We performed the broadband terahertz time-domain spectroscopy on archaeological Baltic amber at 40 million years old. We determined the real and imaginary parts of the complex dielectric constants in the frequency range from 0.2 to 6.5 THz. The imaginary part of the complex dielectric constants showed a broad peak at 1.51 THz and a small peak at 4.0 THz. A boson peak, which is the characteristic low energy excitation of a glassy state, was not observed above 0.2 THz even in low temperatures.
International Letters of Chemistry, Physics and Astronomy (Volume 62)
T. Sasaki et al., "Broadband Terahertz Time-Domain Spectroscopy of Archaeological Baltic Amber", International Letters of Chemistry, Physics and Astronomy, Vol. 62, pp. 29-33, 2015