Optical methods utilize different types of light-matter interactions to provide structural, morphological, and biochemical information.
Penetration Depth is a measure of how deep light can penetrate into a material. It will depend on the absorption and scattering properties of the biological specimens.
When light falls onto a material sample, there is a small number of distinct interactions that typically take place. The nature of these interactions depends upon the wavelength of light and the structure and composition of the material. The absorption and scattering coefficients represent the overall attenuation of the light passing through the material. The attenuation causes an exponential degradation of the incident intensity with depth.
As light interacts with small structures of varying refractive index, it is angularly redistributed, or scattered. Scattering depends on the structure of a tissue, for example, the density the cells, the size of nuclei, the the status of hydration in the tissue, etc.
Absorption of light can provide information of the chemical composition of a tissue and can provide information such as tissue oxygenation, oxygen consumption, blood hemodynamic etc. Major tissue absorbers include: Hemoglobin, lipids, melanin, water, proteins.