Nonlinear Plasmonics

摘要：非线性晶体中有效的光频转换是通过相位匹配来实现的--非线性响应在晶体中传播时的相干相加。今天，从激光聚变到激光指示器，光学频率转换在许多领域都得到了应用。然而，为了进行相位匹配，晶体需要有多个波长的尺寸，这与纳米级的架构不兼容。因此，强烈的局部非线性响应依赖于固有的材料非线性。这项研究计划研究由贵金属如金和银制成的等离子体纳米结构的高光学非线性。这些结构使得在移动的频率下产生局部光成为可能，并且可以利用纳米器件中的多光谱相互作用，而不需要相位匹配。本研究计划研究离散的和定义明确的金属纳米结构的非线性响应，例如纳米颗粒、纳米棒和粒子杂化(二聚体、三聚体)。这些结构起到了光学天线的作用--它们使入射场局部化和增强，并有助于释放非线性响应。目标是识别、理解和利用产生高非线性效率的配置。许多非线性相互作用，如谐波频率产生或非线性四波混频，都是相干过程，因此局域场的相敏相互作用对于强响应是重要的。研究人员研究频率转换场与单个量子发射体的相互作用，如量子点、分子或离子。通过非线性过程在局部产生光的能力为纳米光子学和活性等离子体子学提供了新的机会。

ABSTRACT:Efficient optical frequency conversion in nonlinear crystals is made possible by phase matching - the coherent addition of the nonlinear response upon propagation through the crystal. Today, optical frequency conversion is exploited in many areas, ranging from laser fusion to laser pointers. However, in order for phase matching to occur a crystal needs to be many wavelengths in size, which is not compatible with nanoscale architectures. A strong local nonlinear response therefore relies on intrinsic material nonlinearities. This research program investigates the high optical nonlinearities of plasmonic nanostructures made of noble metals such as gold and silver. These structures make it possible to generate light locally at shifted frequencies and to exploit multispectral interactions in nanoscale devices, without the need of phase matching.This research program investigates the nonlinear response of discrete and well-defined metal nanostructures, such as nanoparticles, nanorods and particle hybrids (dimers, trimers). These structures function as optical antennas - they localize and enhance the incident fields and they facilitate the release of the nonlinear response. The goal is to identify, understand and exploit configurations that yield high nonlinear efficiencies. Many nonlinear interactions, such as harmonic frequency generation or nonlinear four-wave mixing, are coherent processes and hence the phase-sensitive interplay of local fields is important for a strong response. The investigators study the interaction of frequency-converted fields with single quantum emitters, such as quantum dots, molecules, or ions. The ability to generate light locally through nonlinear processes provides new opportunities for nanophotonics and active plasmonics.