介绍了表面等离子体激元的电磁场局域与放大效应对于非线性响应的增强机制。电磁波与金属中自由电子耦合所产生的表面等离子体激元，可使金属表面亚波长空间尺度内的电磁场能量密度得到增强，放大非线性效应幅度，降低非线性过程所需要的入射光强，实现纳米尺度内弱光非线性效应的产生。以纳米颗粒为例介绍表面等离子体激元共振对于电磁场及非线性增强的机理，同时介绍描述纳米复合材料有效非线性系数的有效非线性介质理论，并使用该理论分析表面等离子体激元场对于非对称裂环超材料有效非线性的调控能力，最后介绍了利用表面等离子体激元共振场实现对于非线性旋光效应的增强。利用等离子体激元增强非线性为实现纳米弱光非线性技术提供了一种很好的途径。

This paper is focused on an introduction to the mechanism of nonlinearity enhancement by field confinement and magnification effects of surface plasmon polariton (SPP). By coupling the incident electromagnetic field with the coherent motion of free-electron plasma in the metal, SPP is excited near the metal surface, providing field confinement in nanoscale, which results in the enhancement of electrical field and nonlinearity magnitude. The light intensity required for nonlinear process is dramatically reduced and the occurrence of weak light nonlinear process in nanoscale is possible. Starting from the situation of metallic nanoparticle system, the basic principle of enhancement of electric field and nonlinearity by surface plasmon resonance is introduced. A theory for the evaluation of third-order optical susceptibility of nonlinear nano-composites is presented, which is further used to analyze the nonlinear property of an asymmetric split ring metamaterial. Finally, the surface plasmon resonance is used to enhance the magnitude of nonlinear optical activity effect. The nonlinearity enhancement by surface plasmon is proved to pave a way for the development of weak light nonlinearity in nanoscale.