ABSTRACT
The terahertz (THz) frequency range, lying between the microwave and the midinfrared frequencies (~0.3-10 THz), remains one of the least-developed regions in the electromagnetic spectrum. THz radiation has, however, proven potentially widespread and important applications in, for example, spectroscopy, heterodyne detection, imaging, and communications [1]. In many of these applications, suitable high-power coherent THz sources with low beam divergence and single-mode operation are highly desirable. Therefore, much emphasis has been placed on the development of new and appropriate THz sources, and in particular with a focus on the development of electrically pumped, semiconductor-based light sources that can be mass-produced. A breakthrough occurred in 2002, when the rst THz quantum cascade lasers (QCLs) were demonstrated [2].
