Laser-induced fluorescence probing during pulsed-laser ablation for three-dimensional number density mapping of plasma species

Laser-induced fluorescence spectroscopy was employed to measure ground state number densities of atoms and molecules in plasma plumes generated by pulsed-laser ablation of Al, C and Ti targets in N2 or O2 low-pressure atmospheres. A beam expander was used to transform the dye laser beam in a thin plane section of 0.2x40 mm2 dimension crossing the plasma through its symmetry axis. Using a fast intensified charged coupled device matrix for fluorescence detection, three-dimensional number density mapping of plasma species was acquired. Calibration of the measured ground state densities in an absolute scale was performed by additional absorption measurements. According to the plasma temperature, the density of atoms and molecules and their total number in the plasma plume were estimated. The species densities were compared to those obtained by intensity calibrated emission spectroscopic measurements. The time- and space-evolution of atomic and molecular densities gives information about gas-phase reactions due to the interaction of the ablated material with the surrounding low-pressure gas. The results contribute to a better understanding of thin film synthesis by reactive pulsed-laser deposition. (author)