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Light in moving media

Final Report Summary - MOLIGHT (Light in moving media.)

The main focus of the project MOLIGHT was to study novel effects of propagating light, and in particular how light can be used to create materials that move or change at the speed of light and then study how light itself interacts with such materials.

Light moves at speeds that render its effects in everyday life to be instantaneous. It is very hard to imagine what light looks like when it propagates inside a room or what physical effects will incur when the objects start moving at the speed of light and how interactions between light and the objects will change. Creating objects that move at or close to the speed of light can be extremely hard. The approach followed in MOLIGHT was to use light itself: if light has sufficient intensity then it will modify the properties fro example of piece of glass by creating a change in the material that will propagate together with the light beam, i.e. at the speed of light. We can then study how light or photons interact with this "moving change". Interesting effects that we have studied are the creation of effective event horizons for light, i.e. regions that behave like the horizon of a black hole. By creating so-called analogue or artificial black holes in the lab, we can then study how quantum fields behave in these strongly distorted spacetimes, studying exotic effects such as Hawking radiation or Penrose amplification from a rotating black hole.

By using light to modify material properties, we also studied how light can modify the propagation of light itself or, said differently, we studied how photons can interact with other photons. Typically, photons do not interact with each other but we have studied a regime in which they do and, more importantly, they do so in such a way that makes light behave as if it where a superfluid. We then used our photon superfluid to study the generation and evolution of quantised vortices and the build artificial "Superfluid" stars, also known as Boson stars.

A very important aspect of this project was the development of key technologies that enable the study of light in movement. We therefore developed a new camera system that is based on the detection and timing of single photons. This camera has the time resolution required to freeze light in motion. This was used to make videos of light pulses propagating in thin air or through an optical fibre. Both of these demonstrations were central to the project in terms of providing a means to actually observe the dynamics of light. For example, we were also able to perform studies showing how a superluminal source leads to time-inversion, i.e. the light is seen to propagate backwards. This effect had never been observed before yet, it had been predicted more than 100 years ago by Lord Rayleigh who noted that music played by a supersonically moving source would be perceived to be played backwards. Using light, we were therefore able to provide the first experimental demonstration of the 140 year old prediction.

This camera technology is now being developed to image objects behind corners, see through fog and inside the human body. This is a clear demonstration of how the study of fundamental physics questions can lead to the development of technologies that are of global importance.