RESUMO
A systematic study of the spectrally resolved atomic emission arising from the laser ablation of YBa(2)Cu(3)O(7-x) targets in the presence of an oxygen background reveals statistically distributed populations with characteristic temporally averaged electronic temperatures of 0.28-0.38 eV, 0.28-0.37 eV, and 0.40-0.48 eV for neutral barium, yttrium, and copper, respectively. The higher electronic temperatures of the lighter copper atoms cannot be explained by the effects of temporal averaging, as the time-of-flight spectra are similar for all three atomic species. The electronic temperatures decline slowly with distance from the target, with a characteristic length of 20 to 200 mean free paths. The plume kinetic energies determined from gated imagery recorded time-of-flight spectra are much higher, 3-250 eV, suggesting a small fraction of the kinetic energy is converted to electronic excitation during each collision at the shock contact front. A correlation between electronic temperatures and shock strength reduces the dimensionality of the dependence on pressure and target distance. The dependence of electronic temperature on deposition condition is weak, suggesting the electronic state distribution is a poor candidate as a monitor for process control during the manufacture of coated conductors.
