Description:
<jats:p>The complex dielectric constants of congruent LiNbO<jats:sub>3</jats:sub> and LiTaO<jats:sub>3</jats:sub> single crystals in a THz frequency region have been determined directly by using broadband terahertz time-domain spectroscopy (THz-TDS) with reflection configuration. We have successfully extracted the accurate complex dielectric constants by using corrected phase information derived from the transmission measurement results. The lowest <jats:italic>E</jats:italic>(TO1) phonon modes of both crystals have been observed clearly. On the other hand, additional bands at approximately 2.5 THz below the lowest <jats:italic>A</jats:italic>
<jats:sub>1</jats:sub>(TO1) mode frequency have been observed. These bands have also been reported by Raman and hyper-Raman spectroscopy and attributed to intrinsic defects in congruent crystals. According to the experimental results that these additional bands were observed at almost the same frequency on Raman, hyper-Raman, and THz-TDS, these bands are suggested to be assigned as a first-order scattering process.</jats:p>