Physics and applications of a novel nanometer-sized femtosecond electron souce

该项目旨在了解和控制由近红外、中红外和远红外辐射的超短脉冲触发的尖锐金属针的高度非线性光电发射过程。在这个项目的第一个资助阶段，我们展示了从纳米结构获得一种新的光电子发射机制，其中电子的动能不再仅仅由光子能量和功函数决定，而是由电子与针尖局部增强的光学近场的相互作用决定。在第二个筹资阶段，一个主要目标是通过多种手段操纵这些过程，包括：(1)多个不同波长的脉冲，如太赫兹脉冲；(2)对载波包络相位的控制；(3)利用表面等离子体激元极化子场对电子脉冲进行选通。使用这些方法，我们计划在这个纳米结构上达到以前没有达到的对飞秒和阿秒电子动力学的控制水平，这将通过改变从激发区域发射的电子的角和动能分布来表现出来。除了研究发射和加速过程的基本性质外，我们还将继续努力应用这种具有高空间相干性的脉冲电子源。具体地说，我们将在点投影几何结构中，在纳米线和多层石墨烯上进行空间分辨电子能量损失谱实验。

The project aims at understanding and controlling highly nonlinear photoemission processes at sharp metallic needles triggered by ultrashort pulses of near-, mid- and far-infrared radiation. In the first funding phase of this project, we demonstrated access to a new regime in photoemission from nanostructures, in which the electrons’ kinetic energies are no longer determined by the photon energy and the work function alone, but rather by the interaction of the electrons with the locally enhanced optical near-field at the apex of the needles. In the second funding phase, a main objective lies in the manipulation of these processes by a number of means, including (i) multiple pulses of varying wavelength, such as THz pulses, (ii) control over the carrier-envelope phase and (iii) gating of electron pulses by means of surface plasmon polariton fields. Using these approaches, we plan to reach a previously unachieved level of control over the femtosecond and attosecond electron dynamics at this nanostructure, which will manifest itself in modifications of the angular and kinetic energy distributions of electrons emitted from the excitation region. In addition to the study of fundamental properties of the emission and acceleration process, we will extend the efforts regarding the application of this pulsed electron source with high spatial coherence. Specifically, we will experiment with spatially resolving electron energy loss spectroscopy on nanowires and multilayer graphene in a point-projection geometry.