Laser based surface treatment of bioactive glass: Dependence on pulsed laser ablation

Abstract

Experimental results and theoretical simulation of material ablation on nanosecond Nd:YAG laser irradiation of bioactive glass targets, is presented. The process of pulsed laser ablation critically affects both, laser based surface modification and pulsed laser deposition (PLD) of bioactive glass (BG). A thermal model based theoretical simulation has been carried out describing heat-transport, melting and vaporization of a laser irradiated BG target under near-threshold ablation conditions. Calculated mass ablation rate per laser pulse has been compared with our experimental observations over the average laser fluence of 0.5J/cm2 to 6J/cm2. With increasing laser fluence, possibility of material ablation approaching phase explosion has been discussed by comparing the calculated maximum temperature reached by the laser irradiated target and the estimated thermodynamic critical temperature for BG. Our investigations indicate that with average laser fluence restricted to ∼5 J/cm2 material ablation occurs largely via normal vaporization ensuring deposition of an uniform, homogeneous BG coating through PLD. Target surface temperatures estimated from our calculations also suggest that laser based surface modification of BG can be reproducibly carried out without causing target crystallization and surface damage through crater formation for irradiating laser fluence in the region of ∼ 5J/cm2.