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The authors present terahertz time-domain spectroscopy (TDS) measurements on injection molded liquid crystalline polymers (LCPs). Pure LCP yields a strong birefringence of Δn=0.2. They find that the direction of the optical axis varies within the injection molded sample. By terahertz (polarization) imaging domains of certain directions of the optical axis could be observed. These strongly depend on the mold geometry. Since the alignment of particles and rodlike polymer molecules tend to follow the melt flow during injection molding, terahertz TDS can be used to analyze injection molded LCP parts and control the process performance.

Liquid crystals represent a very interesting material system but their properties in the THz range have not been extensively investigated yet. In this paper we investigate the THz properties of four liquid crystals from the CB family (5CB, 6CB, 7CB and 8CB). In addition to absolute refractive indices and absorption coefficients we present accurate birefringence measurements for different electric fields and temperatures.

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The authors present experimental results on photonic crystals in the subterahertz range for fluid-sensing applications. Using a standard machining process, a two-dimensional photonic crystal consisting of a triangular array of air holes in the dielectric medium was produced. The insertion of fluids with different refractive indices into the active region affects the transmission profile in the stop band. The experiment agrees well with theoretical calculations.