Florian Trichard

Laser-induced breakdown spectroscopy for elemental characterization of calcitic alterations on cave walls

Cave walls are affected by different kinds of alterations involving preservative issues in the case of ornate caves, in particular regarding the rock art covering the walls. In this context, coralloids correspond to a facies with popcorn-like aspect belonging to the speleothem family, mostly composed of calcium carbonate. The elemental characterization indicates the presence of elements that might be linked to the diagenesis and the expansion of the alterations as demonstrated by prior analyses on stalagmites. In this study, we report the use of laser-induced breakdown spectroscopy (LIBS) to characterize the elemental composition of one coralloid sample with a portable instrument allowing punctual measurements and a laboratory mapping setup delivering elemental images with spatial resolution at the micrometric scale, being particularly attentive to Mg, Sr, and Si identified as elements of interest. The complementarity of both instruments allows the determination of the internal structure of the coralloid. Although a validation based on a reference technique is necessary, LIBS data reveal that the external layer of the coralloid is composed of laminations correlated to variations of the LIBS signal of Si. In addition, an interstitial layer showing high LIBS signals for Fe, Al, and Si is interpreted to be a detrital clay interface between the external and the internal part of the coralloid. These preliminary results sustain a possible formation scenario of the coralloid by migration of the elements from the bedrock.

Evaluation of a compact VUV spectrometer for elemental imaging by laser-induced breakdown spectroscopy: application to mine core characterization

This work introduces a new approach to perform LIBS elemental imaging in the vacuum ultraviolet (VUV) wavelength range by using an argon purged probe coupled to a compact spectrometer. In spite of several important elements for geological and industrial applications such as S, P, As, B, C, or Zn presenting strong lines in the VUV range, the need for using specific optics and working under oxygen-free conditions has limited the extension of LIBS systems available for such a range. Herein, we present an adaptation of our LIBS imaging instrumentation to access the VUV while operating under ambient conditions. The proposed detection system is based on an optical probe directly coupled to a Maya2000Pro compact spectrometer (Ocean Optics), all purged with argon. The technical design along with a detailed evaluation of the VUV probe is addressed. The possibility of using this VUV probe for LIBS imaging is also investigated by studying a Canadian mine core sample with special emphasis on the detection of sulfur. In addition to sulfur, more than 15 elements including P, As, C, Ca, Si, Mo, B, and Zn have also been detected. Elemental images covering sample surfaces in the range of cm2 with a micrometric spatial resolution (10 μm) are presented. A detection limit of 0.2 wt% for sulfur is demonstrated in a single shot configuration. These results open new perspectives for both conventional LIBS and LIBS-based imaging in various application fields.

Characterization of foreign materials in paraffin-embedded pathological specimens using in situ multi-elemental imaging with laser spectroscopy

Pathologists typically encounter many disparate exogenous materials in clinical specimens during their routine histopathological examinations, especially within the skin, lymph nodes, and lungs. These foreign substances may be free extracellular deposits or induce several clinical abnormalities or histopathological patterns. However, pathologists almost never investigate or report the chemical nature of exogenous metals in clinical specimens due to a lack of convenient and available technologies. In this paper, a novel strategy based on laser-induced breakdown spectroscopy (LIBS) technology is evaluated for in situ multi-elemental tissue imaging. The improved procedures allow visualization of the presence of chemical elements contained within paraffin-embedded specimens of medical interest with elemental images that are stackable with conventional histology images. We selected relevant medical situations for which the associated pathology reports were limited to the presence of lymphohistiocytic and inflammatory cells containing granules (a granuloma and a pseudolymphoma) or to lymph nodes or skin tissues containing pigments or foreign substances. Exogenous elements such as aluminum, titanium, copper, and tungsten were identified and localized within the tissues. The all-optical LIBS elemental imaging instrument that we developed is fully compatible with conventional optical microscopy used for pathology analysis. When combined with routine histopathological analysis, LIBS is a versatile technology that might help pathologists establish or confirm diagnoses for a wide range of medical applications, particularly when the nature of external agents present in tissues needs to be investigated.

Exploration of megapixel hyperspectral LIBS images using principal component analysis

Laser-Induced Breakdown Spectroscopy (LIBS) has achieved promising performance as an elemental imaging technology, and considerable progress has been achieved in the development of LIBS over the last several years, which has led to great interest in the use of LIBS in various fields of applications. LIBS is a highly attractive technology that is distinguished by its table top instrumentation, speed of operation, and operation in ambient atmosphere, able to produce megapixel multi-elemental images with micrometric resolution (10 μm) and ppm-scale sensitivity. However, the points that limit the development of LIBS are undeniably the expertise and the time required to extract a relevant signal from the LIBS dataset. The complexity of the emission spectra (e.g., elemental responses, structure of the baseline), the high dynamic range of measurement (i.e., possibility to image major to trace elements), and the large number of spectra to process require new data analysis strategies. Such new strategies are particularly critical for multi-phase materials. In this paper, we report a new methodology based on the well-known Principal Component Analysis (PCA) approach for the multivariate hyperspectral analysis of LIBS images. The proposed methodology is designed for large, raw, and potentially complex series of LIBS spectra, that allows various and exhaustive levels of information to be extracted (including the characterization of mineral phases, assessment of the measurement and identification of isolated elements) and facilitates the manipulation of such hyperspectral datasets.

Elemental imaging by laser-induced breakdown spectroscopy for the geological characterization of minerals

Geological studies increasingly require highly sensitive elemental techniques able to image the distribution of elements in minerals with microscopic-scale resolution. In this paper, we present an evaluation of megapixel laser-induced breakdown spectroscopy (LIBS) imaging for the geological characterization of minerals. The study is conducted on a hydrothermal ore sample with a complex mineral structure involving five different mineral phases (galena, sphalerite, chalcopyrite, quartz and ankerite). A new methodology of data treatment adapted to a multi-phase material and megapixel LIBS imaging is also detailed. We demonstrate for the first time, to our knowledge, that LIBS-imaging technology is able to both detect and image rare earth elements (here La and Y) in carbonate as well as substituents present at the ppm-scale level in various mineral phases (i.e., cadmium in sphalerite; bismuth, silver and antimony in galena; beryllium and aluminum in quartz; and tin in chalcopyrite). These results appear extremely promising for the geological domain and should pave the way for innumerable applications.