The terahertz range lies between infrared and microwave spectra. Terahertz radiation can penetrate living tissues, but, unlike X-rays, is not ionizing and poses no health hazard. Therefore, medical practitioners could benefit immensely from compact terahertz scanners that can obtain pictures of tissues in a living organism. In addition, terahertz waves are currently employed for the development of high-speed communication systems based for aerospace industry, where the size of equipment plays a critical role.

Researchers from Aston University and ITMO University used quantum dots to develop an antenna that can help significantly reduce the size of terahertz sources. The work was supported by scientists from the University of Strathclyde and University of Sheffield, as well as TeraVil Ltd company and Center for Physical Sciences and Technology in Vilnius.

"It was a technological challenge," says academic supervisor of the study Edik Rafailov, professor at Aston Institute of Photonic Technologies and leading research associate at ITMO University. "We demonstrated that quantum dots are a good alternative for conventional semiconductors. This new technology gives us an opportunity to generate terahertz at room temperature. And potentially make terahertz devices compact and cheap."

Today terahertz generation relies on sources that involve conversion of infrared laser beam into terahertz. The transformation is carried out with intricate systems of waveguides, semiconductor crystals or diodes. The search for alternative ways of generating and detecting terahertz waves is still under way, but such devices remain bulky, expensive and operate only at low temperatures.

The antennas, developed by the scientists, make it possible not only to use terahertz sources at room temperature, but also to miniaturize them. "We are able to create very compact sources of terahertz radiation that can fit on a fingertip," comments leading author of the paper Andrei Gorodetsky, researcher at the Department of Photonics and Optical Information Technology of ITMO University and research associate at Aston Institute of Photonic Technologies. "With the new antennas, we managed to remove the limitation associated with narrow light spectrum that is used by current converts. This gives us an opportunity to combine the antennas with compact infrared lasers. Besides, the antennas are 20 times more resistant to damage than typical semiconductor devices. Both factors allow us to incorporate the antenna into the laser, instead of setting it apart."

The researchers suggest that their findings can be used in high-speed communication systems and also in compact terahertz scanners, which would give dynamic imaging of deep skin layers, embryo development, processes occurring in the brain, other internal organs or tumors. Terahertz radiation is not harmful does not scatter too much in biological objects. As a result, terahertz systems will be more informative, sensitive and fast compared to their substitutes from other parts of electromagnetic spectrum.

Reference:

Ross R. Leyman, Andrei Gorodetsky, Natalia Bazieva, Gediminas Molis, ArunasKrotkus, Edmund Clarke, and Edik U. Rafailov (2016), Quantum dot materials for terahertz generation applications, Laser & Photonics Reviews,

http://onlinelibrary.wiley.com/doi/10.1002/lpor.201 500 176/abstract

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