Terahertz source seeks road to market

22 Nov 2002

UK scientists unveil a convenient scheme for producing tunable terahertz radiation.

Researchers at the University of Leeds, UK claim to have developed a new simple way to generate continuously tunable terahertz radiation. They have patented the technique and are now looking for partners interested in commercializing the work.

The system uses a Ti:Sapphire laser, a glass Fabry-Perot etalon and a photoconductive antenna to generate terahertz waves by difference-frequency generation (DFG). This technique takes two light beams of very similar frequencies, say A and B, and mixes them together to generate a new signal with a frequency of A-B.

Although DFG has previously been used to create terahertz radiation, the novel aspect of the Leeds approach is that it creates the two beams for mixing from a single laser cavity rather than two discrete lasers. Potentially, this could result in tunable terahertz sources that are smaller and cheaper than current systems.

By placing a Fabry-Perot etalon into the cavity of a Ti:Sapphire laser the researchers can produce stable oscillation of two widely-separated laser modes. These modes are then mixed in the photoconductive antenna to create terahertz radiation. By varying the thickness of the etalon, the mode separation and thus the frequency of the terahertz output beam are tuned. To date, output at 0.3 and 0.5 THz has been demonstrated.

"The system is easy to set up and is robust," explained Bob Miles, a member of the Leeds research team. "There is no need for frequency synchronization or beam alignment." Miles says that tuning from the microwave region to several terahertz is possible. The output power is limited by conversion efficiency and the maximum is currently around 1 microW in continuous wave mode.