Terahertz radiation induced by coherent phonon generation via impulsive stimulated Raman scattering in paratellurite

摘要

We report on the observation of terahertz radiation in a non-centrosymmetricinsulating oxide, paratellurite ($\alpha$-TeO$_2$) by irradiation of afemtosecond laser pulse at room temperature. In the power spectrum of theterahertz radiation, an intensity fringe pattern with a period of $\sim$ 0.25THz shows up below 3 THz. It can be reproduced by taking into account theeffective generation length for the terahertz radiation with a poorphase-matching condition. In addition, a temporal oscillation component appearsin the radiated terahertz wave with a frequency of $\sim$ 3.71 THz, which is ingood agreement with the center frequency of the Raman active longitudinaloptical (LO) $E$ mode. On the basis of comprehensive polarized optical andRaman spectroscopic studies, we explain the generation mechanism of thetemporal oscillation component in terms of the coherent phonon generation viaimpulsive stimulated Raman scattering.