Observation of longitudinal optical-transverse optical splitting for E-symmetry phonons in Te by coherent phonon spectroscopy

We report on the fermosecond time-resolved detection of coherent phonons in single-crystal tellurium. For different crystallographic faces a detection scheme is employed which is sensitive to the anisotropic part of the Raman tensor. In this scheme we observe all three Raman allowed phonons, i.e. one of A(1) and two of E symmetry. Furthermore, for both doubly degenerate E-symmetry modes obtained from different crystallographic faces, longitudinal optical-transverse optical splitting is observed. In addition, we show that even in the low fluence regime the frequency of the fully symmetric phonon in Te is chirped and that it demonstrates an anomalous dependence on the pump fluence.