Routine generalized ellipsometry measurements at terahertz (THz) frequencies have become available only very recently, and we present and discuss the application to highly-ordered three-dimensional nanostructure thin films. Such nanostructure thin films are obtained from glancing angle deposition, and consist of slanted columnar structures with high spatial coherence. The slanted columnar thin films reveal strong birefringence due to electronic coupling and screening phenomena. Despite their extreme smallness compared with the THz wavelengThequivalent, slanted columnar nanostructure thin films can be used as sensors for dielectric fluids in transmission or reflection geometries, where measurements can be made through the back side of THz-transparent substrates. We describe an anisotropic biaxial effective medium dielectric function approach which comprises structural, geometrical and constituent fraction information, and which enables quantitative analysis of THz generalized ellipsometry measurements. We further describe a frequencydomain generalized ellipsometer setup which incorporates backward wave oscillator sources.
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