A new generation of technology is now possible thanks to a revolutionary device made from graphene. In a newly published paper, researchers claim they have built an amplifier that unlocks the frequencies between infrared light and microwaves, a previously unused bandwidth known as the terahertz gap.

The researchers are certain this will have applications in medicine, as it allows for non-invasive and non-destructive probing. They also claim it can be used in “ultra-high bandwidth wireless communication networks, vehicle control, atmospheric pollution monitoring, inter-satellite communication, and spectroscopy.”

The EM Spectrum and the Terahertz Gap

Classically speaking, electromagnetic (EM) radiation is the oscillations in both the electrical and magnetic fields, which propagate perpendicular to each other. That is, a perturbation in one, such as the movement of an electron or a magnet, causes an equal yet 90 degree offset perturbation in the other. The EM spectrum is the broad range of all frequencies and wavelengths of EM radiation, including radio waves, microwaves, infrared, visible light, ultraviolet light, x-rays, and gamma rays. Therefore, your radio, your microwave oven, your eyes, the x-ray machine at the doctor’s office, etc. all make use of essentially the same phenomenon.

As can be seen here, the visible spectrum is only a small sliver of the EM spectrum. On the left are higher frequency gamma rays, while on the left are longer frequency radio waves. (distributed under a CC BY-SA 3.0 license)

However, physicists have been unable to utilize a small band between the infrared and microwave region of the EM spectrum, around 10^12 Hertz, which is a measurement of oscillations per second. Generating and receiving higher and lower frequencies is well understood and already highly utilized, but this particular frequency range causes problems for current methods due to limitations at the nano-scale. Therefore, this has become a well known and frustrating limitation commonly known as the terahertz gap.

In particular, the terahertz gap has vexed physicists because of the many unique yet out of reach uses it has to offer. For example, it is non-ionizing, meaning it does not carry enough energy to remove electrons from an atom. Therefore, it is a safer alternative for x-rays or other forms of medical imaging.

Also, terahertz frequencies are great for security scanning, as they can get through opaque materials and can offer much higher resolution imaging. This is because they are not as susceptible to Rayleigh scattering, which is the scattering of radiation off of air molecules.

Furthermore, a lot of interesting physics happens in this range. For example, Chemistry World says that “molecular excitations, such as rotations and vibrations, lie in the THz range.” Without access to this range, scientists of all kinds are missing out on a trove of useful information.

Quite astoundingly, this range of frequencies can also be used to transmit data 20 times faster than WiFi.

Even though some progress has been made in the last few years, the terahertz gap has been difficult to fill.

Graphene Amplifiers

Fortunately, physicists have found a way to easily access this mysterious range of frequencies. By using a mixture of graphene and a superconductor, they created a material that can absorb terahertz frequencies and emit a much stronger signal, making them useful for a broad range of uses.

More specifically, a high temperature superconductor is sandwiched between 2 layers of graphene, which is a one atom thick material composed entirely of carbon atoms. Being so thin, graphene is virtually transparent to all kinds of radiation, including terahertz frequencies. Graphene has a myriad of other amazing qualities, including having free electrons due to how carbon atoms bond with other carbon atoms in this hexagonal shape.

Superconductivity is a phenomenon where a material loses all electrical resistance. For this to happen, specific materials need to be brought down to a very low temperature (usually below -200 C). High temperature superconductors can achieve this at temperatures above -200 C, making them more useful in practical applications.

When sandwiched between two layers of graphene, the high temperature superconductor traps graphene’s free electrons. This device is then hooked up to a power source, thus making these electrons more energetic. When terahertz radiation is shone on the device, these energetic electrons absorb it, transfer their extra energy, and reflect a more energetic form of the radiation, as explained by the photoelectric effect. Therefore, the researchers have found a clever way to amplify the weak terahertz frequencies into something usable. They claim they have shown that “graphene deposited on superconductor may strongly amplify electromagnetic radiation that opens a door for numerous applications of THz radiation.”

Now that the terahertz gap has been filled, new types of devices are possible, some of which will revolutionize communication, medicine, security, among many other fields.

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