Capability of broadband solid-state room-temperature coherent sources in the terahertz range

Recent outstanding results achieved with the HIFI instrument on board the Herschel Space Telescope are driving a new generation of high-resolution coherent detectors in the terahertz range, not only for astrophysics but also for planetary science and Earth science missions. Schottky based receivers in the THz range and advanced receiver topologies such as compact arrays and side-band-separation require a new generation of THz sources. In this article, the state-of-the-art of terahertz sources will be reviewed and novel techniques being used to push the limits of the technology will be discussed. The focus will be on the most commonly used frequency multiplied sources, which are broadband, tunable, frequency agile, temperature stable and able to operate at room-temperature.