The Effect of Laser Parameters on the Zone of Thermal Injury Produced by Laser Ablation of Biological Tissue

A thermal model to predict the effect of laser parameters on the zone of thermal injury produced by laser ablation of biological tissue is presented. The model suggests that the Pe´cle`t number based on the optical penetration depth of laser radiation is the key parameter in determining the resulting zone of thermal injury. We show that the zone of thermal injury is minimized for Pe´cle`t numbers greater than one since the transport of energy via conduction beyond the ablation front is minimized. We also show that for Pe´cle`t numbers less than one, larger zones of thermal damage are unavoidable regardless of the laser pulse duration. The predictions of the model are compared with data available in the literature. Deviations between the model predictions and published data are discussed and the potential effects of the model assumptions, optical scattering, pyrolysis, temporal pulse shape, pulse duration, irradiance and pulse repetition rate are explored.