Mirror, mirror

Tuesday 7 May 2013

Scientists at the University of St Andrews have demonstrated that chaos is sometimes a good thing in science.

The work, which demonstrates a six-fold increase in light storage, could lead to faster, cheaper and more efficient LEDs and solar cells.

The research involved a study of optical cavities – also known as optical resonators – and their ability to store light. Optical cavities typically store light by bouncing it many times between sets of suitable mirrors.

In an international collaboration with researchers in Saudi Arabia, the researchers deformed mirrors to disrupt the regular light path in an optical cavity. The team were surprised to find that the resulting chaotic light paths allowed for more light to be stored than with ordered paths.

The experimental work was carried out at the University of St Andrews by Dr Andrea Di Falco and Professor Thomas Krauss.

Dr Di Falco, who leads the Synthetic Optics group at the University’s School of Physics & Astronomy, said, “The concept behind broadband chaotic resonators for light harvesting applications is very profound and complex. I find it fascinating that whilst we used state-of-the-art fabrication techniques to prove it, this idea can in fact be easily applied to the simplest of systems. For example, our collaborators managed to increase the absorption of light in plastic spheres, by simply compressing them.”

“Standard resonators can typically trap light efficiently if it is of one specific colour (wavelength), because each colour behaves in a different way inside the resonator.  As a result it is difficult to inject light of many colours inside them. We have shown that resonators with deformed mirrors cause the different colours behave in the same way, hence making multi-coloured light storage more efficient.”

Professor Krauss, now at the University of York, added, “Our results also have real-world practical implications. The cost of many semiconductor devices, such as LEDs and solar cells, is determined to a significant extent by the cost of the material. Our findings enable more than six times the energy without increasing the amount of material and without increasing the material costs.”

The work has important applications for many branches of physics and technology, such as quantum optics and processing optical signals over the internet, where light needs to be stored for short periods of time to facilitate logical operations and to enhance light-matter interactions.

Solar cells may also benefit, as trapping more light in solar cells improves their ability to generate electricity. The longer light is contained in the solar cell, the greater the chance that it will be absorbed and create electricity.

The project was led by Professor Andrea Fratalocchi of the King Abdullah University of Science and Technology (KAUST). He said, “Chaos, disorder and unpredictability are ubiquitous phenomena that pervade our existence and are the result of the never-ending evolution of nature.

“The majority of our systems try to avoid these effects, as we commonly assume that chaos diminishes the performance of existing devices. The focus of my research, conversely, is to show that disorder can be used as a building block for a novel, low-cost and scalable technology that outperforms current systems by orders of magnitude.”

The project, which also involved researchers from Bologna University, Italy, was funded by KAUST University and the UK Engineering and Physical Sciences Research Council (EPSRC), through Dr Di Falco’s fellowship and the UK Silicon Photonics project.

The study is reported in the current issue of Nature Photonics.


Note to Editors

The paper is available online.

The researchers are available for interview:

Dr Andrea Di Falco: [email protected]; tel: +44 (0)1334 463165; website: www.st-andrews.ac.uk/physics/synthopt/

Professor Thomas Krauss: Via the University of York Press Office: [email protected] or +44 (0) 1904 322029

Note to Picture Editors

Images are available from the Press Office – contact details below.

Issued by the Press Office.
Contact Senior Communications Manager Gayle Cook on 01334 467227 or email [email protected]
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