COHERENCE AND POLARIZATION OF LIGHT PROPAGATING THROUGH SCATTERING MEDIA AND BIOLOGICAL TISSUES

The degree of polarization of light propagating through scattering med ia was measured as a function of the sample thickness in a Mach-Zehnde r interferometer at a wavelength of lambda = 633 nm. For polystyrene m icrospheres of diameters 200, 430, and 940 nm, depolarization began to appear for thicknesses larger than 23, 19, and 15 scattering mean fre e paths (SMFP's), respectively, where the coherently detected scattere d component dominates the ballistic component. For large particles (94 0 nm) the initial polarization survived partially in the scattering re gime and progressively vanished up to the detection limit of our setup . This phenomenon was similarly observed in diluted blood from 12.5 to 280 SMFP's. Beyond this thickness the fluctuating parallel and crosse d components of polarization became random. A dual-channel interferome ter allowed us to detect simultaneously the low-frequency fluctuations of both polarized components through a few millimeters in liver tissu e. (C) 1998 Optical Society of America OCIS codes: 040.2840, 170.3660, 170.4580, 260.5430.