Analyses of Gas-Phase Reactions during Pulsed-Laser Ablation using Laser-induced Fluorescence-, Absorption- and Emission- Spectroscopy

摘要

The role of gas-phase reactions during pulsed-laser ablation in low-pressure atmospheres has been investigated by time- and space- resolved spectroscopic measurements. Thus, excited states species have been detected by optical emission spectroscopy. The population densities were determined in an absolute scale after calibration of the spectroscopic apparatus. Complementary information was obtained by detecting ground-state species using laser-induced fluorescence (LIF) spectroscopy. Therefore, a beam expander was used to transform the dye laser probe beam in a thin plane section of 0.2 x 40 mm~2 dimension. Using a fast intensified charged coupled device for photon detection, three-dimensional number density mapping of ground-state species was possible. The LIF measurements have been calibrated by additional absorption measurements. As a result, a detailed picture of the time- and space evolution of the plasma plume from the target towards the substrate was acquired making in evidence the formation of diatomic reaction products as a result of interaction between the ablated material and the ambient gas. In order to outline the different reactivity of nitridation and oxidation processes, measurements have been performed during ablation of aluminium, graphite and titanium targets in either nitrogen and oxygen low-pressure atmospheres. The measured densities of atomic and molecular species were compared to those computed for local thermal equilibrium.