Femtosecond extreme ultraviolet (fs-XUV) source

飞秒极紫外源在这个建议中要求将是唯一的极紫外源的光电发射实验计划在组Experimentelle物理学VI，相干自旋现象的固体，目前正在建立在TU多特蒙德。该小组的主要目标是通过最小化能量耗散，即通过相干效应，在尽可能短的长度和时间尺度上控制固体的磁性和电子性质。特别是，飞秒极紫外光源将用于两个平行的实验方案：i）自旋和角度分辨光电子能谱，ii）飞行时间动量显微镜。这种组合将使我们能够进行尖端的自旋，角度和时间分辨的光电发射实验，这些实验计划在ERC合并项目hyControl和DFG合作研究中心TRR 160的项目B 9中进行：“定制半导体中相互作用自旋激发的相干操纵”。hyControl的主要目标是实现纳米级混合单元的相干控制，这些混合单元是通过在无机表面沉积分子单元而形成的。另一方面，项目B 9旨在磁有序2D材料中自旋的超快操纵。正在进行的研究项目，以及该小组计划的未来研究活动，对飞秒极紫外光源提出了一系列苛刻的要求。它应该是一个高功率（至少300 W）和高重复率（至少300 kHz）的Yb基放大激光系统，同时服务于两个泵浦-探测装置。高功率确保了并行可操作性，而高重复率允许以高信噪比执行光电发射实验，同时规避空间充电效应，空间充电效应通常会降低时间分辨光电发射实验中的能量和动量分辨率。在每个泵浦-探测线中，泵浦光束将由光学参量放大器产生，而探测光束将由能量高达70 eV的极紫外飞秒光子组成。需要高光子能量来映射所研究的材料在整个布里渊区的能带结构。此外，在分子系统中，极紫外光谱范围是必要的，以执行分子轨道映射，增强横截面和解开的光电发射功能的分子从那些基板。飞秒极紫外脉冲的产生需要不同的组件-主要是一个放大的激光系统连接到惰性气体和几个压缩级中的高次谐波产生装置。这些组件需要彼此完美地调整，以实现所需的规格。只有当整个系统由一家公司提供时，这一结果才能在实践中得到保证。

The femtosecond extreme ultraviolet source requested in this proposal will be the only extreme ultraviolet source for the photoemission experiments planned in the group Experimentelle Physik VI, coherent spin phenomena in solids that is currently being established at the TU Dortmund. The main goal of the group is to control the magnetic and electronic properties of solids on the shortest possible length- and time-scales by minimizing energy dissipations, i.e. by means of coherent effects. In particular, the femtosecond extreme ultraviolet source will be employed in two parallel experimental schemes: i) spin- and angle-resolved photoemission spectroscopy, ii) time-of-flight momentum microscopy. This combination will allow us to perform the cutting-edge spin-, angle- and time-resolved photoemission experiments that are planned in the ERC consolidator project hyControl and in the project B9 of the DFG Collaborative Research Centre TRR 160: “Coherent manipulation of interacting spin excitations in tailored semiconductors” as well. The main goal of hyControl is to achieve coherent control of nano-scale hybrid units that are formed by depositing molecular units on inorganic surfaces. On the other hand, project B9 aims at the ultrafast manipulations of spins in magnetically ordered 2D materials. The on-going research projects, as well as future research activity planned in the group, pose a set of demanding requirements on the femtosecond extreme ultraviolet source. It should be a high power (at least 300 W) and high repetition rate (at least 300 kHz) Yb-based amplified laser system serving simultaneously two pump-probe set-ups. The high power ensures in-parallel operability, while the high repetition rate allows to perform photoemission experiments with high signal-to-noise ratio while circumventing space-charging effects, which typically reduce the energy- and momentum-resolution in time-resolved photoemission experiments. In each pump-probe line the pump beam will be generated by an optical parametric amplifier, while the probe beam will consist of extreme ultraviolet femtosecond photons with energy up to 70 eV. The high photon energies are required to map the band structure of the studied materials throughout the whole Brillouin zone. In addition, in molecular systems, the extreme ultraviolet spectral range is necessary to perform molecular orbital mapping, enhance the cross section and disentangle the photoemission features of the molecules from those of the substrate. The generation of femtosecond extreme ultraviolet pulses requires different components – mainly an amplified laser system connected to a setup for high harmonic generation in noble gases and several compression stages. Such components need to be perfectly tuned with each other in order to achieve the required specifications. This result can be in practice guaranteed only if the whole system is provided by a single company.