Terahertz time-domain spectroscopic study of ferroelectrics

A new compact instrument of terahertz time-domain spectrometry (THz-TDS) has been developed to expand the THz-TDS adaptation for far-infrared quantitative measurements on functional materials. THz-TDS enables us to measure simultaneously the spectral amplitude and phase shift in the far-infrared region between 1 and 100 cm^-1 so that the real and imaginary parts of complex dielectric function can be estimated independently without the Kramers-Kronig analysis. The details of the new compact instrument of THz-TDS are introduced, and the complex dielectric function and the phonon-polariton dispersion relation of ferroelectric Li₂Ge₇O₁₅ at 295 K are estimated and they are elucidated in terms of the Kurosawa formula.