Optical beam propagation in soft anisotropic biological tissues

We introduce a geometrical anisotropy parameter in the power spectrum of soft biological tissue and study its effects on the statistics of light beams propagating in it, in addition to the effects of other parameters, such as the refractive index variance, the slope of the power spectrum, and the inner/outer scales of the tissue. In particular, we discuss the behavior of widely known Gaussian Schell-model beams, and the theory can be readily adapted to other beams. Our results based on the extended Huygens-Fresnel integral indicate that the spectral density of the beam starts acquiring an elliptical profile at distances on the order of millimeters from the plane of incidence. We also find that, since the inner scale of a typical bio-tissue is smaller than the wavelength of light, the beams become incoherent at submicron distances and, hence, the effects of the source degree of coherence of the beam are not practically detectable. Our results may be applicable to light propagation in inherently anisotropic biological tissues, such as the ones containing fibers, or isotropic tissues under mechanical stresses.