Grant: Discovery Grants Program - Individual

Light has always been one of our most important tools to study nature and to communicate information. Optical communication is as old as mankind, and microscopes have been used for centuries to explore living organisms. However, it quickly became clear that conventional microscopes cannot resolve structures which are smaller than the wavelength of light - roughly one thousandth of a millimetre. The last three decades have seen remarkable progress in both fields through the invention of the laser, optical fibres, and new designs of optical materials. It is now possible to observe structures that are much smaller than the wavelength of light, and novel materials make optical switching possible: the path of one flash of light can be changed by switching on another light pulse. This phenomenon has been studied, e.g., for the design of an all-optical computer. In our project, we will study optical switching with the weakest possible light pulses, which are called photons. At such low intensities, light behaves very differently from what we are used to. For instance, after two photons have passed through an optical switch, it may happen that the path of the first light pulse depends on whether we try to observe the second pulse or not. Because optical switches work best at high light intensities, this process has not yet been observed in experiments. However, related phenomena are already used by a number of companies to encrypt messages and, during the last ten years, new approaches in the design of optical materials have brought optical switches for photons close to become reality. We will investigate how metal films can be used to build optical switches for photons. It is known that a very thin layer of gold or silver can help to concentrate light on a small area at the metal surface. This phenomenon increases the light intensity at the metal film, which would be useful for optical switching. Because concentrating light on small areas is also useful to increase the resolution of a microscope, we will also employ our ideas to find ways to improve the resolution of special types of microscopes.