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A graphene-based frequency amplifier will make it possible to harness the elusive terahertz wavelengths for communications, enabling revolutionary technologies.

New Era for Medical, Cosmological and other Technologies

Terahertz (THz) waves lie between microwaves and infrared in the frequency spectrum of light, but their low energy has prevented scientists from realizing their potential.

The conundrum is known in scientific circles as the terahertz gap.

The ability to detect and amplify THz waves (T-rays) would open a new era for medical, communications, satellite, cosmological and other technologies.

One of the most important applications would be as a safe and nondestructive alternative to X-rays. Until now, however, wavelengths from 3 millimeters to 30 picometers could not be used because of the relatively weak signals from all existing sources.

Using graphene and a high-temperature semiconductor, a team of physicists has created a novel optical transistor that functions as a THz amplifier.

The physics behind the amplifier relies on the properties of graphene, which is transparent and insensitive to light and whose electrons have no mass. It consists of two layers of graphene and a superconductor that traps the graphene’s massless electrons between them like a sandwich.

The device, described in Physical Review Letters, is connected to a power supply. When THz radiation hits the outer layer of graphene, particles trapped inside join the outgoing waves, giving them more power and energy than they arrived with, amplifying them.

Professor Fedor Kusmartsev of Loughborough University’s Department of Physics said in a statement, “The device has a very simple structure, consisting of two layers of graphene and superconductor that form a sandwich. When THz light falls on the sandwich, it reflects like a mirror.

“The main point is that more light is reflected than falls on the device. It works because the external energy is supplied by a battery or by incident light from other frequencies higher in the electromagnetic spectrum,” he said.

“The THz photons are converted by the graphene into massless electrons, which in turn are converted back into reflected and energized THz photons. Through such conversion, the THz photons absorb energy from the graphene or battery and the weak THz signals are amplified.”