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Liquid crystals are candidate materials for optical devices operating in the Terahertz (THz) frequency region of the electromagnetic spectrum. Proposed devices include THz phase shifters and THz quarter wave plates. To assist in designing for these applications, the fundamental properties of the materials should be determined. Fundamental optical properties to be determined over the frequency range of interest are the refractive index n and the absorption coefficient α. According to the orientation of the liquid crystals relative to the polarisation of the light field, ordinary and extraordinary values for the refractive index may be distinguished. In early work, employing time-domain spectroscopy, a rise in both n o and n e with optical frequency in the THz region was reported. Later work, employing two-colour generation of THz radiation, indicated the values of n o and n e were both relatively constant in the THz region. We have now made measurements of the two common nematic liquid crystals K15 and E7 using time-domain THz spectroscopy and confirm that n o and n e show little change over the spectral region 0.15 to 1 THz.

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