Physical mechanisms of laser-induced shockwave lithotripsy with microsecond laser pulses

Abstract

Physical mechanisms of microsecond laser lithotripsy in the visible range are discussed. Theoretical model for the case ofstones which can be represented as a high-scattering low-absorption medium containing high-absorptive organic micropores is developed. The evolution of the state for such individual pore under the influence of laser radiation is described.Governing equations are derived and it was shown that there exists avalanche-like process of pore absorption increase due to the process of pyrocarbon generation. This generation is caused by the thermochemical dissociation of pore organic matter. Such effect leads to the increasing of laser pulse energy absorption and pressure front formation. This front may account for destruction of significant layer of the stone surface.Plasma can not flush under the conditions typical for described process. It starts play significant role only after primary stone destruction produced by proposed mechanism. Sharp increasing of stone absorption and modification of the destructed layer state may be considered as a good boost for the later effective plasma generation.