Role of group velocity delay in Faraday rotation in a multilayer polymer lattice

We measure and model the spectral dependence of Faraday rotation in one-dimensional lattice structures composed of co-extruded alternating polymer layers of polymethylmethacrylate and polystyrene. We develop a theory that shows that the net Faraday rotation in a symmetric multilayer system is determined not by the total thickness of the constituent materials but by the time spent in each constituent material as measured by the overall group velocity delay of the structure and the relative energy distribution per material. We compare measured and computed Faraday rotation spectra for these films to theoretical predictions, taking into account ellipticity as well as layer thickness variations and finite spectral width detection. To measure rotations of these thin, nonmagnetic, weak Faraday rotators, we constructed and optimized an apparatus capable of measuring broadband Faraday rotation spectra at 0.001 degrees resolution for rotation angles as small as 0.002 degrees. (C) 2012 Optical Society of America