Terahertz emission by difference frequency generation in nonlinear quantum cascade lasers

The THz regime is of high interest for commercial applications for which the newly emerged device class of THz DFG-QCLs is a promising candidate. This thesis improves current state of the art device concepts in two major aspects: active region design and waveguide configuration for THz extraction. The active region design is optimized to a single period design, which simultaneously provides optical gain and a nonlinear susceptibility for nonlinear THz generation. The novel waveguide configuration allows for vertical extraction of the THz mode, breaking previous limits of prevailing device concepts.