ANALYSIS OF THE PLASMA EXPANSION DYNAMICS BY OPTICAL TIME-OF-FLIGHT MEASUREMENTS

The laser plasma plume expansion induced by UV nanosecond and IR picosecond irradiation of an Y-Ba-Cu-O target has been studied using optical time-of-flight spectra. Nanosecond ablation leads to a broad particle velocity distribution already at the first stage of expansion because of a temperature dispersion of the ejected species. Picosecond irradiation reduces this kind of dispersion and allows one to observe properly the particle expansion dynamics. The velocities of the charged particles are inversely proportional to the square root of the atomic mass. The velocities of the neutral atoms exhibit much weaker dependence on the atomic mass and are determined by collisional expansion. The time-of-flight spectra reveal a double population of YO+ molecules with different velocity distribution.