Prof Douglas J. Paul > Terahertz Research


The terahertz (THz or 10^12 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 5 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.

THz power

To the left is a graph showing output powers from a number of different sources in the literature up to June 2005. In particular we are investigating Si/SiGe quantum cascade lasers and Si/SiGe impurity lasers which are predicted to have benefits over presently available sources. The Si/SiGe QCLs should operate at higher temperatures than equivalent GaAs/AlGaAs THz QCLs due to the lack of polar optical phonon scattering but also the cheap and mature silicon technology should allow significantly cheaper devices to be realised.

The department in Glasgow has work on THz quantum cascade lasers, passive optical components using microfabrication and meta-material designs (electromagnetic bandgap designs), detector arrays and complete imaging systems. We have a number of collaborators including TeraView Ltd., Kodak U.K. and the University of Leeds.