Laser ablation rate of hydroxylapatite in different atmospheres

Hydroxylapatite (Ca10(PO4)6(OH)2) is a calcium phosphate used as coating for dental and orthopaedic implants, because its composition and structure are similar to the mineral part of bone. Pulsed laser deposition has been applied as an alternative to the commercial technique for the production of hydroxylapatite coatings: plasma spraying. Hydroxylapatite targets were ablated at 0.9 J cm−2 using an ArF excimer laser (193 nm) at 20 Hz in order to investigate the ablation rate of hydroxylapatite in different atmospheres: water vapour, Ar and O2. The ablation rate was measured by profilometry for different pressures in a range of 15–80 Pa. The ablation rate depends on the backscattering of the ablated particles by the molecules of the gas, which produces different amounts of re-deposited material on the target surface for each gas. The ablation rate in a water vapour atmosphere presents a particular behaviour due to the formation of different calcium phosphate phases from the original hydroxylapatite under ArF excimer laser irradiation as compared those formed in other ambient gases.