Strong optical phonon mode of natural seraphinite probed by terahertz time-domain spectroscopy

The natural seraphinite has the optical phonon modes in the frequency range from 0.1 to 2 THz. The observed absorption modes at 0.8, 1.2, and 0.96 THz are understood as infrared active phonon modes of A_u(z) and B_u(x, y) symmetries, respectively. The 0.96 THz mode is, in particular, strong and narrow comparable to the reported 0.53 THz mode in a-lactose monohydrate. Experiments carried out by THz time-domain spectroscopy shows a good agreement with theoretical analysis based on the phonon-polarition dispersion relation.