Abstract: y, we have shown that coherent lattice vibration can be induced and subsequently detected in certain semimetals and semiconductors (e.g. Bi, Sb, Te, Ti$-2$/O$-3$/) using short pulses of optical light. The time-resolved optical pump-probe data show in each case that only totally symmetric lattice modes (i.e. A$-1$/ symmetry) are coherently excited, even though other symmetry modes of comparable Raman cross-section exist. Careful measurement of the coherent photon phase reveals that the excitation mechanism for coherent phonons is related to a pump- induced shift in the ion equilibrium configuration in these materials. Of particular interest in these experiments are the magnitudes of the observed reflectivity modulations. Implications of lattice modulations are discussed as well as the validity of employing the equilibrium calibration in the transient regime.!0
展开▼
