Investigation of vibrational modes of SiO2 and LaBGeO5 using a frequency-tunable terahertz source

We have investigated and compared vibrational modes of SiO2 and LaBGeO5 in the glass and crystalline phases based on terahertz (THz) spectroscopy. This is made possible by frequency-tuning a THz source developed by us recently. The THz absorption spectra are significantly different between the two phases of the same composition. In particular, we have identified the transition peak at 78.0 μm for the SiO2 crystal (i.e. quartz). Moreover, we have observed an evidence for a boson peak in the spectrum for LaBGeO5 glass.