Combintion of Scanning Electron- and Darkfield-Microsocopes to study electron-light interactions

我们小组对描述纳米光学系统以及极端水平上的自由电子-光相互作用很感兴趣。我们问自己，为了促进增强的电子-光相互作用，可以实现什么样的纳米系统，从而导致(I)在与电子束相互作用中产生相干光，(Ii)几乎确定的单光子产生，以及(Iii)动态电子光学。我们感兴趣的是设计与激光激发相结合的系统，在自由电子波包中导致量子相干的弹性和非弹性跃迁。在这个概念中，我们特别感兴趣的是探索所涉及的参数范围(如激光强度、极化和入射角、电子速度)，以寻找相互作用不能绝热描述的区域；因此，一套新的物理原理应运而生。例如，量子相干干涉可能是由于双光子过程−导致电子暂时失去平衡而发生的，这种方式使得单光子过程也可以满足动量匹配准则，而在正常情况下，单光子相互作用是被禁止的。此外，导致这种相互作用的量子相干路径可能会发生干涉；随后，观察到奇异的衍射图。特别是，我们希望设计纳米和微型结构，在与电子束相互作用时，在电子显微镜中充当相干光源。因此，将这些系统集成到电子显微镜中可以用于相关的电子光学显微镜和光谱学。为此，我们打算使用激子/等离子体混合系统，它通过等离子体和激子的强相互作用，既实现了相干极化，又实现了强电子诱导辐射。此外，我们的计划是实现研究动能从200 eV到亚10keV的慢电子波包与光和纳米结构相互作用的系统。与相对论电子相比，慢电子对电磁相互作用更敏感；因此，非绝热相互作用也更容易被触发。在这个项目中，激光脉冲将被用来激励场发射电子源，并产生单电子波包。将通过商用和自制的透射式电子探测器来研究光电子波包与光在显微镜腔中的相互作用。

Our group is interested in characterizing nanoptical systems as well as free-electron-light interactions at the extreme levels. We ask ourselves, what kind of nanosystems can be realized, in order to foster enhanced electron-light interactions, leading to (i) the generation of coherent light in interaction with electron beams, (ii) nearly deterministic single-photon generation, and (iii) dynamical electron optics. We are interested in designing systems that in combination with laser excitations, lead to quantum-coherent elastic and inelastic transitions in free-electron wavepackets. Within this concept, we are interested in particular, in exploring the domain of parameters involved (like laser intensity, polarization, and incidence angle, electron velocity), to seek for regions where the interactions cannot be described adiabatically; therefore, a whole set of new physical principles emerge. As an example, quantum coherent interferences might occur as a result of temporarily driving the electrons out of equilibrium thanks to two-photon processes − in such a way that momentum-matching criterion can be satisfied for single-photon processes as well, whereas in normal conditions, single-photon interactions are forbidden. Moreover, quantum-coherent paths leading to such interactions may interfere; subsequently, exotic diffraction patterns are observed. In particular, we would like to design nano- and micro-structures that in interaction with electron beams, act as coherent sources of light in electron microscopes. Therefore, incorporation of those systems in electron microscopes can serve for correlative electron-light microscopy and spectroscopy. For this purpose, we intend to used hybrid excitonic/plasmonic systems, which through strong interaction of plasmons and excitons, both coherent polarizations as well as strong electron-induced radiations are achieved. Additionally, our plan is to realize systems for investigating the interactions of slow-electron wavepackets, with kinetic energies ranging from 200 eV to sub-10 keV, with light and nanostructures. Slow electrons are more sensitive to the electromagnetic interactions in comparison with their relativistic counterparts; as a result, nonadiabatic interactions are also more easily triggered. Within this project, laser pulses will be used to excite a field-emission electron source and to generate single-electron wavepackets as well. Interaction of photoemission electron wavepackets with light in the microscopy chamber will be investigated by means of commercial and house-build transmission electron detectors.