Nonlinear and quantum optics in the presence of plasmonic effects

光一直是我们研究自然和交流信息的最重要的工具之一。光通信和人类一样古老，显微镜被用来探索活的有机体已经有几个世纪了。然而，人们很快发现，传统的显微镜无法分辨小于光波长的结构--大约是千分之一毫米。在过去的三十年里，通过激光、光纤和光学材料的新设计的发明，这两个领域都取得了显著的进步。现在可以观察到比光的波长小得多的结构，新材料使光学开关成为可能：一束光的路径可以通过打开另一束光脉冲来改变。这种现象已经被研究过，例如用于全光计算机的设计。 在我们的项目中，我们将研究具有最弱光脉冲的光开关，这种光脉冲被称为光子。在如此低的强度下，光的行为与我们习惯的非常不同。例如，在两个光子通过光开关后，第一个光脉冲的路径可能取决于我们是否尝试观察第二个脉冲。由于光学开关在高光强下工作得最好，这一过程还没有在实验中观察到。然而，相关现象已经被一些公司用来加密信息，在过去的十年里，光学材料设计的新方法使光子的光学开关接近成为现实。我们将研究如何使用金属薄膜来建立光子的光学开关。众所周知，一层非常薄的金或银可以帮助将光线集中在金属表面的一小块区域上。这种现象增加了金属膜上的光强度，这对光开关是有用的。由于将光线集中在小区域也有助于提高显微镜的分辨率，我们还将利用我们的想法来寻找提高特殊类型显微镜的分辨率的方法。

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.