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

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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.