, France) used the LIBS capability of the ChemCam Mast Unit Engineering and Qualification Model (infrared laser pulse at 1067 nm of about 10 mJ). The Mast Unit was coupled with the ChemCam Body Unit Engineering Model that includes three spectrometers collecting the light emitted from the plasma over the UV (240.1 nm to 342.2 nm), the violet (382.1 nm to 469.3 nm) and the

Influence of experimental parameters

Experimental conditions when using LIBS on Mars are always changing depending on the properties of the selected target, and also on the local climate that controls the daily and seasonal cycles of the atmospheric pressure. On the one hand, the irradiance deposited on the target is the key instrumental parameter that governs the efficiency of the ablation. For both SuperCam and ChemCam, the irradiance depends on the offset between the distance retrieved by the autofocus algorithm and the real

Influence of target properties

This section compares the recorded acoustic energy and the measured ablated volume for all the targets presented in Table 2, which were sampled under a simulated Mars atmosphere.

The acoustics as a support to LIBS investigations on Mars

The combined study of the acoustic energy and the ablated volume has shown that the decrease of the former is a tracer of the ablated volume: the softer the target, the higher the ablated volume and the faster the decrease of the acoustic energy. Hence, tracking the acoustic energy along a LIBS burst can give information about both the target hardness and the ablated volume.

Conclusion

Listening to laser-induced sparks produced under Earth atmosphere has shown to provide useful information on target hardness and ablated volume [12]. In an refinement of this work and in preparation for the SuperCam LIBS investigation on Mars, the acoustic signal from the expansion of the laser plasma on metals, minerals, and rocks, was studied under controlled Mars conditions (carbon dioxide atmosphere and low pressure).

The sensitivity of the acoustic signal with respect to environmental and

Declaration of Competing Interest

None.

Acknowledgments

This work was funded by CNES and Région Occitanie as part of a PhD thesis. We gratefully acknowledge Guy Perez and Romain Petre Bordenave from CNES for their availability with the 3D-surface profiler. Thanks are due to Jean-Claude Boulliard and the Collection de Minéraux (Sorbonne Université, Paris) for providing mineral samples. The NASA Mars Exploration Program supported some parts (ChemCam body unit, RCW participation).

Declaration of interests

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

CRediT authorship contribution statement.

Baptiste Chide: Writing – Original Draft, Conceptualization, Methodology, Formal Analysis, Investigation, Data Curation, Writing – Review & Editing, Visualization. Sylvestre Maurice: Conceptualization, Methodology, Validation, Writing – Review & Editing, Supervision. Agnès Cousin:

References (76)

  • W. Rapin et al.

    Hydration state of calcium sulfates in gale crater, mars: identification of bassanite veins

    Earth Planet. Sci. Lett.

    (2016)
  • K. Horai et al.

    Thermal conductivity of rock-forming minerals

    Earth Planet. Sci. Lett.

    (1969)
  • S. Le Mouélic et al.

    The ChemCam remote micro-imager at gale crater: review of the first year of operations on mars

    Icarus

    (2015)
  • Y. Lu et al.

    Acoustic wave monitoring of cleaning and ablation during excimer laser interaction with copper surfaces

    Appl. Surf. Sci.

    (1997)
  • A. Hrdlička et al.

    Correlation of acoustic and optical emission signals produced at 1064 and 532 nm laser-induced breakdown spectroscopy (LIBS) of glazed wall tiles

    Spectrochim. Acta B At. Spectrosc.

    (2009)
  • Y. Iida

    Effects of atmosphere on laser vaporization and excitation processes of solid samples

    Spectrochim. Acta B At. Spectrosc.

    (1990)
  • Z. Abdel-Salam et al.

    Estimation of calcified tissues hardness via calcium and magnesium ionic to atomic line intensity ratio in laser induced breakdown spectra

    Spectrochim. Acta B At. Spectrosc.

    (2007)
  • J.-P. Williams

    Acoustic environment of the martian surface

    Journal of Geophysical Research: Planets

    (2001)
  • W. B. Banerdt, S. E. Smrekar, D. Banfield, D. Giardini, M. Golombek, C. L. Johnson, P. Lognonné, A. Spiga, T. Spohn, C....
  • L. Martire et al.

    Martian Infrasound: Numerical Modeling and Analysis of InSight’s Data

    (2020)
  • J. Maki, D. Gruel, C. McKinney, M. Ravine, The ECAM team, the mars 2020 engineering cameras and microphone on the...
  • S. Maurice, R.C. Wiens, P. Bernardi, P. Cais, S. Robinson, A. Nelson, O. Gasnault, J.-M. Reess, M. Deleuze, F. Rull,...
  • R.C. Wiens, S. Maurice, S. Robinson, A. E. Nelson, P. Cais, P. Bernardi, R. Newell, S. Clegg, S. Sharma, S. Storms, J....
  • B. Chide et al.

    Experimental wind characterization with the SuperCam microphone under a simulated martian atmosphere

    Icarus

    (2020)
  • B. Chide et al.

    Speed of Sound Measurements on Mars and its Implications, in: 51st Lunar and Planetary Science Conference

    (2020)
  • B. Campanella et al.

    Shock waves in laser-induced plasmas

    Atoms

    (2019)
  • N. L. Lanza, A. M. Ollila, A. Cousin, R. C. Wiens, S. Clegg, N. Mangold, N. Bridges, D. Cooper, M. Schmidt, J. Berger,...
  • J.M. Vadillo et al.

    Effect of plasma shielding on laser ablation rate of pure metals at reduced pressure

    Surf. Interface Anal.

    (1999)
  • E. Manikanta et al.

    Effect of pulse duration on the acoustic frequency emissions during the laser-induced breakdown of atmospheric air

    Appl. Opt.

    (2016)
  • E. Manikanta et al.

    Effect of laser intensity on temporal and spectral features of laser generated acoustic shock waves: ns versus ps laser pulses

    Appl. Opt.

    (2017)
  • X. Zeng et al.

    Laser–plasma interactions in fused silica cavities

    J. Appl. Phys.

    (2004)
  • C. Porneala et al.

    Observation of nanosecond laser-induced phase explosion in aluminum

    Appl. Phys. Lett.

    (2006)
  • D.A. Cremers et al.

    Laser-Induced Breakdown Spectroscopy

    (2012)
  • C.T. Walters et al.

    Transient reflectivity behavior of pure aluminum at 10.6 microns

    Appl. Phys. Lett.

    (1978)
  • G. Taylor, The formation of a blast wave by a very intense explosion i. theoretical discussion, Proceedings of the...
  • Y. Zel’dovich et al.

    Physics of Shock Waves and High-Temperature Hydrodynamic Phenomena

    (1967)
  • S.S. Harilal et al.

    Experimental and computational study of complex shockwave dynamics in laser ablation plumes in argon atmosphere

    Physics of Plasmas

    (2012)
  • H. E. Bass, L. C. Sutherland, J. Piercy, L. Evans, Absorption of sound by the atmosphere, in: Physical acoustics:...
  • Cited by (26)

    • Measurements of sound propagation in Mars' lower atmosphere

      2023, Earth and Planetary Science Letters
    • Generation and evolution of laser-induced shock waves under Martian atmospheric conditions

      2023, Icarus
      Citation Excerpt :

      This bandwidth limit also limits the risetime of the signal in the time-domain (Chide et al., 2019; Yuldashev et al., 2008). The initial compression phase is typically used to trace the acoustic energy of the pressure wave (Chide et al., 2020; Chide et al., 2019; Grad and Možina, 1993). Its duration, measured as the HWHM, is about 22 μs, which corresponds to a width of about 6 mm.

    • Differentiation of closely related mineral phases in Mars atmosphere using frequency domain laser-induced plasma acoustics

      2022, Analytica Chimica Acta
      Citation Excerpt :

      The laser-induced plasma evolution radically changes under low-pressure conditions and atmosphere composition. Previous studies have highlighted benefits derived from using LIBS and acoustic data either by data fusion [13] or in correlation [11,12] under Earth and Mars-like environment, yet frequency spectra remain to be tested for similar purposes. Lastly, the capability of LIBS and the recorded frequencies for sample classification was tested independently to expand on the reported results.

    • Correlation of characteristic signals of laser-induced plasmas

      2022, Spectrochimica Acta - Part B Atomic Spectroscopy
      Citation Excerpt :

      It has been shown that there is a relation between the amount of ablated material and amplitude of the sound signal [32,33]. The amplitude is dependent on several experimental conditions, where the highest signal is acquired when the laser is at the best focus [34] or with the increasing laser energy [35]. The amplitude of the sound may be also used in combination with the LIBS spectra [36], where a relation between the LIBS spectra and the sound amplitude has been observed [34].

    View all citing articles on Scopus
    View full text