Ellipsoid-based model of structure-response relationships for chiral sculptured thin films

Dielectric versions of helicoidal bianisotropic mediums (HBMs) have been realized recently as chiral sculptured thin films (STFs). With a view to understanding their structure-response relationships, these STFs are modeled as periodically arranged stacks of dielectric ellipsoidal inclusions in air. The inclusions are assumed to be randomly dispersed and similarly oriented in each stack, and the Bruggeman formalism is adopted for local homogenization. The constitutive properties are examined as functions of inclusion shape, volume fraction, and orientation angles. Optical signatures of the modeled thin-film HBM (TFHBM) layers, assumed axially excited, are calculated after solving a boundary value problem. Several conclusions drawn from the calculated spectrums of co- and cross-polarized reflectances and transmittances, true and apparent circular dichroisms, true and apparent linear dichroisms, ellipticity transformation, and optical rotation are presented.