Investigation of coherent acoustic phonons in THz quantum cascade laser structures

Coherent zone folded acoustic phonons in terahertz quantum cascade laser (QCL) structures [1] are investigated by high-speed asynchronous optical sampling [2]. This method is based on two Ti:sapphire lasers with repetition rates of ∼1 GHz respectively. The time delay between pump and probe pulse is achieved by an offset in repetition rate of 5kHz. This allows for fast scanning times without moving mechanical parts [3].