Theory of angular selective transmittance in oblique columnar thin films containing metal and voids

The transmittance T and reflectance R of s- and p-polarized light, incident at various angles onto thin films which contain metal and voids in an oblique columnar structure, are analyzed using suitably modified thin film equations. Columnar aluminum is treated for various column angles in uniaxial and biaxial models to demonstrate that the model can predict the novel features found in recent experiments. Dielectric constants from quasistatic effective medium theory are used. The p-wave transmittance can be very asymmetric as incident angle theta varies about the normal, but R(p), R(s), and T(s) are symmetric. It is differences in the forward and reverse imaginary part of the complex p-wave phase shift for each theta that causes T(p) to be asymmetric. This difference leads to a modification to the standard thin film equations, or transfer matrix elements, which do not vanish when intensity amplitudes are calculated. Angular selective transmittance of luminous and solar radiation then becomes possible, which is important for several energy related applications.