Local inclination angle: A key structural factor in emission from chiral sculptured thin films

Sculptured thin films (STFs) are unidirectionally nonhomogeneous, anisotropic, porous, nanoengineered materials possessing morphological features of optically significant dimensions. Light emission efficiencies of chiral STFs are examined to establish the role of a key structural factor: the local inclination angle χ of the morphology. The centrality of its so-called pseudo-isotropic value χ^pi is identified. When the source configuration has the same handedness as the chiral STF, the emission spectrum is spread over the Bragg regime if χ is in the neighborhood of χ^pi; otherwise, the emission spectrum is highly localized in the short-wavelength (resp. long-wavelength) vicinity of the Bragg regime for χ>χ^pi (resp. χ<χ^pi). In contrast, the emission spectrum is spread over the entire Bragg regime for the contra-wound source configuration, regardless of the value of χ. High emission efficiencies require that χ be considerably less than χ^pi.