Terahertz time-domain spectroscopy of low-energy excitations in glasses

The low-energy excitations in glasses were studied by the terahertz time-domain spectroscopy (THz-TDS). The coherent THz radiation by a femto-second pulse laser enables the determination of the real and the imaginary parts of complex dielectric constants in the frequency range between 0.3 and 2.4 THz. The complex dielectric spectra of glasses clearly show the existence of broad low-energy excitations called boson peaks.