Visit of Prof. Oliver Wright

这项研究涉及对等离子激元的研究，等离子体是捕获在金属表面的光的量子。它们可以沿着金属表面移动，我们会寻找方法来调节它们并使它们相互作用。目前，这些等离子激元对彼此的存在非常不敏感，但通过适当地设计金属三明治，我们可以制造出应该优化它们相互作用的结构。我们在这个短暂的休假期间的目的是尝试一个新的想法，我们借用了另一个领域，在这个领域我们已经成功地展示了有史以来最大的光学非线性，在等离子体上进行试验。今天的商业激光系统提供短到10ps的可重复脉冲，使无数应用在科学、医学、制造和通信中成为可能。世界上有大量的共振，每种材料都有特定的波长来增强光与物质的相互作用。因此，也许激光最重要的一个方面是辐射的波长，而控制这一点的方法是重中之重。传统上，激光辐射的光学波长转换或放大是借助于特定晶体、波导或周期性图案化介质中的非线性光学效应来实现的，从而通过二阶或三阶光学非线性效应获得谐波产生或光学参数振荡。当使用非线性大块晶体用于这种目的时，必须使用满足光学相位匹配条件的材料来产生光学非线性。必须严格调整入射光的方向和偏振以及晶体的轴线，温度也必须严格调整。当在这种应用中使用光波导或周期性图案化介质来提高效率时，输出光的调谐范围受到所需的严格几何规格的限制。基于非线性效应的传统光子器件的尺寸和光功率消耗的大幅减小可能使用电磁场的强限制。这种限制的一种建议是使用光子晶体结构。然而，这些结构价格昂贵，并且在多个维度上受到严格的几何约束，我们建议通过利用两个SPP之间的相互作用以廉价、紧凑和简单的结构实现高效的光波长转换。这种方法有可能在光调制、光放大或光频率变换的广泛应用中有效。它的多功能性和光学频率可调谐性使其能够应用于科学、工业和环境应用的各种情况。这种方法与脉冲或连续激光相结合，作为一种光学参数放大器，应该被证明是非常有用的，以扩大可获得的光学频率范围。这同时提供了一种从脉冲激光(例如超连续谱)产生宽带光学频率谱的手段，在医学和超快光谱学中具有特别重要的应用。此外，本发明提供了一种调制从低频到太赫兹范围以上的超高频的光辐射的装置。这在未来电信系统的超高速交换应用中应该是一个福音。本发明还应该在分析设备中找到应用，例如在激光光谱仪、激光测距系统、遥感系统、成像系统和激光功率输送系统中。

The research concerns the study of plasmons, quanta of light which are trapped at the surface of a metal. These can travel along the metal surface, and we seek ways to modulate and make them interact with each other. Currently, these plasmons are very insensitive to each others presence, but by appropriately designing metal sandwiches, we can make structures that should optimise their interaction. Our aim in this short sabbatical stay is to try out a new idea we have borrowed from another field in which we have successfully shown the largest optical nonlinearities ever produced, to try these out on plasmons.Today's commercial laser systems deliver reproducible pulses as short as 10 fs, making myriad applications possible in science, medicine, fabrication and communication. The world abounds in resonances, each material having specific wavelengths for enhanced light-matter interaction. Perhaps the single most important aspect of a laser is therefore the wavelength of the radiation, and means to control this are a top priority. Optical wavelength conversion or amplification of laser radiation is conventionally achieved by means of nonlinear optical effects in specific crystals, waveguides or periodically patterned media to obtain harmonic generation or optical parametric oscillation through second or third order optical nonlinear effects. When using nonlinear bulk crystals for such purposes it is essential to use a material which meets the optical phase matching conditions for optical nonlinear generation. The direction and polarization of incident light and the axis of the crystal must be strictly adjusted, as must be the temperature. When using optical waveguides or periodically patterned media in such applications to improve efficiency the tuning range for the output light is limited by the tight geometrical specifications required.A drastic reduction of both the size and the optical power consumption of conventional photonic devices based on nonlinear effects may be possible using the strong confinement of the electromagnetic field. One proposal for such confinement is the use of photonic crystal structures. However, these structures are expensive and subject to strict geometrical constraints in more than one dimension.We propose to achieve this confinement by exploiting the interaction of two SPPs for efficient optical wavelength conversion in a cheap, compact and simple structure. This method has the potential to be effective in a wide range of applications in optical modulation, optical amplification or optical frequency conversion. Its versatility and optical frequency-tunability should allow it to be applied to a variety of situations in scientific, industrial, and environmental applications. The method should prove very useful in conjunction with pulsed or continuous lasers to widen the optical frequency range obtainable, as a optical parametric amplifier. This provides at the same time a means to achieve the generation of a broadband spectrum of optical frequencies from a pulsed laser, for example a supercontinuum, with particularly important applications in medicine and ultrafast spectroscopy. Furthermore, the invention provides a means to modulate optical radiation from low frequencies up to ultrahigh frequencies up to and above the terahertz range. This should be a boon in ultrafast switching applications in future telecommunications systems. The invention should also find application inside analytical equipment, such as in laser spectrometers, laser ranging systems, remote sensing systems, imaging systems, and laser power delivery systems.