Bringing terahertz waves to heel?

Terahertz waves are frequency ranges of light that lie between infrared radiation (used, for example, in night vision) and gigahertz waves (used for Wi-Fi connections). Although the waves can be used to detect matter that is inaccessible with other frequencies, a lack of suitable devices and materials for controlling them severely restricts their usage. Researchers at the University of Geneva (UNIGE), working in collaboration with Zurich’s École Polytechnique Fédérale (ETHZ) and two Spanish research teams, have developed a graphene-based technique for controlling the intensity and polarisation of terahertz rays at a potentially very fast speed. This discovery, presented in the journal Nature Communications, opens up opportunities for practical applications of terahertz waves in the fields of imaging and communications.

Graphene is a monoatomic layer of carbon atoms that forms a honeycomb lattice. It is found especially in graphite, the material that pencil tips are made of. The team led by Alexey Kuzmenko from the Department of Quantum Physics at UNIGE’s Faculty of Science has been working on the physical properties of graphene for several years. "Since the interaction between terahertz radiation and graphene electrons is very strong, we hypothesised that it should be possible to use graphene to control terahertz waves," explains Kuzmenko.

The scientists created a graphene-based transistor suitable for terahertz waves as part of the European Graphene Flagship project. "We combined the electric field — meaning we could control the number of graphene electrons and the amount of light passing through — with the magnetic field that bends the electron orbits. We were then able to control not just the intensity of the terahertz waves we wanted to let pass but also their polarisation”, continues Jean-Marie Poumirol, UNIGE researcher and the study’s first author, adding: “It’s not very often that purely electrical effects are used to control magnetic phenomena". The scientists are now in a position to apply this type of control over the entire terahertz frequency range.

Practical applications of terahertz waves

The UNIGE researchers are now focusing on the practical applications of their prototype and the possibilities it offers for controlling terahertz waves. The scientists plan to make the waves industrially competitive in the next few years — an innovation that will embrace two main fields, the first of which is communications. "By using our graphene plate in combination with terahertz waves, we should be able to send information that communicates 10 to 100 times more quickly than Wi-Fi or radio waves. At the same time, the transmission should be secure, provided it is over a short distance", continues Jean-Marie Poumirol, in what would be a significant step forward for telecommunications. The second area of application is imaging: since terahertz waves are not ionising, they do not alter DNA — meaning they are a great asset for medicine, biology and medicine. The ultra-fast control of the circular polarisation of terahertz waves will make it possible to distinguish biological molecules with different symmetries (left and right), a very important property for medical applications. Furthermore, the waves are potentially very useful in the area of homeland security: "Metal blocks terahertz waves, which are also sensitive to plastic and organic matter, so it’s possible to detect someone carrying weapons, drugs or explosives with much greater efficiency, which would be ideal in airport checks," concludes Alexey Kuzmenko.

Contact

Alexey Kuzmenko +41 (0)22 379 31 05 - Alexey.Kuzmenko(at)unige.ch
Jean-Marie Poumirol +41 (0)22 379 34 19 - Jean-Marie.Poumirol(at)unige.ch