Etch rate and spectroscopic ablation studies of Er:YAG laser-irradiated dentine

The interaction of a 200-mus Er:YAG laser at 2.94 mum with human molar dentine has been studied by ablation depth rate measurements as well as time-resolved and optical multichannel analyzer emission spectroscopy. Ablation rates indicate a threshold fluence of ~5.2 J cm(-2) for significant material removal with a low-fluence (<20 J cm(-2)) effective optical absorption coefficient of ~700 cm(-1). Deviation from a Beer's law dependence is significant in the range ~20 to ~60 J cm(-2) and indicates a maximum effective plume absorption of ~1200 cm(-1) at ~40 J cm(-2), coinciding with the appearance of strong line and broadband optical emission in the visible region. Time-of-flight emission measurements yield maximum species-resolved ablation velocities of up to ~1.2 x 10(6) cm s(-1), enabling calculation of plasma temperatures. The results suggest that etch-rate characteristics are driven by changes in plume absorption dynamics, which have a strong dependency on incident laser fluence.