Boundary conditions
The appropriate boundary conditions for light scattering at the interface
between two media are introduced in this section. These boundary
conditions for the diffuse radiance
at the slab boundaries must be specified before the
diffusion equation may be solved. They are appropriate for use with the
diffusion equation. The majority of this section treats the interface
between a scattering medium (tissue) and a non-scattering medium (e.g.,
air, glass, water-glass-air).
The simplest situation has matched indices of refraction across the
boundary and no incident diffuse light. This first case considered is
uncomplicated by either reflected light--caused by index of refraction
mismatching--or source terms arising from incident diffuse light. The
next case (index matching, diffuse light incident) illustrates how a
problem involving diffuse or Lambertian irradiance may be solved by
including an extra term in the boundary conditions. Boundaries between two
media with different indices of refraction are treated next, both with and
without diffuse incidence. Finally, boundaries between two scattering
media are considered. First with and then without index of refraction
matching. These cases are particularly important when light scattering in
multi-layered tissue is modelled.
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