A team of researchers at the University of Geneva (UNIGE), working with the Federal Polytechnic School in Zurich (ETHZ) and two Spanish research teams, have developed a technique based on the use of graphene, which allows for the potentially very quick control of both the intensity and the polarization of terahertz light. This discovery paves the way for a practical use of terahertz waves, in particular for imaging and telecommunications.
The terahertz waves span frequency ranges between the infrared spectrum (used, for example, for night vision) and gigahertz waves (which find their application, among other, in Wi-Fi connections). Terahertz waves allow for the detection of materials that are undetectable at other frequencies. However, the use of these waves is severely limited by the absence of suitable devices and materials to control them.
Graphene is a single atomic layer of carbon atoms that form a honeycomb network. It is found for example in graphite, the main constituent of pencil rods. In the Department of Quantum Matter Physics of UNIGE’s Faculty of Sciences, Alexey Kuzmenko’s team has been working on graphene’s physical properties for several years. The interaction between terahertz radiation and the electrons in graphene is very strong and they have therefore come to the hypothesis that it should be possible to use graphene to manage terahertz waves.
Working within the framework of the European project Graphene Flagship, scientists have made a graphene-based transistor adapted to terahertz waves. By combining the electrical field, which enables scientist's to control the number of electrons in graphene, thus allowing more or less light to pass through, with the magnetic field, which bends the electronic orbits. They have been able to control not just the intensity of the terahertz waves, but also their polarization. Scientists are now able to apply such control over a complete range of terahertz frequencies.
Now the team’s focus is to move on from the prototype, and develop practical applications and new opportunities by controlling terahertz waves. Their objective is to make terahertz waves industrially competitive in the next few years. There are two main areas of application for this innovation, the first being communications. Using a film of graphene associated with terahertz waves, they should be potentially able to send fully-secured information at speeds of about 10 to 100 times that of Wi-Fi.
The second sphere of application is that of imaging. Being non-ionising, terahertz waves do not alter DNA and therefore are very useful in medicine, biology and pharmacy. Additionally, the control of the circular polarization of the terahertz waves will allow distinction between different symmetries (left-handed or right-handed) of biological molecules, which is a very important property in medical applications. Furthermore, there is potentially a very powerful application of these waves in homeland security. Terahertz waves are stopped by metals and are sensitive to plastics and organic matter. This could lead to more effective means of detecting firearms, drugs and explosives carried by individuals, and could perhaps serve as a tool to strengthen airport safety.
