<title>Microsecond shockwave laser lithotripsy: analysis of induced absorption mechanisms</title>

Abstract

Theoretical model of microsecond shockwave laser lithotripsy is developed. The destroying stone is considered to be a medium with low absorption and high scattering which contains high-absorptive organic inclusions. Laser radiation penetrates deep into such type of media and bulk destruction processes may occur in its significant volume. The distribution of energy fluence in stone volume was found in diffusion approximation.The evolution ofstate for each individual inclusion was studied. It was shown that the organic matter thermochemical decomposition plays important role here. Such process leads to gas and high-absorption pyrocarbon generation. It produces sharp increasing of pore volume, cracks formation, and results shockwave generation. These processes change the state of illuminated stone layer -lead to the formation of highly absorptive loose composition. Such layer change -predesirtsction -produces conditions for the later effective transformation of laser energy. Some important dependencies for such processes were found both in simplified analytical form and numerically.Computer simulation for described model of microsecond laser lithotripsy was done with the parameters typical for ruby microsecond laser. Obtained results give the basis for the estimation of lithotripsy efficiency.

Nonlinear absorption: intraocular microsurgery and laser lithotripsy

“…The details of the process are, however, quite different. Plasma formation at clinically reasonable energy levels requires linear absorption of the stone, or of pigmented microinclusions (Berenberg et al 1994). It is therefore advantageous to choose a laser wavelength at which the absorption coefficient of the stone is high, usually in the short visible and UV wavelength range (Watson et al 1987, Nishioka et al 1987, Thomas et al 1988a.…”