Researchers from the University of Sussex have designed a large-area, but extremely thin semiconductor surface source of terahertz, which is made up of only a few atomic layers and can be used with present-day electronic platforms.
Terahertz sources are known to produce short pulses of light that oscillate at 'trillions of times per second.' These sources at this scale are so fast that they cannot be controlled by traditional electronics, and, until now, they were very slow to be controlled by optical technologies.
This fact holds major implications for the emergence of ultra-fast communication devices, whose limit is above the 300 GHz, such as the one needed for 6G mobile phone technology—something that is still essentially beyond the limit of existing electronics.
Scientists in the Emergent Photonics (EPic) Lab at the University of Sussex and headed by Marco Peccianti, Professor and Director of the Emergent Photonics (EPic) Lab, are experts in surface terahertz emission technology and have accomplished the thinnest and brightest surface semiconductor sources revealed to date.
The emission region of the latest development—that is, a semiconductor source of terahertz—is 10 times thinner than the semiconductor source achieved before, and it also delivers similar or even better performance.
The thin atomic layers can be mounted on top of the present-day devices and objects, which means they are capable of placing a terahertz source in regions that would have been unimaginable otherwise, such as day-to-day objects like a teapot or even a work of art—thus paving the way for 'internet of things' and anti-counterfeiting—and even formerly incompatible electronics, like the advanced mobile phones.
From a physics perspective, our results provide a long-sought answer that dates back to the first demonstration of terahertz sources based on two-colour lasers. Semiconductors are widely used in electronic technologies but have remained mostly out of reach for this type of terahertz generation mechanism. Our findings therefore open up a wide range of exciting opportunities for terahertz technologies.
Dr Juan S. Totero Gongora, Leverhulme Early Career Fellow, University of Sussex
Dr Luke Peters, a Research Fellow of the European Research Council project TIMING at the University of Sussex, stated, “The idea of placing terahertz sources in inaccessible places has great scientific appeal but in practice is very challenging. Terahertz radiation can have a superlative role in material science, life science and security. ”
“Nevertheless, it is still alien to most of the existing technology, including devices that talk to everyday objects as part of the rapidly expanding ‘internet of things.’ This result is a milestone in our route to bring terahertz functions closer to our everyday lives,” Dr Peters added.
Terahertz waves, which lie between infrared and microwaves in the electromagnetic spectrum, are a type of radiation that is highly sought in both industry and research.
These waves have a natural potential to expose the material composition of a certain object by effortlessly entering standard materials, such as plastic, clothes and paper in the same manner as X-rays do but without causing any harm.
With terahertz imaging, scientists can 'see' the molecular composition of objects and differentiate between different types of materials.
Earlier developments made by Professor Peccianti’s research team demonstrated the promising applications of terahertz cameras, which could be a game-changer in airport security and medical scanners—like those used for detecting skin cancers.
For researchers working in terahertz technology, one of the major difficulties faced by them is that what is generally accepted as an 'intense terahertz source' is bulky and faint in comparison to a light bulb, for instance. In the majority of the cases, the requirement for highly exotic materials, including nonlinear crystals, renders them costly and unwieldy.
This need presents logistical concerns for incorporation with other technologies, like ultrafast communications and sensors. But these limitations have now been resolved by the team from the University of Sussex by creating terahertz sources from very thin materials (around 25 atomic layers).
The researchers illuminated an electronic-grade semiconductor using two different kinds of laser light, with each light oscillating at a different color or frequency, and successfully elicited the emission of brief pulses of terahertz radiation.
This scientific innovation has historically fascinated researchers working in this domain ever since the terahertz sources based on two-color lasers were initially demonstrated in the early 2000s.
The two-color terahertz sources based on unique mixtures of gas, like krypton, argon, or nitrogen, are one of the best performing sources available at present. Semiconductors, which are extensively utilized in electronic technologies, have remained largely beyond the reach of this kind of terahertz generation mechanism.
The study was designed a part of the framework of the European Research Council project, called “TIMING.”
Gongora. J. S., T., et al. (2020) All-Optical Two-Color Terahertz Emission from Quasi-2D Nonlinear Surfaces. Physical Review Letters. doi.org/10.1103/PhysRevLett.125.263901.