Abstract

Short-pulse laser ablation of soft biological tissues has a number of advantages as compared with long pulse (CW) regime that include: minor thermal damage to layers adjacent to the irradiated volume, higher efficiency and spectral selectivity. Mechanism of ablation upon confined stress conditions was determined. It is essential for realization of full potential precision of pulsed laser ablation applied in medical treatments. The following questions were answered: (1) ablation process is not driven by photodissociation of biopolymers, why ablation occurs at temperatures below 100 °C, (2) the major fraction of absorbed laser energy undergoes tissue heating, why energy' densely required for tissue removal is ten times less as compared with enthalpy of vaporization, (3) why the crater depth per pulse can never reach the penetration depth of light. The thermomechanical model of pulsed ablation is developed. Ablation of water containing media is found to include the following stages: instant heating of irradiated volume, sharp increase of pressure, formation of negative stress transient, cavitation by tensile wave, intense ejection of an irradiated substance by growing cavitation bubbles, collapse of cavitation bubbles with formation of a shock wave, spallation of tissue by this shock wave. Important role of tissue optical heterogeneity is revealed and studied.

© 1993 Optical Society of America