Positive Ion Emission from Excimer Laser Excited MgO Surfaces

We report measurements of the energy and angular distributions of positive ions (principally ${\mathrm{Mg}}^{+}$) photodesorbed from polished MgO crystals exposed to 248 nm excimer laser radiation. At low laser fluences, kinetic energies of several eV are observed and angular distributions are highly peaked in the direction perpendicular to the surface. We present an electrostatic model involving Coulombic repulsion of positively charged ions repelled by photoionized $F$ centers.