Nematic liquid crystals as a new challenge for radiative transfer

Radiative transfer has been studied for almost a century, but only recently have effects of broken symmetry in the diffusion of light been systematically studied. Familiar concepts such as the mean free path and the diffusion constant must be generalized. Nematic liquid crystals provide a realistic complex system in which the new concepts are relevant. Thermal fluctuations of the local optical axis generate a weak but very specific and anisotropic light scattering and can even be long range. In addition, two different modes of electromagnetic propagation exist, with different polarization, and with different speeds, that couple in multiple scattering. It becomes a challenge to describe optical phenomena such as birefringence, interference, polarization, and intensity fluctuations under such conditions. In this review, the authors first describe the interesting phenomena in radiative transfer in complex anisotropic media and nematic liquid crystals. They then develop the systematic theory of transport starting from the fundamental equations and going through a Green’s-function formulation.