Far-Infrared Ferroelectric Soft Phonon-Polariton Probed by THz Time Domain Spectroscopy

This paper reports the pioneering application of the terahertz time domain spectroscopy to ferroelectric bismuth titanate and lithium niobate crystals. By the use of the THz coherent radiation both the intensity and phase of transmittance have been measured accurately. The complex dielectic constant is determined by Fourier transformation of time domain transmission amplitude and phase in the frequency region from 3 cm m 1 to 60 cm m 1 . The polariton-dispersion curves were determined by the phase delay as a function of THz radiation frequency. The obtained lowest polariton limit of 3 cm m 1 is far below the limit of the Raman scattering technique.

Keywords:

• Thz-TDS
• Phonon-polariton
• Complex Dielectric Constants
• Bismuth Titanate
• Lithium Niobate