Analysis of the expansion of hydroxyapatite laser ablation plumes

Fast intensified CCD imaging has been used to analyze the expansion of hydroxyapatite laser ablation plumes after KrF excimer laser irradiation. Images as obtained have shown the presence of three different glow regions. A plume-like plasma followed by a smaller and slower plasma cloud freely expand from the first instants of time after the laser pulse. A third glow region, the expansion of which begins over 50 μs after the laser impingement, is formed by hot particles leaving the target. The same experiment has been repeated under the same conditions by changing the laser wavelength to that of ArF. Only the first two plasma clouds have been identified in this case. Finally, in order to relate the detection of hot particles with the presence of droplets in HA pulsed laser deposited films, scanning electron micrographs of the deposited coatings have been obtained showing a much lower density of droplets in the case of ArF irradiation than in that of KrF.