T-rays could lead to real-life tricorder

Ashley N. Paddock, ashley.paddock@photonics.com

The technology used for full-body security scanners could one day lead to the development of a handheld scanner similar to the tricorder made famous by Star Trek. The device will be suitable for medical scanning thanks to a new technique for creating terahertz waves (T-rays).

Scientists from the Institute of Materials Research and Engineering (IMRE), a branch of the Agency for Science, Technology and Research in Singapore, and from Imperial College London have made T-rays into a much stronger directional beam than previously thought possible and have done so in room-temperature conditions. This breakthrough should allow future T-ray systems to be smaller, more portable, easier to operate and cheaper to develop than current devices.

The researchers say the stronger, more efficient continuous-wave T-rays could be used to make better medical scanning gadgets.

The scanner and detector could function much like the tricorder — a portable sensing, computing and data communications device — because the waves can detect biological events such as increased blood flow around tumorous growths, the researchers say. Future scanners also could perform fast wireless data communication to transfer a high volume of information on the measurements it makes.

T-rays, waves in the far-infrared part of the electromagnetic spectrum, are already in use in airport security scanners, prototype medical scanning devices and in spectroscopy systems for materials analysis. They can sense molecules such as those present in cancerous tumors and living DNA because every molecule has its unique signature in the terahertz range. They also can be used to detect explosives or drugs, to monitor gas pollution, or to nondestructively test semiconductor integrated circuit chips.

Current T-ray imaging devices are very expensive and operate only at a low output power because creating the waves consumes large amounts of energy and must take place at very low temperatures.

In the new technique, the researchers demonstrated that it is possible to produce a strong beam of T-rays by shining light of differing wavelengths on a pair of electrodes — two pointed strips of metal separated by a 100-nm gap on top of a semiconductor wafer. The structure of the tip-to-tip nanosize-gap electrode greatly enhances the terahertz field and acts as a nanoantenna to amplify the wave generated. In this method, terahertz waves are produced by an interaction between the electromagnetic waves of the light pulses and a powerful current passing between the semiconductor electrodes. The scientists can tune the wavelength of the T-rays to create a usable beam in the scanning technology.

"The secret behind the innovation lies in the new nanoantenna that we had developed and integrated into the semiconductor chip," said Dr. Jing Hua Ten of IMRE, who was the lead author of the study. The work was published in Nature Photonics (doi: 10.1038/nphoton.2011.322).

Research author professor Stefan Maier in the laboratory. Courtesy of Imperial College London.

Arrays of these nanoantennas create much stronger terahertz fields that generate a power output 100 times higher than that of commonly used terahertz sources that have conventional interdigitated antenna structures. A stronger T-ray source gives more power and higher resolution to the T-ray imaging devices.

"T-rays promise to revolutionize medical scanning to make it faster and more convenient, potentially relieving patients from the inconvenience of complicated diagnostic procedures and the stress of waiting for accurate results," said Stefan Maier, a visiting scientist at IMRE and professor in the department of physics at Imperial College London.

"With the introduction of a gap of only 0.1 micrometers into the electrodes, we have been able to make amplified waves at the key wavelength of 1000 micrometers that can be used in such real-world applications."