Observation of Zone-Folded Acoustic Phonons in Terahertz Quantum Cascade Lasers using Picosecond Ultrasonics

We have investigated the time-resolved vibrational properties of terahertz quantum cascade lasers by means of ultra-fast laser spectroscopy. By the observation of the acoustic folded branches, and by analyzing the involved phonon modes it is possible to extract accurate structural information of these devices, which are essential for their design and performance.