Spanning the frequency ranges between the infrared spectrum and gigahertz waves, terahertz waves are currently severely limited by the absence of suitable devices and materials allowing to control them. 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, presented in Nature Communications, paves the way for a practical use of terahertz waves, in particular for imaging and telecommunications.
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 we have therefore come to the hypothesis that it should be possible to use graphene to manage terahertz waves," Kuzmenko explains.
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 us to control the number of electrons in graphene and thus allows more or less light to pass through, with the magnetic field, which bends the electronic orbits, we have been able to control not just the intensity of the terahertz waves, but also their polarisation," comments Jean-Marie Poumirol, a member of the UNIGE research team and the first author of the study. "It is rare that purely electrical effects are used to control magnetic phenomena."
Scientists are now able to apply such control over a complete range of terahertz frequencies.