Room-Temperature CW Widely-Tunable THz-Generating Laser

Abstract

The development of high-performance, room-temperature, continuous wave (CW), widely-tunable terahertz (THz) lasers has attracted considerable industrial interest and has shown great potential for applications in various fields ranging from THz spectroscopy and biomedical imaging to safety and security applications. Among the commonly used lasers, direct quantum cascade lasers are regarded as the most popular sources offering the highest-to-date wall-plug efficiency. However, such lasers generally require cryogenic cooling and suffer from the drawbacks in terms of the production complexity and the lack of broad tunability. On the other hand, high-performance laser sources based on semiconductor disk lasers (SDLs) and periodically-poled ferroelectric crystals can offer an access to new wavelengths not covered by available gain media, particularly in the THz spectral region. In this regard, vertical-external-cavity surface-emitting lasers (VECSELs), with remarkable output parameters, can allow the demonstration of highly-efficient THz emission in the 0.8 – 2 THz spectral window at room temperature based on difference frequency generation in advanced quasi-phase-matched crystals, such as periodically-poled lithium niobate (PPLN) and aperiodically-poled lithium niobate (aPPLN) crystals. In recent years, a few VECSEL-based THz sources, referred to as Terahertz-External-Cavity Surface-Emitting Lasers (TECSELs), have been demonstrated utilizing PPLN crystals [1–4], generating non-tunable multimode or, with certain efforts, even single-frequency THz signal.