可见光波在天然金属基界面正负折射机理的研究和进展

Recent Progress of the Researches on the Positive and Negative Refractions of the Visible Light Propagating at the Metal-based Interface

Snell定律揭示了光在穿越不同介质界面时的传播和折射规律,这是现代物理光学的重要基础。追求完美光学透镜的途径之一是寻找正负折射率匹配材料,但在相当长时期内,在自然界中从未发现有违背Snell定律的天然负折射率材料存在。在本研究工作中制备了一系列入射角精确可控的楔形贵金属金和银等样品,采用不同波长的激光,对于光在最简单的天然贵金属界面传播时所发生的由负到正折射特性变化进行了定量实验测量,获得表观折射率随入射和折射角变化的定量关系。对于导致奇异光折射现象的各种争议性机理进行了细致探索和讨论,这与等离子体、负磁导率和Goos-Hanchen等效应无关。研究结果将有助于人们理解光在金属基微结构中发生正负折射传播的物理机理,从而为新型微纳光电子材料和器件的研制和应用建立基础。

Snell＇s law reveals the propagation and refraction properties of the light when it passes through the interface composed by two media with different optical constants. It is the foundation of modem physical and geometrical optics. The effort to realize a perfect lens is trying to find the material with a negative refractive index, which has not yet been found in the natural material in past years. In this work, we have fabricated a series of noble-metal-based film samples （Au and Ag） with different incident angles. We quantitatively measured the refraction of the light passing through the metal/air interface, and observed that the refraction can change from negative to positive in the visible range at the simplest natural metal/air interface. The mecha- nisms for causing the negative refraction have been carefully discussed and analyzed, and are not attributed to the effects, such as the plasmon resonance, the negative permeability, the Goos-Hanchen shift, and so on. We hope, therefore, the results given in this work will stimulate people to understand more of the physical origin of the negative refraction happened in the metal-based artificial materials, and will help its application in the photonics material and device design and fabrication in the future.