Role of tissue optics and pulse duration on tissue effects during high-power laser irradiation.

The primary zone of deposition of optical energy is called here the optical zone. The tissue absorption, tissue scattering, laser-beam diameter, or size of pigmented structures can specify the size of the optical zone. The initial optical zone may be altered by the formation of char during high-irradiance laser exposure, and a spectrum of char absorbance is presented. The relationship between the optical zone and the pulse duration specifies the type of laser-tissue interaction that may occur. Short laser pulses can confine thermal energy and/or stress energy within the optical zone, which maximizes photothermal and photomechanical mechanisms of interaction.