Researchers at the University of Leeds’ Institute of Microwaves and Photonics have developed a novel way of generating continuous tuneable Terahertz (THz) radiation.
Terahertz radiation, or far-infrared radiation, is light with a frequency in the range of 0.1 to 30 THz. It is the final ‘gap’ in the electromagnetic spectrum between microwaves and the infrared devices. And by developing devices that can emit and detect such radiation, designers can build products for all sorts of applications including greenhouse gas and ozone mapping, miniaturised radar, and imaging.
The new patented method is simple, robust and eliminates the need for alignment and frequency-stabilisation. It can also be used with any continuous-wave (CW) laser having a broad lasing line that is inhomogeneously broadened.
A Fabry-Perot etalon is inserted into the laser cavity and forces the laser to oscillate on two modes separated by a frequency in the THz range. The two modes are then photomixed to obtain difference frequency radiation, producing THz emission.
An inhomogeneously broadened laser oscillates on a number of modes, which can be very large and is determined by the laser linewidth and the properties of the laser cavity. Inserting a Fabry-Perot etalon into the cavity acts a filter, suppressing all modes except those fulfilling the etalon resonance condition, given by the optical path of the etalon. The mode separation is therefore determined entirely by the etalon, enabling the emitted THz frequency to be tuned by varying the etalon thickness.
The researchers have experimentally demonstrated the effectiveness of this method of THz generation by using a Ti-sapphire laser with glass Fabry-Perot etalons and a photoconductive antenna photomixer to produce radiation of 0.5 THz and 0.3 THz.
Leeds University is participating in Teravision – a 3-year research project funded by the European Commission to develop compact Terahertz frequency systems for imaging and other applications.