Spectral investigation of nematic liquid crystals with high optical anisotropy at THz frequency range

Liquid crystals (LCs) with high optical anisotropy are very desirable for different applications in devices, such as filters, phase shifters, or phase gratings [T. Gobel, P. Meissner, A. Gaebler, M. Koeberle, S. Mueller, and R. Jakoby, Dual-Frequency Switching Liquid Crystal Based Tunable THz Filter, CLEO, Baltimore, MD, 2009; C.-Y. Chen, T.-R. Tsai, C.-L. Pan, and R.-P. Pan, Room temperature terahertz phase shifter based on magnetically controlled birefringence in liquid crystals, Appl. Phys. Lett. 83 (2003), pp. 4497-4499; and C.-J. Lin, C.-H. Lin, Y.-T. Li, R.-P. Pan, and C.-L. Pan, Electrically controlled liquid crystal phase grating for terahertz waves, IEEE Photon. Technol. Lett. 21 (2009), pp. 730-732]. We present spectral studies of LCs with large optical anisotropy in the range from 0.3 to 3 THz. Nematic LC mixtures which have Delta n > 0.30 for visible frequency range, i.e., 1825 (Delta n = 0.42 at 633 nm) were measured. Properties of LC materials like birefringence, absorption coefficients, and refractive indices for ordinary and extraordinary polarization in THz range were obtained. Orientation of LC was done by a high electric field. Measurements were performed using a TDS spectra 3000 spectrometer.