Birefringence of nanoporous alumina: experiment vs. theory

We report on experimental and theoretical investigation of birefringence of free-standing nanoporous anodic alumina membranes in the optical range. The value of birefringence is analyzed for the samples with different porosities by measuring polarization dependent transmission spectra at different angles of incidence. The experimental data are compared to the results of birefringence simulations in accordance with three simulation approaches: modified Bruggeman effective-medium approximation, Boundary conditions model, plane-wave expansion method. It is both experimentally and theoretically shown that birefringence value increases with porosity increasing in the low porosity region. The porous alumina samples under investigation possess greatest value of birefringence (0.062) up to date.