Laser-Induced Breakdown Spectroscopy in the Vacuum-Ultraviolet Wavelength Regime for the Application in Planetary Exploration

Kurzfassung

This thesis investigates the application of laser-induced breakdown spectroscopy (LIBS) with detection in the vacuum ultraviolet (VUV) spectral range for in-situ space exploration. For LIBS, a pulsed laser is tightly focused onto the sample, thereby ablating material and exciting a luminous plasma. The atoms and ions contained in the plasma radiate light of characteristic wavelengths, which can be analysed with spectrometers. The spectral analysis allows to identify the chemical elements in the plasma, which are assumed to be representative for the elements contained in the sample. With LIBS, all elements can be detected. However, especially the non-metal elements are challenging to detect because their strongest lines are located in the VUV spectral range, i.e. below 200 nm, which is often not investigated. Detection in this range brings its own challenges, since large parts of the radiation spectrum are absorbed by the atmosphere surrounding the sample. On celestial bodies without an atmosphere, such as the Moon, the ambient conditions are well suited for VUV-LIBS analyses. In such a scenario, a better detectability for the otherwise challenging elements C, Cl, H, N, O, P and S is expected compared to LIBS in the usually employed detection range above 200 nm. The results shown in this thesis indicate that VUV-LIBS is promising for the improved detection of light elements such as S and Cl in a lunar context. However, more extensive studies with an optimized set-up are necessary to properly assess the true capabilities of the method and to further reduce the detection limits. Although emission from the most abundant chemical elements in geological samples, Al, Si and O, could be reliably detected in all samples containing them, VUV-LIBS might in the end be best used in combination with LIBS in the UV-VIS range or with other analytical techniques, because the major rock forming elements Ca, Na and Mg hardly show emission lines in the VUV spectral range.