Generation of coherent optical phonons in ZnO using femtosecond lasers

Abstract

We observed the high- and low-frequency E-2 optical phonon modes of wurtzite ZnO. Their dephasing times of 1.75 ps, 29.2 ps were obtained at room temperature. We tested polarization dependence of the coherent phonon excitation and the behavior is fully consistent with the selection of the Impulsive Stimulated Raman Scattering(ISRS), identifying the generation mechanism. Also, we studied the relations between the optical phonon intensity and the pulse width of the transform-limited pump pulse. Our experimental results fully correspond to our simple models based on the ISRS, showing that for efficient excitation of higher energy phonon modes, shorter pulses are needed.