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.
S. L. Jacques, "Role of tissue optics and pulse duration on tissue effects during high-power laser irradiation," Appl. Opt.,32, 2447-2454 (1993).