Pulsed laser positive ion desorption from a model hydrated inorganic crystal CaHPO P2H O/at 248 nm

We examine the laser-induced positive ion emission of a typical, wide band gap, hydrated inorganic single crystal, CaHPO4P2H2O brushite., at 248 nm KrF excimer.in vacuum. As-grown brushite is quite resistant to laser damage and yields little ion emission at fluences below 1 Jrcm2. In the presence of surface damage by abrasion or heating-induced transformations, intense laser-induced ion emission appears at lower fluences. The ion energy and fluence dependence are consistent with a defect mediated, multiple photon emission mechanism. In particular, the transport of hydrated Caq to the surface, followed by adsorption at anion defects and removal of water by evaporation., can provide an ideal environment for ion emission. The implications with regard to the UV laser ablation of hydrated environmental and biological minerals are discussed. q1998 Elsevier Science B.V.