Ultrafast nanooptics: Plasmon Coupling, Propagation, and Interference on the Nanoscale, using femtosecond photoemmission microscopy

将光耦合到金属结构中，并引导、操纵和转换回光是非常可取的，因为这将彻底改变现代电信和计算技术。然而，金属中的光学损耗太大，不能直接传输光，光必须转换成表面等离子激元（SPP），即在金属表面和周围介质之间的界面传播的电荷密度波。在他之前的工作中，申请人开发了一种利用双光子光电发射显微镜（2PPE PEEM）在Ag岛表面可视化SPP波的技术。2PPE PEEM依靠飞秒（fs）激光脉冲照射表面，并提供具有视频速率的等离子体增强非线性光电发射图像。在第一个资助期内，申请人证明了2PPE PEEM可以用于研究SPP在fs激光脉冲下的激发，可以观察到SPP的传播，并且2PPE PEEM适用于研究SPP回光的耦合。通过在银岛表面覆盖数nm的C60， SPP的性能逐渐发生变化。本建议旨在对SPP的传播和与物质的相互作用有一个基本的认识。在2PPE PEEM中新开发的正入射（NI）几何中，等离子体相关的对比度提供了传播SPP的更详细的图像。在泵浦探针实验中使用NI，应该可以直接观察SPP波包，当它穿过表面，被反射或转换回光时。利用SPP干涉和控制不同偏振的泵浦脉冲和探测脉冲之间的相移，可以控制岛屿后的光学近场，其分辨率接近衍射极限。

The coupling of light into metallic structures, and the guiding, manipulation, and conversion back into light is extremely desirable, because this would revolutionize modern telecommunication and computing technology. The optical losses in metals are too large to transport light directly, however, and the light must be converted into a surface plasmon polariton (SPP), i.e., a charge-density wave that propagates at the interface between the metallic surface and the surrounding medium. In his previous work, the applicant has developed a technique to visualize SPP waves at the surface of Ag islands with two photon photoemission microscopy (2PPE PEEM). 2PPE PEEM relies on femtosecond (fs) laser pulses for illumination of the surface and provides plasmon-enhanced nonlinear photoemission images with video rate. During the first funding period, the applicant demonstrated that 2PPE PEEM can be used to study the excitation of SPPs with fs laser pulses, that SPP propagation can be observed, and that 2PPE PEEM is suitable to study the coupling of SPPs back into light. By covering the surface of an Ag island by only a few nm C60, the properties of the SPP were gradually changed. The present proposal aims at a fundamental understanding of the SPP propagation and interaction with matter. In the newly developed normal incidence (NI) geometry in 2PPE PEEM, the plasmon-related contrast provides a more detailed picture of the propagating SPP. Using NI in a pump-probe experiment, it should be possible to observe a SPP wave packet directly while it travels across the surface, is reflected, or is converted back into light. Using SPP interference and controlled phase shifts between pump and probe pulses of different polarizations, the optical near field behind the islands will be controlled with a resolution close to the diffraction limit.