Evidence of chemical reactions in the hydroxyapatite laser ablation plume with a water atmosphere

The expansion dynamics of the ablation plume generated by KrF laser irradia tion of hydroxyapatite targets in a 0.1 mbar water atmosphere has been stud ied by fast intensified charge coupled device imaging with the aid of optic al bandpass filters. The aim of the filters is to isolate the emission of a single species, which allows separate analysis of its expansion. Images ob tained without a filter revealed two emissive components in the plume, whic h expand at different velocities for delay times of up to 1.1 mu s. The dyn amics of the first component is similar to that of a spherical shock wave, whereas the second component, smaller than the first, expands at constant v elocity. Images obtained through a 520 nm filter show that the luminous int ensity distribution and evolution of emissive atomic calcium is almost iden tical to those of the first component of the total emission and that there is no contribution from this species to the emission from the second compon ent of the plume. The analysis through a 780 nm filter reveals that atomic oxygen partially diffuses into the water atmosphere and that there is a con tribution from this species to the emission from the second component. The last species studied here, calcium oxide, was analyzed by means of a 600 nm filter. The images revealed an intensity pattern more complex than those f rom the atomic species. Calcium oxide also contributes to the emission from the second component. Finally, all the experiments were repeated in a Ne a tmosphere. Comparison of the images revealed chemical reactions between the first component of the plume and the water atmosphere. (C) 1999 American I nstitute of Physics.