Terahertz waves (THz) sit between microwaves and infrared in the light frequency spectrum, but due to their low-energy scientists have been unable to harness their potential. The conundrum is known in scientific circles as the terahertz gap. Being able to detect and amplify THz waves (T-rays) would open up a new era of medical, communications, satellite, cosmological, and other technologies. One of the biggest applications would be as a safe, non-destructive alternative to X-rays. However, until now, the wavelengths – which range between 3mm and 30μm – have proved impossible to utilize due to relatively weak signals from all existing sources. A team of physicists has created a new type of optical transistor – a working THz amplifier – using graphene and a high-temperature superconductor. The physics behind the simple amplifier relies on the properties of graphene, which is transparent and is not sensitive to light and whose electrons have no mass. It is made up of two layers of graphene and a superconductor, which trap the graphene massless electrons between them, like a sandwich. The device is then connected to a power source. When the THz radiation hits the graphene outer layer, the trapped particles inside attach themselves to the outgoing waves giving them more power and energy than they arrived with – amplifying them. Professor Fedor Kusmartsev, of Loughborough’s Department of Physics, said: “The device has a very simple structure, consisting of two layers of graphene and superconductor, forming a sandwich (as shown above). “As the THz light falls on the sandwich it is reflected, like a mirror. The main point is that there will be more light reflected than fell on the device. “It works because external energy is supplied by a battery or by light that hits the surface from other higher frequencies in the electromagnetic spectrum. The THz photons are transformed by the graphene into massless electrons, which, in turn, are transformed back into reflected, energized, THz photons. “Due to such a transformation the THz photons take energy from the graphene – or from the battery – and the weak THz signals are amplified.” The breakthrough – made by researchers from Loughborough University, in the UK; the Center for Theoretical Physics of Complex Systems, in Korea; the Micro/Nano Fabrication Laboratory Microsystem and THz Research Center, in China and the AV Rzhanov Institute of Semiconductor Physics, in Russia – has been published in Physical Review Letters, in the journal, American Physical Society (APS). The team is continuing to develop the device and hopes to have prototypes ready for testing soon. Prof Kusmartsev said they hope to have a working amplifier ready for commercialization in about a year. He added that such a device would vastly improve current technology and allow scientists to reveal more about the human brain. “The Universe is full of terahertz radiation and signals, in fact, all biological organisms both absorb and emit it. “I expect, that with such an amplifier available we will be able to discover many mysteries of nature, for example, how chemical reactions and biological processes are going on or how our brain operates and how we think. “The terahertz range is the last frequency of radiation to be adopted by humankind. Microwaves, infrared, visible, X-rays and other bandwidths are vital for countless scientific and technological advancements. “It has properties which would greatly improve vast areas of science such as imaging, spectroscopy, tomography, medical diagnosis, health monitoring, environmental control and chemical and biological identification. “The device we have developed will allow scientists and engineers to harness the illusive bandwidth and create the next generation of medical equipment, detection hardware and wireless communication technology.” Reference: “Optical Transistor for Amplification of Radiation in a Broadband Terahertz Domain” by K. H. A. Villegas, F. V. Kusmartsev, Y. Luo and I. G. Savenko, 26 February 2020, Physical Review Letters.DOI: 10.1103/PhysRevLett.124.087701
