Polarization anisotropy of single crystal opal films

Single-crystal opal films have been prepared by the moving-meniscus and gravitational sedimentation methods. It has been found using conoscopy and spectroscopic ellipsometry that these photonic crystal opal films possess birefringence so that the optical indicatrix is a three-axial ellipsoid. The indicatrix axis Ng is directed along the crystal growth axis, the axis Nm lies in the film plane and is orthogonal to the axis Ng, and the axis Np coincides with the normal to the (111) crystallographic plane, which corresponds to the triclinic system of the crystal.