Nano particles unexpectedly enable light to move more quickly

Research is editorial highlight in Physical Review Letters

13 November 2015

Researchers at AMOLF have discovered a surprising effect during experiments in which circulating light is ‘locked’ in a cavity. They found that the presence of nano particles near the cavity can increase the speed of the circulating light. From the University of Amsterdam (UvA), PhD student Hugo Doelman and professor by special appointment Femius Koenderink from the Institute of Physics took part in the research.

The observed effect runs counter to the expectation going back 70 years that the breaking index of the particles predicts light speed. If that were the case, the nano particles would in fact slow down the light. The radiation of the particles appears to account for this surprising effect. The particles furthermore cause the light to remain locked up in the cavity for longer. This is an important finding because the measurement of these kinds of changes in light speed form the foundation for extremely sensitive sensors.

The research results were published on 11 November in Physical Review Letters. The editorial team chose the research as an editorial highlight. Hugo Doelman, a UvA PhD student, is a second author for the article.

Breaking index

The researchers used a doughnut-shaped glass cavity for the experiment, which light could circulate around for a long time. They placed gold nano particles close to the doughnut. To their surprise, the researchers saw that the effect of the nano particles was to increase the light speed and also to increase how long it remained contained in the cavity. Until now, scientists had thought that the opposite would happen: that the light would slow down because the high breaking index of the nano particles changes the light speed in the doughnut. The surprising results of the experiment can be explained by the radiation given off by the nano particles and the cavity. The escaping light reacts with the radiation from the nano particles, which increases the light speed in the cavity.

Sensors and other systems

The demonstration in this experiment of the influence of radiation on light speed is important for the development of sensors. Many modern sensitive sensors are based on precise measurement of light speed. The results could also lead to other research into all sorts of systems in which radiation or other forms of energy loss play a role. According to research leader Ewold Verhagen, 'It's tempting to neglect the fact that systems lose energy through friction, resistance and radiation. It makes it easier to describe phenomena in physics, such as sound vibrations and electrical flows. The unexpected relevance of energy loss teaches us that it can be useful to reassess other systems too.'


'Perturbing Open Cavities: Anomalous Resonance Frequency Shifts in a Hybrid Cavity-Nanoantenna System', Freek Ruesink, Hugo M. Doeleman, Ruud Hendrikx, A. Femius Koenderink, and Ewold Verhagen, Physical Review Letters

Anomalous Resonance Frequency Shifts in a Hybrid Cavity-Nanoantenna System.png

Light waves (blue arrow) can circulate up to a million times in the cavity before escaping (green arrow). If the light escaping from the glass cavity interferes with the light wave from the nano particle (orange), the light speed in the cavity increases rather than decreases

Bron: FOM

Published by  Faculty of Science