Optical control of polarized terahertz waves using dye-doped nematic liquid crystals

We propose an optically tunable terahertz (THz) polarization converter based on use of a dye-doped nematic liquid crystal (LC). The dye-doped LC exhibits a photothermally-induced nematic-isotropic phase transition under irradiation by a laser beam with a wavelength that lies within the absorption band of the dye. We investigate the transmission spectra and the polarization-conversion properties of the dye-doped LC cell with twisted alignment using THz time-domain spectroscopy. The polarization state of a THz wave transmitted through the proposed dye-doped LC cell can be controlled using the laser beam irradiation based on the photothermal effect. The experimental results also demonstrate that optical control of this dye-doped LC cell offers an advantage in terms of response speed when compared with voltage-based control of LC cells via their electrodes. The dye-doped LC proposed in this study presents the possibility that a variety of LC-based THz elements with optical tunability may be realized.