Femtosecond (fs) filaments delivering substantial peak intensities at remote locations are being exploited in several practical applications together with in situ remote/standoff (ST) investigations. The optical emissions produced during the filament interaction were analyzed to study the composition of distant targets. In this article, we present the comparative results obtained from qualitative studies of territorial rocks (collected from the central Dharwar craton, South India) in the near-field and in the standoff mode with fs laser induced breakdown spectroscopy (fs LIBS) and fs filament induced breakdown spectroscopy (fs FIBS) techniques. The granitoids possessing distinct mineralogical and chemical characteristics were analyzed in their original form in ambient air from a distance of (i) ∼15 cm with tightly focused fs pulses in near-field configuration and (ii) ∼6.5 m using fs filaments in standoff configuration. Various atomic emission lines belonging to major elements such as Ca, K, Na, Al, Fe and Mg were identified and labelled from both fs LIBS and fs FIBS spectra of each sample. Few spectral lines corresponding to trace elements such as Ba, Ti and V were also identified. Furthermore, Mg/Ca, Fe/Ca, Mg/Al, Ca/Al, Mg/Si and Fe/Si ratios were considered to highlight the differences that could serve for the classification of these granitoids. A good correlation of constituent element spectral line intensities, especially in the standoff mode, was observed with weight percentage of their oxides obtained from X-ray fluorescence (XRF) data. The overall change in relative standard deviation (RSD%) of major spectral intensities for a sample was observed to be lower (5–25%) in the standoff case in comparison to that of the near-field configuration (16–38%). Furthermore, the results from the principal component analysis (PCA) employed in tandem with normalized/unnormalized fs ST-FIBS data of these geological rock samples demonstrated a high degree of qualitative classification in comparison to normalized/unnormalized fs LIBS data. Therefore, we firmly believe that the results from the present work clearly extend the application of fs filaments to standoff analysis of geological beds and mineral ores under the ambient atmospheric conditions intended for unpleasant environment detection.

中文翻译：

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固定飞秒丝诱导击穿光谱法对地质材料进行分类

飞秒（fs）灯丝可在偏远地区提供相当大的峰值强度，在一些实际应用中以及在现场进行开发远程/对峙（ST）调查。分析了灯丝相互作用过程中产生的光发射，以研究远距离目标的组成。在本文中，我们介绍了使用fs激光诱导击穿光谱法（fs LIBS）和fs灯丝在近场和对峙模式下对陆地岩石（从印度南部中央Dharwar克拉通采集）进行定性研究获得的比较结果。感应击穿光谱（fs FIBS）技术。在（i）〜15 cm的距离内以近场构型将fs脉冲紧紧聚焦，在（ii）〜6.5 m的情况下使用远距离构型的fs细丝在环境空气中以原始形式分析具有独特矿物学和化学特性的花岗岩。属于主要元素的各种原子发射线，例如钙，钾，钠，铝，从每个样品的fs LIBS和fs FIBS光谱中鉴定并标记了Fe和Mg。还识别出了与痕量元素（例如Ba，Ti和V）相对应的光谱线。此外，Mg / Ca，Fe / Ca，Mg / Al，Ca / Al，Mg / Si和Fe / Si之比被认为是为了突出可用于这些类花岗岩分类的差异。观察到组成元素光谱线强度的良好相关性，尤其是在对峙模式下，与它们从X射线荧光（XRF）数据获得的氧化物的重量百分比具有良好的相关性。与近场配置（16-38％）相比，在隔离情况下，样品的主要光谱强度的相对标准偏差（RSD％）的总体变化较低（5-25％）。此外，与归一化/非归一化的fs LIBS数据相比，这些地质岩石样品的归一化/非归一化fs ST-FIBS数据与主成分分析（PCA）结合使用的结果证明了高度的定性分类。因此，我们坚信，当前工作的结果清楚地将fs细丝的应用范围扩展到了旨在检测​​不良环境的周围大气条件下的地质床层和矿物矿石的间隙分析。