2. Optical mechanisms

Before detailing the various effects obtained, this article will describe the optical phenomena involved in light-biological tissue interaction, as these condition the final action. Biological tissues are complex, highly heterogeneous media, composed of scattering and absorbing structures and organelles. Their optical properties not only vary from one tissue to another, but can also vary within the same tissue due to local inhomogeneities. As with any material medium, light-tissue interaction involves three different phenomena: reflection, absorption and scattering .