360° Image Courtesy of Dan Axson, Technology Enhanced Learning (TEL), University of Sussex.

Terahertz (THz) radiation is simply a form of electromagnetic radiation, whose frequency lies in the range of ~0.3-10THz. This region of frequencies is often called the "Terahertz gap" as up until recently there has been no efficient method for generating and detecting light with this specific frequency. The THz gap lies between Infrared light and microwaves and is the bridge that connects optical technologies with conventional electronics. The THz region has become very active since the discovery of a technique to measure the exact temporal evolution of the electric field through electro-optic sampling. The technique combines an ultrashort optical probe pulse with a THz pulse inside an electro-optic crystal, where the THz field rotates the polarisation of the probe pulse and so by measuring the output optical polarisation the electric field is reconstructed. 

Terahertz Surface Generation

One line of research in the group is on the investigation of surface states of semiconductors and the resulting surface electric field. This static field can mix with an ultrashort optical electric field via a third order process in order to induce a second order optical rectification of the impinging pulse. This optical rectification of an ultrashort pulse results in the generation of a new electric field with frequencies in the terahertz region. Furthermore, due to the generation occuring in the surface of the material (on the order of the penetration depth of optical light), surface semiconductor THz emitters provide record efficiencies per unit thickness when compared to other generation mechanisms. We are currently investigating these THz emission properties with the goal of developing even more efficient, ultra-thin planar THz emitters with applications in THz imaging.

Terahertz Imaging

Terahertz imaging is important for the security industry as it opens the possibility for single shot, non invasive imaging of weapons and/or contraband. The main issue surrounding terahertz imaging is the relatively long (mm scale) wavelength and so the image resolution is limited by the diffraction limit of light. One way that terahertz imaging has overcome this diffraction limit in the past is to image the system in the near field region where subwavelength resolutions are possible. Our research in terahertz imaging involves alternative and more practical techniques to overcome such a strict resolution limit. 

Terahertz Antennas

The generation and detection of terahertz radiation using photoconductive switches on antennas is a very common method and is promising due to the small size of such a device. Investigations of how this technology can be improved is another of our terahertz research areas, where we are attempting to design and fabricate a new kind of photoconductive antenna.