Nanostructures enhance terahertz light generation

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Researchers from the University of Southampton and Imperial College London have found that quantum wells – 2D nanostructures formed of several layers of semiconductor alloys sandwiched on top of each other – can enhance light emission at terahertz frequencies.

It is hoped that the findings will have an impact on photonic and optoelectronic devices across a broad range of applications, including medical imaging and security scanning.

Electrons are trapped in the structure and this confinement can be exploited to enhance their capacity to interact with light at given frequencies much lower than the laser frequency at which they are excited.

Nathan Shammah, from the University of Southampton’s Quantum Light and Matter (QLM) group and co-author of the study, said: ‘As the 2D nanostructures can be manufactured with an asymmetric design, this allows light to interact with trapped electrons in a way that is not otherwise allowed. This interaction process, leading to the emission of light at lower frequencies, has not been observed in atoms because those are very symmetrical systems and symmetry rules prevent the transitions that trigger this light emission from happening.’

In the paper, which is published in Physical Review B, the researchers predict that by shining light on a 2D asymmetric nanostructure with a laser that is tuned at resonance with the electronic transitions that can occur in the nanostructure, in addition to the scattered laser light, this 2D device would emit light at other frequencies, which can be tuned simply by changing the laser power.

The high efficiency shown by the simulations suggests that this theoretical result could be exploited in the near future for a broad range of optoelectronic applications, from harmless medical imaging and security scanners, to short-range, ultra-fast wireless communication.