Mid-infrared laser ablation of a hard biocomposite material: mechanistic studies of pulse duration and interface effects

Cortical bone is a hard biocomposite material comprising protein, mineral crystal and water. We have studied mid-infrared laser ablation of bovine cortical bone using a free-electron laser (FEL) and an Er:YAG laser at a wavelength of 2.94 μm, comparing pulse duration and interface effects. Bovine bone samples were irradiated both in air and while irrigating with biologically inert perfluorocarbon. The perfluorocarbon dissipates heat and acoustical stress, and at the lowest scanning speeds, appears to inhibit carbonization. The ablation efficiency and etch rates are critically dependent on scanning speed, laser fluence, and the molecular weight and depth of the perfluorocarbon. The observed phenomenology is consistent with an explosive vaporization as the principal mechanism of ablation; in addition, there may be nonlinear absorption effects.