Posted in | NanoOptics

Recent Research Challenges Widely-Held Understanding of Electromagnetic Radiation

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A recent study from the University of Strathclyde challenged a well-established understanding of electromagnetic radiation.

The study discovered the possibility of breaking the standard direct correspondence between the bandwidths of the current source and emitted radiation. This was accomplished by extracting narrowband radiation with superior efficiency, without making the oscillation of the current narrowband.

The findings resulted in the production of narrowband light sources in media where electromagnetic radiation would normally not be possible. It is considered to be a powerful tool for scientists, enabling them to understand the behavior of materials, or even biological molecules under varied conditions, which has a tremendous impact on the lives of people by developing new medical treatments and products.

The research, featured in Scientific Reports, also involved researchers at the Ulsan National Institute of Science and Technology (UNIST) and the Gwangju Institute of Science and Technology (GIST), both in South Korea.

Professor Dino Jaroszynski, of Strathclyde’s Department of Physics, headed the study.

Coherent light sources such as lasers have many uses, from communication to probing the structure of matter. The simplest source of coherent electromagnetic radiation is an oscillating electric current in an antenna. However, there are many other devices are based on these basic laws of physics, such as the free-electron laser, which produces coherent X-ray radiation, or magnetrons found in microwave ovens. Our study has shown that some common media with interesting optical properties can be taken advantage of if we imbed, or bury, an oscillating current source in them.  Media such as plasma, semiconductors and photonic structures have a ‘cut-off’, where propagation of electromagnetic radiation with frequencies lower than the ‘cut-off’ frequency is not possible;  we noticed that the radiation impedance is increased at the cut-off.

Dino Jaroszynski, Strathclyde

“One consequence of this is that, for a broadband current source immersed in this type of dispersive medium, the cut-off frequency ‘mode’ is selectively enhanced due to Ohm’s law, resulting in narrow bandwidth emission. What is curious is that novel physics should still be hidden in the classical cut-off behavior; in our research, we uncovered a hidden face of the cut-off and realised a new paradigm of narrowband light sources in media that would not usually allow electromagnetic radiation to propagate. This is a remarkably simple idea based on straightforward physics theory that seems to have been overlooked.

“This is a very exciting theoretical discovery that comes out of a very fruitful cross-continental collaboration. It shows that we should always keep an open mind and question even very basic assumptions. We hope to demonstrate this phenomenon at the Strathclyde-based Scottish Centre for the Application of Plasma-based Accelerators; there are numerous applications of electromagnetic radiation and the proposed source should have a large impact if we are able to demonstrate it experimentally.”

This new discovery is scientifically interesting, because it leads us to see the phenomenon of electromagnetic radiation from a completely different viewpoint. We hope the fruitful international collaboration, which brought us to this theoretical discovery, will continue with the experimental demonstration of the idea.

Professor Min Sup Hur, UNIST

Contemporary light sources, or, more generally, electromagnetic sources employed as scientific tools need excellent coherency, monochromaticity, and increased emission power. Coherency and narrow bandwidth or monochromaticity are vital properties of electromagnetic radiation that enable it to be used to observe variations in the structure of materials subject to stimuli, such as a short powerful laser pulse; material properties are deduced from modifications that are made apparent in pump-probe studies.

An analogy would be developing a movie by assembling several time lapse snapshots in order to animate the changes that occur in the material after it has been stimulated.

The key challenge is making high power sources of electromagnetic radiation monochromatic. This is frequently done by making the oscillating current narrowband or filtering the spectrum, which is extremely inefficient. It is complicated, and can also be costly, to decrease the bandwidth of a current source while increasing or maintaining its radiated power.

The Research Excellence Framework 2014, the comprehensive rating of UK universities’ research, ranked the University of Strathclyde’s Physics research first in the UK, with 96% of output evaluated as globally leading or internationally outstanding.

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