Calibration-free laser-induced breakdown spectroscopy (CF-LIBS) is a quantitative analysis method that takes advantage of the self-consistency of plasma spectra. It includes numerical approximation methods by calculating element-specific spectral radiation densities that can be used to determine the element contents of sample. As this requires no calibration, it is particularly suitable for unknown sample compositions or large variety of sample composition. Additionally, CF-LIBS does not require any sample preparation, which is why it is particularly suitable for real-time and in-line analysis of complex preparation processes; be it for process monitoring or process optimization.

To calculate the element-specific spectral radiation densities accurately, an essential prerequisite is the high accuracy of the quantitative results of such a measurement. This includes, but is not limited to, a high-resolution spectrometer that is also temperature-stabilized, i.e. temperature fluctuations of well below 1 K between characterization and actual measurement.

In the present work, samples of various soils contents were analyzed in collaboration with the Laboratoire des Lasers, Plasmas et Procédés Photoniques in Marseille, France. For this purpose, a temperature-stabilized spectrometer (Aryelle Butterfly, LTB, Berlin, DE) with a spectral resolving power of 14000 and 9100 for the ultraviolet and visible/infrared spectral ranges, respectively, and an absolute measurement accuracy of 0.004 nm was used. The pellet was sampled with a 266 nm laser beam at 6 mJ energy, with 100–300 individual shots averaged to produce a single spectrum. The evaluations shown are based on average spectra of 100 - 300 individual spectra. Additionally, the ablation volume per laser shot (Fig. 1), the plasma size and the homogeneity in the surface and depth of the samples were measured. As shown in Fig. 1, the sample compositions derived from CF-LIBS were in good agreement with the XRF-references. All of which were achieved without any form of calibration of the system.