Effects of rough interfaces on a converging laser beam propagating in a skin tissue phantom

Light propagation in a turbid medium such as the skin tissue depends on both the bulk optical properties and the profiles of the interfaces where mismatch in the refractive index occurs. In this paper we present recent results of investigations on the light distribution inside a human skin tissue phantom for an incident converging laser beam and its dependence on the roughness of the interfaces. The human skin tissue is modeled by a two-layer structure with a thin layer of epidermis on top of the dermal layer. Within each layer, the tissue is considered macroscopically homogeneous and the two interfaces, between ambient medium, epidermis and dermis, are treated as random rough surfaces. The distribution of laser light with wavelength near 1 micrometers in the tissue phantom is considered using a recently developed method of Monte Carlo simulation. The dependence of the light distribution on the surface roughness and index mismatch are presented, and their relevance to the possible laser surgery under skin surface and the measurements of optical properties of the skin tissues is discussed.