Creation of the heat source The heat source is induced by the conversion of the laser light into heat. The optical reflection determiens the proportion of the beam which will effectively penetrate the tissue. However, for wavelengths longer than the visible range, the reflection tends to diminish considerably. The diffusion plays an important role in the spatial distribution of the energy absorbed. The absorption depends on the wavelength - chromophore combination .
Most organic molecules have high absorption in the ultra-violet range.
Then, in the medium and far infra-red, it is the water which absorbs the light intensively, which therefore only has very superficial effects. The conduction can be considered as an energy transfer by interaction of the tissue particles. The denaturing of the tissue is the final result of the thermal action of the tissue. The knowwledge of the kinetics of this transformation is necessary in order to describe the denaturing process. The kinetics depend on the temperature of the tissues, the duration of the heating and the sensitivity of the tissue to thermal aggression.