Conditions for circular polarisation retention in highly scattering media

We analyse conditions for circular polarisation retention in multiple scattering of light by disordered media. The effect of circular polarisation memory is shown to appear when the depolarisation cross section is much smaller than the transport cross section of elastic scattering. This situation occurs in media composed of large (compared to the wavelength of light) weakly refracting scatterers and of resonant Mie particles. Absorption in the medium is shown to result in a significant increase in the depolarisation length.