ABSTRACT
Terahertz (THz) radiation, approximately defined in the 30−300μm range, lies in the region of the electromagnetic spectrum that is
often called the THz gap. The word “gap” originates from the lack of compact, solid-state, coherent radiation sources. However,
this problem has started to be seriously addressed with the
development of quantum cascade lasers (QCLs) operating in the
THz range [1]. These semiconductor-based sources-though still
limited in operating temperatures-hold the promise of being a
core component of practical THz systems devoted to spectroscopy,
sensing, and, more recently, imaging in a wide variety of application
areas (biomedical diagnostics, security, cultural heritage, quality
and process controls, etc.), mainly due to the fact that many
materials such as paper, plastics, and ceramics, which are opaque
at visible frequencies, are highly transmissive across the THz and
microwave ranges [2]. The other “THz gap,” which needs to be
overcome for imaging-oriented applications is the one concerning
detectors.
