Laser radiation tissue interaction.

Mechanisms of interaction between laser radiation and biological tissue are reviewed. Scattering and absorption determine the penetration of radiation into tissue; the heterogeneity of tissues prevents exact model calculations of in-depth energy deposition. The high irradiances, achievable with pulsed lasers, can induce nonlinear absorption, optical breakdown and plasma formation in tissues. Heat conduction and heat convection as well as the build-up and propagation of pressure transients damage tissue outside of the absorbing volume. The limitations to the validity of the first-order rate processes as a description for thermal tissue coagulation and the possibilities for novel photochemistry are discussed.