Investigation and application of soft X-ray emission from targets containing micron-sized liquid droplets irradiated with intense laser pulses

极端紫外线(XUV)和软X射线(SXR)光谱区域对于一系列科学问题具有突出的相关性。一方面，这是由于极短的波长能够实现高空间分辨率。另一方面，这是由于物质在这一光谱范围内的特征吸收行为，这使得能够识别元素组成甚至化学环境。由于其高亮度和多功能性，同步加速器以及后来的自由电子激光注定了这一科学领域的命运。然而，研究人员正在积极寻找替代的XUV和SXR辐射源，以便提供更灵活的进入软X射线区域的途径。尤其是激光驱动的光源，在过去已经取得了几项突破。例如，13.5纳米技术目前在光刻领域站稳了脚跟，但仍在与碎片有关的巨大挑战作斗争。到目前为止，还没有令人信服的解决方案来获得明亮的、同时具有成本效益的XUV和SXR辐射源，特别是在操作成本方面。波兰同事提出了一种很有希望的方法，即使用智能的同轴双喷嘴布置来产生高度准直的密集靶光束，在此基础上，将研究这种喷嘴的新变种，以产生极宽的SXR辐射。虽然到目前为止使用的是原子和分子气体，但现在也将使用团簇和气溶胶，从而实现更高的目标密度。这将带来更高的效率和更宽的频谱。一种特别有希望的方法是将重元素溶解在要雾化的液体中。波兰队和德国队有许多不同的激光，脉冲参数非常不同。与理论建模相结合，这些能够对新目标进行系统研究，包括特征。这两项研究都是由合作中的两个科学应用驱动的，这两个科学应用将在项目框架内推进。一方面，这是一种新的纳米级断层成像方法，它建立在相干层析成像的基础上，依赖于宽带辐射的可用性。与迄今使用的高次谐波辐射不同，该项目将进入SXR制度。因此，例如磁性材料的更高空间分辨率和特别有趣的光谱范围将可用于基于实验室的研究。为此，成像将得到X射线吸收精细结构光谱(XAFS)的补充。这使得能够非破坏性地获得样品内部结构的信息，包括其成分和化学环境。

The extreme ultraviolet (XUV) and soft X-ray (SXR) spectral region is of outstanding relevance for a manifold of scientific questions. On the one hand, this is due to the extremely short wavelength enabling high spatial resolution. On the other hand, it is due to the characteristic absorption behavior of matter in this spectral regime, which enables the identification of the elemental composition and even the chemical environment. By virtue of their high brilliance and versatility, synchrotrons and, latterly, free-electrons lasers are predestined for this field of science. Nevertheless, researchers are vigorously seeking for alternative XUV and SXR radiation sources, inter alia, in order to provide a more flexible access to the soft X-ray region. Particularly laser-driven sources have seen several breakthroughs in the past. For example, the 13.5-nm technology currently establishes itself in lithography, however still fighting massive challenges concerning debris. So far, there is no convincing solution for a brilliant and, at the same time, cost-effective XUV and SXR radiation source, particularly also with respect of operation costs.Building on a promising approach of the Polish colleagues, which uses a smart coaxial double-nozzle arrangement to generate a well-collimated dense target beam, novel variants of this nozzle will be investigated in order to generate extremely broadband SXR radiation. While atomic and molecular gases were used so far, now also cluster and aerosols will be employed, thus achieving much higher target densities. This will lead to higher efficiency and broader spectra. A particularly promising approach is to dissolve heavy elements in the liquids to be atomized. The Polish and German teams have available a number of different lasers with very different pulse parameters. Together with theoretical modeling, these enable systematic research on the new target, including characterization.Above research is driven by two scientific applications within the collaboration, which will be advanced in the framework of the project. On the one hand, this is a novel method for nanoscale cross-sectional imaging, which rests on coherence tomography and depends on the availability of broadband radiation. In contrast to high-harmonic radiation that has been used so far, this project will give access to the SXR regime. As a consequence, higher spatial resolution and a particularly interesting spectral range for, e.g., magnetic materials will become available for lab-based research. To this end, imaging will be complemented by X-ray absorption fine-structure spectroscopy (XAFS). This enables to non-destructively gain information of the internal structure of samples including their composition and chemical environment.