Terahertz radiation has some interesting properties for imaging applications

Turning DC into terahertz radiation paves way for safer imaging

A device that can turn direct current into terahertz radiation, developed by American researchers, could pave the way for safer medical imaging technology.

Terahertz radiation, the part of the electromagnetic spectrum between microwaves and infra-red, is non-ionising and therefore safe for the human body. As it is highly efficient in differentiating tissues with different water content, it could work well, for example, in identifying tumours. However, engineers have so far struggled to create a controllable source.

The new device, developed by a team from the Universities of New Mexico and New York, takes advantage of instabilities in the oscillation of conducting electrons at the device's surface, a phenomenon known as surface plasmon resonance.

"[Our work] demonstrates a new approach for efficient energy conversation from a DC electric field to coherent, high-power and electrically tunable terahertz emission by using hybrid semiconductors," said Andrii Iurov, who led the scientific team.

The team created a hybrid semiconductor: a layer of thick conducting material paired with two thin, two-dimensional crystalline layers made from graphene, silicene (a graphene-like material made from silicon instead of carbon), or a two-dimensional electron gas. When a direct current passes through the hybrid semiconductor, plasmon instability occurs. This instability induces the emission of terahertz radiation.

"Additionally, our proposed approach based on hybrid semiconductors can be generalised to include other novel two-dimensional materials, such as hexagonal boron nitride, molybdenum disulfide and tungsten diselenide."

By adjusting various parameters, such as the density of conduction electrons in the material or the strength of the DC electric field, it is possible to tune the wavenumber and consequently the frequency of the resulting terahertz radiation.

Previously, other labs have created artificial sources of terahertz radiation, but this design could enable better imaging capabilities than other sources can provide.

"Our proposed devices can retain the terahertz frequency like other terahertz sources but with a much shorter wavelength for an improved spatial resolution in imaging application," said Iurov.

In addition to medical applications, the technology could also be used for wireless data transmission or to detect explosives or hidden weapons.

The study was published in the latest issue of the Journal of Applied Physics.

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