The terahertz (THz or 1012 Hz) is the part of the electromagnetic spectrum where most molecules have rotational and vibrational absorption modes and therefore is a rich area for molecular spectroscopy. The frequency range is also termed the far-infrared but the terahertz term was originally used for the region between photonic devices and electronic transit-time devices where few practical sources of radiation were previously available, termed the THz gap (roughly 200 GHz to 10 THz - or 30 µm to 1.5 mm wavelength). In the last 10 years this situation has changed significantly and there are many THz sources available with differing power, bandwidth and operating temperatures (see below). The frequency range is particularly interesting for medical and security imaging and spectroscopy as the radiation is non-ionising and hence is far safer than X-ray or gamma camera techniques.
We are working on producing a quantum cascade laser using Ge and SiGe epilayers grown on top of silicon substrates. As QCLs are unipolar, gain can be produced even in indirect bandgap material, unlike any interband laser.
We are a partner in the EC project Far-infrared Laser using Assembled Silicon Heterostructures (FLASH) led by Roma Tre with ETH Zurich, IHP and Nextnano.