Imaging of the Expansion of Femtosecond-Laser-Produced Silicon Plasma Atoms by Off-Resonant Planar Laser-Induced Fluorescence

Planar laser-induced fluorescence measurements were used to investigate the expansion dynamics of a femtosecond laser-induced plasma. Temporally and spatially resolved measurements were performed to monitor the atoms that were ablated from a silicon target. A dye laser ( (lambda) = 288.16 nm) was used to excite fluorescence signals. The radiation of an off-resonant transition (Si 390.55 nm) was observed at different distances from the target surface. This allowed easy detection of the ablated Si atoms without problems caused by scattered laser light. Abel inversion was applied to obtain the radial distribution of the Si atoms. The atom distribution in the plasma shows some peculiarities, depending on the crater depth.