Abstract
ABSTRACTThe recent progress of Terahertz Time-Domain Spectroscopy (THz-TDS) using a coherent terahertz radiation enables the accurate and reliable measurements of dielectric properties in comparison with the traditional far-infrared spectroscopy using an incoherent light source. The applications of the broadband THz-TDS to infrared active soft modes and phonon-polaritons in ferroelectrics were reviewed. The broadband THz-TDS is a powerful tool to determine the real and imaginary parts of a complex dielectric constant by the transmission and reflection measurements in the frequency range between 0.2 and 6.5 THz. The infrared active soft modes were clearly observed in quantum paraelectric SrTiO3, incipient ferroelectric BaZrO3, and improper ferroelectric β-Gd2(MoO4)3. THz-TDS enables to determine also the complex dispersion relations of phonon-polariton including the spatial decay of polariton. The polariton dispersions of Raman inactive soft mode of SrTiO3, the lowest-frequency modes of ferroelectric LiTaO3 and LiNbO3 were discussed.
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