Threshold level laser photoablation of crystalline silver: Ejected ion translational energy distributions

Publisher Website
Google Scholar
Abstract
We have conducted an experiment which measures, for a single laser shot, the ejected mass and nascent velocity distributions of ionic species ablated at laser fluences near the threshold for ion production. Our results show that for a crystalline silver target, the laser-ablated ion products are ejected with fixed kinetic energy equal to 9±1 eV (3 eV FWHM). The kinetic energy of the ejecta (Ag+,Ag+2, adsorbed Fe+) do not vary with wavelength (351 and 248 nm), nor with the ion product mass, and within limits are independent of the incident laser intensity. We do see a wavelength dependence in the threshold for ion production and in the dimer/monomer (Ag+/Ag+2) ion ratio. A number of possible mechanisms are presented to explain the data, although none is without some objection. Among these, the process whereby desorption is induced by electronic transitions (DIET processes) has some merit in explaining our data.