  We develop a model of full-field optical coherence tomography (FF-OCT) that
includes a description of partial temporal and spatial coherence, together with
a mean-field scattering theory going beyond the Born approximation. Based on
explicit expressions of the FF-OCT signal, we discuss essential features of
FF-OCT imaging, such as the influence of partial coherence on the optical
transfer function, and on the decay of the signal with depth that is captured
by the model. We derive the conditions under which the spatially averaged
signal exhibits a pure exponential decay with depth, providing a clear frame
for the use of the Beer-Lambert law for quantitative measurements of the
extinction length in scattering media.
