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 observing the acoustic folded branches, and by analyzing the involved phonon modes, it is possible to extract accurate structural information about these devices, which is essential for their design and performance.