Coherent Control of LO-Phonon Dynamics in Opaque Semiconductors by Femtosecond Laser Pulses

Abstract

Coherent longitudinal optical phonons are generated via ultrafast screening of GaAs surface-space-charge fields by free carriers excited with femtosecond laser pulses. The coherent phonons are observed in a pump probe experiment through anisotropic changes in the refractive index. Since the electro-optic observation of phonons in the time domain allows the determination of both the amplitude and the phase of coherent lattice vibrations, we are able to superpose two coherently excited phonon modes in a dual excitation experiment. By carefully adjusting the relative phase, we are able to accurately control the amplitude of the coherent vibrations from resonant enhancement to total extinction. The experiment demonstrates the possibility of a coherent control of the lattice dynamics in solid-state materials at room temperature.