Velocity measurement of the ablated particles during picosecond laser ablation

The laser-induced plasma plume dynamics for picosecond laser ablation of silicon and YBaCuO targets have been studied using optical time-of-flight spectra. The picosecond pulse ablation allows one to reduce the temperature and velocity dispersion of the ablated species. The expansion velocities of the ionized species show an inverse square root dependence vs. the atomic mass and are proportional to their charge. The velocities of the neutral atoms exhibit a much weaker dependence vs. atomic mass. The formation of a charge separation region was observed during plasma plume expansion. These experimental results support the Coulomb expansion mechanism of the laser-induced plasma.