The versatility of laser-induced breakdown spectroscopy (LIBS) resulting from its advantageous analytical characteristics is, unfortunately, still limited by challenges inherent to the fundamental principles of the method - the processes of laser ablation and laser-induced plasma generation. Unwanted effects (generally known as matrix effects) significantly decrease the analytical performance of LIBS, complicating quantification and impairing reproducibility. This study investigates acoustic signals accompanying plasmas (LIPAc) to overcome these limitations and enhance LIBS performance. The influence of instrumental (microphone types), operational (laser wavelength and fluence) and sample parameters on acoustic responses were evaluated. The results indicate that laser fluence strongly influences acoustic wave oscillation. When laser fluence substantially exceeds the breakdown thresholds of the different components in the matter, acoustic responses may become identical across various materials. On the other hand, proportionality in differences of acoustic signal is maintained for different microphones and laser wavelength settings. Promising solutions for eliminating matrix effects on various surfaces were identified, but the suitability and efficiency may be highly dependent on the emission line used. This is demonstrated using the signals of atomic Cu(I) 324.74 nm and ionic Cu(II) 329.04 nm lines measured from an aluminum sample with a partially coppered and partially roughened surface. Acoustic maps of a galena ore sample demonstrate the applications of LIPAc in spatially resolved LIBS imaging and elemental mapping. These maps can help eliminate the discrepancy between the intensities of the calcium atomic line of Ca(I) at 422.67 nm measured from the galena mineral and calcium carbonate.

Planetary rover missions on Mars have suffered entrapments and serious mobility incidents due to soil assessment limitations of stereo RGB cameras, which cannot characterize relevant physical phenomena such as thermal behavior that depend on granularity and cohesion. In particular, thermal inertia estimations are already being used to assess geophysical properties from 1-D low-resolution measurements by onboard thermopiles. However, no high-resolution measurements are currently available to characterize Martian soils for safer navigation in future missions, so new experimental methods are required to capture and analyze thermal images with planetary conditions in Earth-based experiments. In this work, we propose a novel measurement system configuration and experimental methodology to capture thermal images using isolated multipurpose environmental chambers (MECs) to replicate the temperature and pressure conditions of Mars. Furthermore, the system has allowed to measure diurnal cycles for four soil types of known physical characteristics under Martian and Earth pressures to perform a unique quantitative analysis and comparison of thermal behavior and thermal inertia for soil assessment. Even if no actual Martian infrared (IR) images are available for comparison, results indicate a correlation between granularity and thermal inertia that is consistent with available thermopile measurements recorded by rover’s onsite. Furthermore, the set of measurements acquired in the experiments has been made available to the scientific community.

Moonmilk-type deposits exemplify carbonated Martian analogues existing in the subsurface of Earth, an endokarstic speleothem with a possible biochemical origin composed principally by carbonates, mainly huntite and dolomite. In this work, samples of moonmilk located in Nerja Cave (southern Spain) have been studied by LIBS with the aim of identifying carbon of biogenic origin by establishing a relationship between a molecular emission indicator, CN signal, and the organic carbon content. The characterization of this kind of carbonate deposit with a multiple mineralogical composition has been completed using scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and X-ray diffraction techniques for qualitative and semi-quantitative analysis. The information attained from LIBS regarding energy thresholds and time-resolved kinetics of CN emissions provides useful insight into the identification of different molecular emitters, namely organic and inorganic CN, depending on the laser irradiance and time settings conditions. These promising results are of application in the search and identification of biosignatures in upcoming planetary missions with astrobiological purposes.

Abstract:The Mars 2020 Perseverance rover, which landed in February 2021, is carrying the SuperCam remote sensing suite [1,2]. It is a multifunctional spectroscopy instrument to analyze Martian rocks and soils with Laser-Induced Breakdown Spectroscopy (LIBS), time resolved Raman and luminescence, Visible and Infrared Reflectance Spectroscopy, and color context imaging. It also includes a microphone (see Fig. 1) that records acoustic pressure fluctuations in the 100 Hz to 10 kHz frequency bandwidth. In particular, it supports LIBS investigation by listening to laser-induced sparks caused by the supersonic expansion of the plasma plume [3, 4]. The microphone also contributes to atmospheric science by recording the ambient noise [wind, turbulence, 5, 6] and it already listened to unique sounds from the Ingenuity Mars Helicopter flights. This abstract focuses on the first analysis of the LIBS acoustic signal recorded on Martian targets near the Octavia E. Butler landing site of Perseverance.Figure 1 - WATSON image of the upper part of the Perseverance Remote Sensing Mast. The microphone is seen in the red rectangle. Credits: NASA/JPL-Caltech/MSSS/ASUListening to laser-induced sparks on Mars:The LIBS experiment of Supercam uses a pulsed laser in the infrared (1064nm) to ablate rock or soil targets at the Mars surface at distance up to 7 meters. A standard LIBS burst consists of 30 laser shots repeated at the same location on a target. It creates an ablation pit up to hundreds of µm deep, depending on the target hardness (see LIBS pits in Fig. 2) [4, 7]. Longer bursts of 150 shots, called depth profiles, can also be performed to look for any chemical stratification with depth.Figure 2 - Hedgehog target (sol 37) sampled by LIBS (10 points of 30 shots each). (a) Mastcam-Z documentation image. (b) RMI context mosaic highlighting the LIBS pits.Credits: NASA/JPL-Caltech/ASU/MSSS and NASA/JPL-Caltech/LANL/CNES/IRAPIt has been shown in lab studies [3, 4] that recording of the LIBS acoustic signal helps to determine the target physical properties (hardness) and also the laser pit volume by looking at the decrease of the signal amplitude with the number of laser shots performed at the same location. In addition, laser sparks may also be used to study rock coatings. In particular, it will help to determine the depth of the transition between a coating and its underlying host rock [8].Moreover, as the start of the microphone recording is triggered on the laser pulse, the propagation time of the sound wave from the ground up to the microphone height is precisely measured. Therefore, it gives the sound speed along the sound propagation path. This parameter is used to estimate the ‘acoustic temperature’, an average of the air temperature over the two first meters from the ground [9]. First results on Martian targets:Up to sol 78 of the mission, the Supercam microphone has recorded the LIBS acoustic signal from 12 targets, including 3 soil targets and 2 depth profiles.The LIBS acoustic signal recorded on the float rock Hedgehog (sol 37) is represented in Fig. 3. The time series (Fig. 3a) shows a shot-to-shot decrease of the acoustic amplitude over the 30 shots fired in this target. The comparison with the hardness calibration curve presented in [4] suggests a soft target with a Vickers hardness lower than 10 and an ablated volume of about 200 µm. The frequency spectrum (Fig. 3b) is showing an acoustic bandwidth between 2 kHz and 10 kHz (see Fig. 3a), consistent with pre-flight calibrations [10]. Some gaps in the spectrum (5700 Hz, 10900 Hz, 14800 Hz) are indicative of destructive interferences induced by the reflection of the sound wave over the structure of the mast. Some wind-induced signal are also noticed in the time series (see red circles in Fig. 3a). They can be easily filtered, as their frequency content is lower than 500 Hz [6]. However, the influence of the turbulent atmosphere on the LIBS acoustic signal, needs to be assessed, as it was not tested in the laboratory.Figure 3 - Time series (a) and power spectral density (b) of the LIBS acoustic signal recorded on point #5 of the Hedgehog target (sol 37)As for the soil targets, the LIBS acoustic data show a clear decrease with increasing shot number due to shielding within the self-induced hole and also helps to determine whether the laser hit a coarse grain (louder sound) or fine-grained soil.Perspectives:The Supercam microphone has the unique capability to record the acoustic signal induced by the laser-induced plasma. The microphone will help to document the target hardness along the rover traverse and complement the chemical information provided by LIBS by adding an estimation of the ablated depth. This presentation will review results from all the microphone targets observed at the time of the conference.References[1] Wiens R. C et al., SSR 2021 https://doi.org/10.1007/s11214-020-00777-5 [2] Maurice S. et al., SSR 2021, https://doi.org/10.1007/s11214-021-00807-w [3] Chide B. et al, SAB 2019, https://doi.org/10.1016/j.sab.2019.01.008, [4] Chide B et al., SAB 2020 https://doi.org/10.1016/j.sab.2020.106000, 20, [5] Murdoch N. et al, this issue, [6] Stott et al., this issue, [7] Maurice S et al., JAAS 2016, doi:10.1039/c5ja00417a [8] Lanza N.L., LPSC 2020, 2807 [9] Chide B. et al., LPSC 2020 1366, [10] Murdoch N. 2019 PSS doi:10.1016/j.pss.2018.09.009.

Detection of indigenous organic matter (IOM) in rocks using molecular -laser -induced breakdown spectroscopy (LIBS) is reported. IOM refers to carbon -based compounds of variable complexity intimately associated with mineral and amorphous phases both in condensed phases and in a dispersed state spatially associated to mineral aggregates. The presence of IOM may provide valuable information in astrobiology about the possibility of past or present life on planetary bodies. Kerogen, charcoal, bitumen, and graphite are only some examples of IOM that may appear in rocks. This paper reports the detection of kerogen in oil shale (a sedimentary rock also containing dolomite, calcite, pyrite, quartz, and albite) from the LIBS study of CN and C2 emissions under simulated Martian conditions. A set of oil shale samples with variable concentrations of total organic carbon (TOC) ranging from 2.78% to 12.74% were analyzed. A careful LIBS analysis of molecular species associated within hydrocarbons confirmed the presence of organic matter derived from kerogen. A linear correlation between the CN and C2 emissions and the %TOC was observed. Using a simulated Martian atmosphere as surrounding gas, the limit of detection for organic matter was calculated in 0.42% TOC. Additionally, the potential interferences in geological samples for LIBS detection of molecular species were also evaluated. Results demonstrate that common elements in rocks such as Ca, Fe, K, Mg, Na and Si do not interfere with the detection of organics. In contrast, Ti at concentrations above 0.4% may induce false positive results using the CN emission at 388.34 nm. To overcome this inconvenience, the CN emission at 387.14 nm may be used which, although less sensitive, is free from titanium interference.

BACKGROUND:Thousands of micrometeorites fall to the Earth on a daily basis. Most of these meteorites have a rocky composition, but others are mainly composed of iron and nickel. Due to their small size, often ca. 100 μm in diameter, the process of searching for, collecting, and identifying these samples is remarkably tedious. In this work, we introduce a minimally invasive methodology for evaluating the full elemental composition of micrometeorites using optical emission spectroscopy of single particles produced by laser ablation of bulk targets. RESULTS:Bulk meteorite samples were directly ablated within an ablation cell. From few micrograms of ablated matrix, we originated dry aerosols consisting of multielemental particles which were representative of the sample chemistry. SEM images confirmed that the generated particles exhibited spherical geometry. Particles were first optically trapped in air and, then, analyzed by laser-induced breakdown spectroscopy (LIBS). LIBS spectra evidenced compositional differences among samples. For example, Campo de Cielo meteorite featured a high iron content due to its metallic nature whereas LIBS results for Jbilet Winselwan and NWA 869 suggested that pyroxene components dominated the composition of the samples. In contrast, NWA 13739 and Vaca Muerta contained high aluminum intensity, thus indicating that the feldspathic component was dominant, as then verified by XRD. The intra-sample compositional variability were quite satisfactory, as revealed by the RSD data, below 45 %. For quantitative analysis, the percentages of FeO, SiO2, Al2O3, Na2O, MgO, TiO2, CaO, K2O, MnO, SrO, Cr2O3, and Li2O were calculated using CF-LIBS. SIGNIFICANCE:This work demonstrates the applicability of laser excitation of individual particles in an optical trap for the multielemental analysis of meteorites. The methodology provides a complete overview of the samples, is capable of classificating them according to their main phases and yield preliminary quantitative information about those phases. Therefore, we present a minimally destructive pathway to be used as the first step in the inspection of these delicate samples. If the particles represent nanostructures inherent to the meteorites, it would constitute a major step in the analysis of extraterrestrial material that may provide fundamental insights into the structure and composition of the original materials at the microscale, a topic that remains an active area of research worldwide.

The acoustic wave produced alongside laser-induced plasmas can be used in conjunction with the recorded atomic spectra of plasma emission to expand the physicochemical information acquired from a single inspection event. Among the most interesting uses of acoustic information is the differentiation of mineral phases with similar optical responses coexisting in geological targets. In addition, laser-induced plasma acoustics (LIPAc) can provide data related to the inspected material's hardness, density, and compactness. In this paper, we present a dual acoustic-optic laser-based strategy for the generation of high-resolution surface images of mineral samples. By combining simultaneous multimodal LIBS (laser-induced breakdown spectroscopy) and LIPAc spectral data from laser-induced plasmas, we explore the mineralogical composition of rocks embedded in resin matrixes to distinguish their chemical composition as well as their crystal phases based on physical changes caused by the different spatial arrangements of the constituent atoms. The multispectral polyhedron created by merging singular optical maps, one per detected elements, and the coincidental acoustic map enhance the distinction between regions present within the matrix of a host rock as compared to the differentiation yielded by each technique when used separately. The chemical information guides the composition of the mineral phases in the host rock. Then, the physical information obtained from acoustics may reinforce the identification of the detected mineral phase, draw the geological history of the inspected section, and showcase possible transformations, mainly of polymorphic nature. To test the combination proposed herein, we also inspected a septarian nodule featuring an ensemble of mineral phases with different origins. Mixed optical and acoustic responses from laser-produced plasmas of this complex sample allowed us to obtain more specific information. This approach constitutes a reliable and high-throughput tool for studying the surface of geological samples, which can substantially supplement well-established techniques for mineralogical analysis such as Raman spectroscopy and X-ray diffraction.

Understanding the past habitable environments of Mars increases the requirement to recognize and examine modern analogs and to evaluate the mechanisms that may preserve biosignatures in them. The phenomenon that originates and preserves possible microbial biosignatures in mineral phases is of particular interest in astrobiology. On Earth, the precipitation of carbonate matrices can be mediated by bacteria. Besides microbialites and other sedimentary structures, carbonate formations can be observed in certain karstic caves. The present work is focused on the remote laser-induced breakdown spectroscopy (LIBS) characterization of cyanobacteria, exploring the possibilities for identification and discrimination on carbonate substrates. For this purpose, the extremophile cyanobacterium Chroococcidiopsis sp. (collected from the Nerja Cave, Malaga, Spain) was analyzed under laboratory-simulated martian conditions in terms of chemical composition and gas pressure. LIBS results related to acquired molecular emission features allowed bacterial differentiation from the colonized mineral substrate. In addition, the limits of detection were estimated with a laboratory-grown culture of the cyanobacterium Microcystis aureginosa. Our results reveal LIBS's capability to detect biological traces under simulated martian conditions. Additionally, the time-resolved analysis of the biological samples demonstrates the selection of optimal temporal conditions as a critical parameter for the preferential acquisition of molecular species in organic material.

Inspection of geological material is one of the main goals of the Perseverance rover during its journey across the landscape of the Jezero crater in Mars. NASA's rover integrates SuperCam, an instrument capable of performing standoff characterization of samples using a variety of techniques. Among those tools, SuperCam can perform laser-induced breakdown spectroscopy (LIBS) studies to elucidate the chemical composition of the targets of interest. Data from optical spectroscopy can be supplemented by simultaneously-produced laser-produced plasma acoustics in order to expand the information acquired from the probed rocks thanks to the SuperCam's microphone (MIC) as it can be synchronized with the LIBS laser. Herein, we report cover results from LIBS and MIC during Perseverance's first 380 sols on the Martian surface. We study the correlation between both recorded signals, considering the main intrasample and environmental sources of variation for each technique, to understand their behavior and how they can be interpreted together towards complimenting LIBS with acoustics. We find that louder and more stable acoustic signals are recorded from rock with compact surfaces, i.e., low presence loose particulate material, and harder mineral phases in their composition. Reported results constitute the first description of the evolution of the intensity in the time domain of shockwaves from laser-produced plasmas on geological targets recorded in Mars. These signals are expected contain physicochemical signatures pertaining to the inspected sampling positions. As the dependence of the acoustic signal recorded on the sample composition, provided by LIBS, is unveiled, the sound from sparks become a powerful tool for the identification of mineral phases with similar optical emission spectra.

A fragment of the NWA 2975 Martian meteorite, an enriched basaltic shergottite, was analysed to complete its geochemical characterisation performed 10 years ago. By this means, the feasibility of the employed techniques in a combined way for present and future space exploration missions can be tested. For this aim, Raman spectroscopy was used supported by micro energy dispersive X-ray fluorescence (mu-EDXRF) and laser-induced breakdown spectroscopy (LIBS) for an accurate interpretation of molecular and elemental results. Raman spectroscopy results from two setups, InVia from Renishaw and RLS Simulator, were compared. The major minerals detected by Raman spectroscopy were pyroxenes (mainly augite, pigeonite and enstatite) and plagioclases (mainly shocked maskelynite). Raman spectroscopy allowed defining different metal compositions for these main minerals based on the secondary Raman spectroscopy bands in the 200-500 cm(-1) region. In addition, other minerals were found such as merrillite, as well as pyrrhotite and apatite, in several veins and cracks of the meteorite, in agreement with the initial report by the Meteoritical Bulletin. Moreover, it should be highlighted that coesite was found for the very first time in this meteorite.

In the present work, a wavelength-selected plasma imaging analysis system is presented and used to track photons emitted from single-trapped nanoparticles in air at atmospheric pressure. The isolated nanoentities were atomized and excited into plasma state using single nanosecond laser pulses. The use of appropriate wavelength filters alongside time-optimized acquisition settings enabled the detection of molecular and atomic emissions in the plasma. The photon detection efficiency of the imaging line resulted in a signal > 400 times larger than the simultaneously-acquired dispersive spectroscopy data. The increase in sensitivity outlined the evolution of diverse physicochemical processes at the single particle scale which included heat and momentum transfer from the plasma into the particle as wells as chemical reactions. The imaging detection of excited fragments evidenced different diffusion kinetics and time frames for atoms and molecules and their influence upon both the spectroscopic emission readout and fabrication processes using the plasma as a reactor. Moreover, the origin of molecular species, whether naturally-occurring or derived from a chemical reaction in the plasma, could also be studied on the basis of compositional gradients found on the images. Limits of detection for the inspected species ranged from tens to hundreds attograms, thus leading to an exceptional sensing principle for single nanoentities that may impact several areas of science and technology.

Soil assessment is important for mobile robot planning and navigation on natural and planetary environments. Terramechanic characteristics can be inferred from the thermal behaviour of soils under the influence of sunlight using remote sensors such as Long-Wave Infrared cameras. However, this behaviour is greatly affected by the low atmospheric pressures of planets such as Mars, so practical models are needed to relate robot remote sensing data on Earth to target planetary exploration conditions. This article proposes a general framework based on multipurpose environmental chambers to generate representative diurnal cycle dataset pairs that can be useful to relate the thermal behaviour of a soil on Earth to the corresponding behaviour under planetary pressure conditions using remote sensing. Furthermore, we present an application of the proposed framework to generate datasets using the UMA-Laserlab chamber, which can replicate the atmospheric \ch{CO2} composition of Mars. In particular, we analyze the thermal behaviour of four soil samples of different granularity by comparing replicated Martian surface conditions and their Earth's diurnal cycle equivalent. Results indicate a correlation between granularity and thermal inertia that is consistent with available Mars surface measurements recorded by rovers. The resulting dataset pairs, consisting of representative diurnal cycle thermal images with heater, air, and subsurface temperatures, have been made available for the scientific community.

Dataset for the article titled "Thermal Vision for Soil Assessment in a Multipurpose Environmental Chamber under Martian Conditions towards Robot Navigation".

Owing to the exceedingly small mass involved, complete elemental characterization of single nanoparticles demands a highly precise control of signal background and noise sources. LIBS has demonstrated remarkable merits for this task, providing a unique tool for the multielemental analysis of particles on the attogram-picogram mass scale. Despite this outstanding sensitivity, the air plasma acting as a heat source for particle dissociation and excitation is a meddling agent, often limiting the acquisition of an accurate sample signature. Although thermal effects associated with ultrashort laser pulses are known to be reduced when compared to the widely used nanosecond pulse duration regime, attempts to improve nanoinspection performance using ultrafast excitation have remained largely unexplored. Herein, picosecond laser pulses are used as a plasma excitation source for the elemental characterization of single nanoparticles isolated within optical traps in air at atmospheric pressure. Results for picosecond excitation of copper particles lead to a mass detection limit of 27 attogram, equivalent to single particles 18 nm in diameter. Temporally and wavelength-resolved plasma imaging reveals unique traits in the mechanism of atomic excitation in the picosecond regime, leading to a deeper understanding of the interactions occurring in single nanoparticle spectroscopy.

Before the Perseverance rover landing, the acoustic environment of Mars was unknown. Models predicted that: (1) atmospheric turbulence changes at centimetre scales or smaller at the point where molecular viscosity converts kinetic energy into heat 1 , (2) the speed of sound varies at the surface with frequency 2 , 3 and (3) high-frequency waves are strongly attenuated with distance in CO 2 (refs. 2 – 4 ). However, theoretical models were uncertain because of a lack of experimental data at low pressure and the difficulty to characterize turbulence or attenuation in a closed environment. Here, using Perseverance microphone recordings, we present the first characterization of the acoustic environment on Mars and pressure fluctuations in the audible range and beyond, from 20 Hz to 50 kHz. We find that atmospheric sounds extend measurements of pressure variations down to 1,000 times smaller scales than ever observed before, showing a dissipative regime extending over five orders of magnitude in energy. Using point sources of sound (Ingenuity rotorcraft, laser-induced sparks), we highlight two distinct values for the speed of sound that are about 10 m s −1 apart below and above 240 Hz, a unique characteristic of low-pressure CO 2 -dominated atmosphere. We also provide the acoustic attenuation with distance above 2 kHz, allowing us to explain the large contribution of the CO 2 vibrational relaxation in the audible range. These results establish a ground truth for the modelling of acoustic processes, which is critical for studies in atmospheres such as those of Mars and Venus.

The shockwave produced alongside the plasma during a laser-induced breakdown spectroscopy event can be recorded as an acoustic pressure wave to obtain information related to the physical traits of the inspected sample. In the present work, a mid-level fusion approach is developed using simultaneously recorded laser-induced breakdown spectroscopy (LIBS) and acoustic data to enhance the discrimination capabilities of different iron-based and calcium-based mineral phases, which exhibit nearly identical spectral features. To do so, the mid-level data fusion approach is applied concatenating the principal components analysis (PCA)-LIBS score values with the acoustic wave peak-to-peak amplitude and with the intraposition signal change, represented as the slope of the acoustic signal amplitude with respect to the laser shot. The discrimination hit rate of the mineral phases is obtained using linear discriminant analysis. Owing to the increasing interest for in situ applications of LIBS + acoustics information, samples are inspected in a remote experimental configuration and under two different atmospheric traits, Earth and Mars-like conditions, to validate the approach. Particularities conditioning the response of both strategies under each atmosphere are discussed to provide insight to better exploit the complex phenomena resulting in the collected signals. Results reported herein demonstrate for the first time that the characteristic sample input in the laser-produced acoustic wave can be used for the creation of a statistical descriptor to synergistically improve the capabilities of LIBS of differentiation of rocks.

Arsenic determination by LIBS at low levels is a challenging analytical task due to its low sensitivity, limited number of available emission lines, and spectral interferences. In this work, a LIBS system with controlled atmosphere for the determination of arsenic at low concentrations in copper ores is presented. Under optimized conditions, the As lines at 278.06 nm (with interference of Fe II) and 286.04 nm were able to be used for measurements. Improved analytical figures of merits were obtained using deconvoluted spectra and artificial neural network based on a radial basis function (ANN-RBF), specific values of relative error percentage (REP %), root mean square error of prediction (RMSEP) and intervals of limits of detection (LOD) and quantification (LOQ) were 18.6 wt%, 0.037 wt%, 0.045-0.062 wt% and 0.135-0.185 wt%, respectively.