{'fraction_non_alphanumeric': 0.03643173306094655, 'fraction_numerical': 0.014300306435137897, 'mean_word_length': 5.032854209445585, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Ultrafast dynamics of nanoparticles in highly intense X-Ray pulses

With the advent of X-ray free electron laser, such as the Linac Coherent Light Source (LCLS), structural studies on non-repetitive and non-reproducible nanoparticles, such as single biomolecules appear imminent. A key challenge to increasing the resolution of single particle imaging is radiation damage. Only a sound understanding of the underlying damage processes, such as the nanoplasma expansion, can overcome this challenge and will lead to higher spatial resolutions. As possibility to achieve higher resolutions, sacrificial layers have been proposed to slow the nanoplasma expansion. This thesis investigates nanoplasma formation and expansion in superfluid He-, bulk Xeand heterogeneous HeXe-clusters, whereby HeXe-clusters are testbed nanoparticles for sacrificial layers. The clusters are generated through a supersonic gas expansion into a vacuum and investigated using an ultrafast X-ray pump–X-ray probe technique from the LCLS. A first Xray pulse with 1.5 nm wavelength triggers the nanoplasma evolution and reaches intensities of ∼2 · 1016 W cm−2. A second X-ray probe-pulse, with power densities of ∼2 · 1017 W cm−2 at 1.5 nm wavelength, creates diffraction images of the nanoplasma at a later time, ∆t. ∆t is varied between (0 to 800) fs and furthermore ion-spectra are captured via time-of-flight (TOF) mass spectroscopy. The experiment was performed at the Atomic, Molecular, and Optical physics (AMO) instrument using the so-called “LAMP” end-station at LCLS. The LAMP end-station was partly designed, built, and operated as part of this thesis work. The study reveals single-shot diffraction images and TOF spectra of Xe-, Heand HeXe-clusters with unprecedented resolution, for example, the reconstruction of a∼25 nm radius Xe-cluster with ∼6 nm resolution is shown. The diffraction images and corresponding reconstructions show the nanoplasma formation and expansion of those clusters. An analysis of several hundred diffraction images suggests that the initial Xe-cluster radius increases by ∼20 % over 800 fs. Therefore, the expansion-speed is ∼15 250 m s−1, and the electron temperature is ∼125 eV. Reconstructions and 2D computer models of few-hundred nanometer radius HeXe-clusters indicate that they agglomerate similar to a plum-pudding model, as Xe-atoms condense to multiple small clusters within the He-droplet. TOF spectra strongly imply that the Xe-clusters transfer kinetic energy to the sacrificial layer and that the He-layer supplies electrons to the ionized Xe-clusters. Diffraction images and 2D computer models of HeXe-clusters show that encapsulated Xe-clusters do not exhibit detectable damage in the initial 800 fs, while the He-layer undergoes an expansion. As a measure of the effectiveness of the sacrificial layer, the radiation damage of pristine Heand Xe-clusters, as well as HeXe-clusters are compared to each other.