Fluence dependence of hydroxyapatite laser ablation plumes

Plumes generated by laser ablation of hydroxyapatite (HA) targets under div erse irradiation conditions have been analysed by means of fast intensified CCD imaging and optical emission spectroscopy. Images obtained at four dif ferent laser fluences (1, 1.5. 2.6 and 3.5 J/cm(2)) have revealed the prese nce of two separated emissive components in the plume for delay times up to 1 mu s after the laser pulse. The relative emission intensity between both components strongly depends on the magnitude of the fluence and so do thei r velocities of expansion. Spectra as recorded have shown that at low fluen ces, molecular species predominate over atomic ones, whereas at high fluenc es, atomic species are the predominant ones. Images obtained with the aid o f bandpass filters have revealed that the nature of the faster emissive com ponent in the plume is mainly atomic, whereas emission from the second one mainly arises from excited molecular radicals. (C) 1998 Published by Elsevi er Science Ltd. All rights reserved.