| Popis: |
Laser-induced breakdown spectroscopy (LIBS) offerers the possibility to study rinds and layered structures in a sample by creating a crater by employing repeated laser ablation. Previous studies have shown that the existence of craters can cause significant changes in both the thermal properties and the composition of the plasma. The occurrence of contributions to the plasma thorough plasma-crater interactions was studied for Martian atmospheric conditions using a sample consisting of a dolomite slab covered by an aluminum foil. The experiment showed that significant amounts of aluminum was present in the plasma after the laser had penetrated the foil completely. In four craters of different depth and a diameter of 1400 μm the aluminum content of the plasma was significantly lower when using a 600 μm beam diameter for spectral acquisition as compared to when using a 1400 μm beam. Additionally the differential penetration due to the Gaussian shape of the beam intensity profile was found to be a complicating factor by reducing the depth resolution of the LIBS measurement. The change in the composition of the plasma due to elemental fractionation was studied by observing the intensity of selected Al, Ca, Fe, K, Mg, Na and Si emission lines throughout crater formation. A homogeneous basalt slab was analyzed under Martian atmospheric conditions. Only Mg and Na exhibited a change in line intensity throughout the crater formation that is large enough to indicate a change in the composition of the plasma. When acquiring spectra using a beam with a diameter of 600 μm in craters with a diameter of 1400 μm the rate of change in line intensity for the different elements were not significantly different from the reference values. The conclusion is that using different two beam diameter, a larger for crater formation and a smaller for spectral acquisition improves the ability to separate between different layers in the sample without increasing the problem of changes in fractionation. Validerat; 20110519 (anonymous) |
