Optics of slanted chiral sculptured thin films

Sculptured thin films (STFs) are unidirectionally nonhomogeneous, anisotropic nanomaterials comprising parallel nanowires of tailored morphology. The nanowire morphology of STFs is exploited to evoke remarkable optical phenomenons of technological interest. To couple the characteristic optical responses of volume gratings and diffraction gratings in the STF architecture, slanted chiral STFs are proposed and optically characterized in this thesis.; The objective of this thesis is to theoretically establish an optical framework for slanted chiral STFs. This objective is achieved by investigating the optical responses of slanted chiral STFs to several types of excitation sources, such as plane waves, optical beams, and dipoles. These studies would also help integrate slanted chiral STFs with semiconductor chips used in the electronics industry.; First, the response of slanted chiral STFs to plane waves is investigated by developing a robust numerical procedure involving the rigorous coupled-wave analysis. The prominent feature of the planewave response is the partial exhibition of the circular Bragg phenomenon in a nonspecular reflection mode and in its diminishment and even elimination by a Rayleigh-Wood anomaly.; Next, the optical response of a slanted chiral STF with a central twist defect is explored, numerically as well as analytically. Due to the twist defect, wave resonance occurs in a localized fashion in the Bragg regime. A remarkable crossover phenomenon is found in slanted chiral STFs for the localization of wave resonance: When the slanted chiral STF is relatively thin, a co-handed reflectance hole occurs in the Bragg regime; as the thickness increases, the co-handed reflectance hole diminishes to vanish eventually, and is replaced by a cross-handed transmittance hole. A coupled-wave theory is employed to derive an approximate but closed-form solution for axial wave propagation in chiral STFs. The crossover phenomenon can be harnessed for the design of ultra-narrowband optical filters.; Finally, the optical responses of slanted chiral STFs to both optical beams and dipolar radiations are examined, which are a step closer to practical applications. An optical beam is represented as an angular spectrum of plane waves, while dipolar radiation is formulated in terms of spectral dyadic Green functions. Lateral shifts of optical beams on reflection by slanted chiral STFs are computed and characterized, with emphasis on the Goos-Hanchen shift. Being comparable with the dimensions of nanomaterials, these lateral shifts are too important to be neglected in nanotechnology. The radiation patterns of Beltrami dipolar sources in the presence of slanted chiral STFs are presented, to elucidate the spatial signature of the circular Bragg phenomenon.; Potential applications of slanted chiral STFs are suggested in this thesis as optical beam-splitters and couplers, nanoband and sub-nanoband spectral-hole filters, and biosensors.