NEGATIVE-ION EMISSION DURING LASER-ABLATION OF MULTICOMPONENT MATERIALS

The time of flight technique coupled with an electrostatic energy filt er has been used for composition and energy-distribution analysis of t he ion species emitted during laser ablation of multicomponent materia ls Y-Ba-Cu-O, Pb-Sn-Te. The negative-ion output and kinetic-energy dis tribution as a function of the laser wavelength and the laser fluence on the target were measured. A high output of the negative ions of mat rix elements comparable with the positive-ion emission was detected. T he barium negative-ion formation was observed in spite of the negative electron affinity of alkaline earth elements in the ground electronic state. The mechanism of negative-ion formation based on the ternary c ollisional recombination in the laser plasma is analyzed.