Interaction Mechanisms

Abstract

The variety of interaction mechanisms that may occur when applying laser light to biological tissue is manifold. Specific tissue characteristics as well as laser parameters contribute to this diversity. Most important among optical tissue properties are the coefficients of reflection, absorption, and scattering which were discussed in detail in the preceding chapter. Together, they determine the total transmission of the tissue at a certain wavelength. Thermal tissue properties — such as heat conduction and heat capacity — will be added in this chapter. On the other hand, the following parameters are given by the laser radiation itself: wavelength, exposure time, applied energy, focal spot size, energy density, and power density¹. Among these, the exposure time is a very crucial parameter when selecting a certain type of interaction, as we will find later on.

In the literature, the terms used for radiometric parameters such as fluence, irradiance, intensity, and energy dose are often somewhat confusing. Throughout this book, the following agreements are met: power is expressed in units of W, energy in units of J, the synonyms power density, intensity, and irradiance in units of W/cm², the synonyms energy density, fluence, and radiant exposure in units of J/cm², and energy dose in units of J/cm³ (see also the Appendix).