Time-domain depolarization of waves retroreflected from dense colloidal media

We report on depolarization measurements of femtosecond pulses retroreflected from dense suspensions of silica microspheres with solid loads increasing from 5% to 54%. Backscattered pulse shapes compare well with predictions of the diffusion theory for all volume fractions, and the inferred values of the transport mean free path agree with independent measurements of enhanced backscattering. The measured degree of polarization decays exponentially with temporal rates that scale with the solid load. It is newly found that, for all solid loads, depolarization sets in for path lengths longer than approximately five transport mean free paths.