THz time-domain spectroscopy of THz quantum cascade lasers

Summary form only given. We have combined few-cycle THz spectroscopy with quantum cascade laser (QCL) technology. This combination allows to perform unique THz time-domain measurements of THz-QCLs. By coupling the few-cycle THz pulse into the waveguide of the QCL, the processes within the active zone can be probed. This gives direct information regarding the energy, dynamics and coherence of transitions in the QCL structure.