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Wednesday, 5 February 2020

New Graphene Device Detects and Amplifies Terahertz Waves

In recent years, physicists and engineers have learned to detect and control almost the entire electromagnetic spectrum, from UVs to infrared to gamma rays. However, a range of frequencies still escaped scientists: the terahertz frequency (THz). But recently, a team of researchers has developed a THz graphene detection device capable of amplifying THz waves. A real scientific feat that could lead to a whole new technological era.

Terahertz (THz) waves lie between microwaves and infrared in the electromagnetic frequency spectrum, but due to their low energy, scientists have not been able to exploit their potential. The riddle is known in scientific circles as the "terahertz divide".

Being able to detect and amplify THz waves (T rays) would open up a new era of medical, communication, satellite, cosmological and other technologies. A major application would be a safe and non-destructive alternative to X-rays. However, so far, the wavelengths involved, which vary between 3 mm and 30 μm, have proven to be impossible to use due to relatively weak signals from from all existing sources.

Place THz waves in the electromagnetic spectrum. Credits: Y. Chassagneux

A THz wave amplifier based on graphene

A team of physicists has created a new type of optical transistor - a functional THz amplifier - using graphene and a high-temperature superconductor. The physics behind the amplifier is based on the properties of graphene, which is transparent and not sensitive to light and whose electrons are “massless”. It is made up of two layers of graphene and a superconductor which trap the “massless” electrons of graphene between them like a sandwich.

THz radiation hits the device and is re-emitted with amplified energy. Credits: Loughborough University

The device is then connected to a power source. When THz radiation hits the outer graphene layer, the trapped particles inside it attach to the outgoing waves, amplifying them. Professor Fedor Kusmartsev of the Loughborough Physics Department explains: “When the THz light hits the sandwich, it is reflected like a mirror. The main point is that there will be more reflected light than that which hit the device."

"It works because external energy is supplied by a battery or by light hitting the surface from other higher frequencies of the electromagnetic spectrum. THz photons are transformed by graphene into massless electrons, which, in turn, are transformed back into reflected and energized THz photons. Because of such a transformation, THz photons get their energy from graphene - or the battery - and weak THz signals are amplified.”

Towards control of the THz frequency and the advent of a new technological era

The study was published in the journal Physical Review Letters . The team continues to develop the device and hopes to have prototypes ready for testing soon. Professor Kusmartsev said he hopes to have an operational amplifier ready to go on the market in about a year. He added that such a device would greatly improve current technology and allow scientists to reveal more about the human brain.

The THz amplifier is small enough to fit into many technologies. Credits: Loughborough University

“The universe is full of terahertz radiation and signals. In fact, all biological organisms absorb and emit them. I hope that with such an amplifier available, we will be able to discover many mysteries of nature. For example, how chemical reactions and biological processes happen, or how our brain works at the thought level,” says Kusmartsev.

"It has properties that would greatly improve vast scientific fields such as imaging, spectroscopy, tomography, medical diagnosis, health monitoring, environmental monitoring and chemical and biological identification. The device we have developed will allow scientists and engineers to exploit this bandwidth and create the next generation of medical equipment, detection equipment and wireless communication technology,” he adds.


Optical transistor for amplification of radiation in a broadband terahertz domain

Phys. Rev. Lett.

K. H. A. Villegas, F. V. Kusmartsev, Y. Luo, and I. G. Savenko

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