Comparison of light capturing approaches in Laser-Induced Breakdown Spectroscopy (LIBS) for multichannel spectrometers

LIBS technique requires the spectroscopic analysis of the light emitted by a laser-induced plasma plume. One challenge of the different approaches to capture the plasma light emission is the significant shot-to-shot variations of the plume inhomogeneities, position, and morphology. This is even more challenging when multichannel CCD spectrometers are used, because the light should be homogeneously divided among multiple capturing optical fibers (typically up to 8 fibers) with stable spectral efficiency for all channels. Otherwise, any further analysis of the atomic emission spectra involving multiple channels, such as line intensity ratios, Boltzmann plots, or calibration-free LIBS, could be compromised by the morphology-dependent spectral artifacts induced by the collection optics. In this work, we assess the performance of several collection optics in terms of overall capturing efficiency and channel-to-channel variations due to changes in plasma morphology. Results clearly show that this could be an issue even with the approaches with the best spatial homogenization, including optical fibers and Köhler optics.