General assumptions
This section outlines the fundamental assumptions made throughout this
dissertation. First, the distribution of light is assumed static with time, and
consequently, both optical properties which change and irradiance times shorter
than about one nanosecond are excluded. Second, all media are assumed to have
homogeneous optical properties. This restriction may be relaxed somewhat in
the models presented, but all results in this dissertation are for strictly optically
homogeneous media.
A third assumption is that the tissue geometry may be approximated by
an infinite plane-parallel slab of finite thickness. Such a shape allows
generalization to layered tissues or extension to an infinitely thick tissue. This
assumption requires that the beam width be smaller than the width of the tissue.
The tissue is assumed to have a uniform index of refraction. This ensures
that light will travel in a straight line until it is scattered or absorbed. The
boundaries are assumed smooth and to reflect specularly according to Fresnel's
law. The last assumption is that the polarization of light may be ignored.
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