Time-resolved THz phonon spectroscopy in semiconductors

We present our recent application of the coherent mid-infrared measurement technique for phonon spectroscopy. We investigate the dynamics of phonons interacting with THz radiation. First, we excite coherent LO phonons using ultrashort near-infrared laser pulse. The THz radiation field emitted by coherent phonons is detected in the Fresnel geometry under different excitation conditions in different semiconductors. The results are discussed in terms of the dynamics and amplitude. We discuss results in different samples, i.e., semi-isolating and doped, under different optical excitation conditions. Furthermore we use coherent time-domain optics to study dielectric response dynamics in the reststrahl band. By analyzing the time-domain THz field reflectivity near the phonon frequencies of materials we demonstrate observation of a quantum kinetic behavior of the lattice dielectric response in a simple coherent optics scheme.