Coherent Control of Terahertz Wave from Coherent Longitudinal Optical Phonon in a GaAs/AlAs Multiple-Quantum-Well Structure

We report on the coherent control of terahertz (THz) waves emitted from coherent longitudinal optical (LO) phonons in a GaAs/AlAs multiple-quantum-well structure at room temperature using two-pulse excitation. When the time difference between the first pump pulse and second weak control pulse is increased, the intensity of THz waves from the coherent phonons is cancelled and enhanced by the control pulse, and the phase of THz waves shows periodic changes accompanied by a phase jump. The time-difference dependences of the intensity and phase of THz waves are explained in terms of the superposition of two coherent oscillations.