51 research outputs found
Unsupervised real-world knowledge extraction via disentangled variational autoencoders for photon diagnostics
We present real-world data processing on measured electron time-of-flight
data via neural networks. Specifically, the use of disentangled variational
autoencoders on data from a diagnostic instrument for online wavelength
monitoring at the free electron laser FLASH in Hamburg. Without a-priori
knowledge the network is able to find representations of single-shot FEL
spectra, which have a low signal-to-noise ratio. This reveals, in a directly
human-interpretable way, crucial information about the photon properties. The
central photon energy and the intensity as well as very detector-specific
features are identified. The network is also capable of data cleaning, i.e.
denoising, as well as the removal of artefacts. In the reconstruction, this
allows for identification of signatures with very low intensity which are
hardly recognisable in the raw data. In this particular case, the network
enhances the quality of the diagnostic analysis at FLASH. However, this
unsupervised method also has the potential to improve the analysis of other
similar types of spectroscopy data
Role of heat accumulation in the multi-shot damage of silicon irradiated with femtosecond XUV pulses at a 1 MHz repetition rate
The role played by heat accumulation in multi-shot damage of silicon was studied. Bulk silicon samples were exposed to intense XUV monochromatic radiation of a 13.5 nm wavelength in a series of 400 femtosecond pulses, repeated with a 1 MHz rate (pulse trains) at the FLASH facility in Hamburg. The observed surface morphological and structural modifications are formed as a result of sample surface melting. Modifications are threshold dependent on the mean fluence of the incident pulse train, with all threshold values in the range of approximately 36-40 mJ/cm<sup>2</sup>. Experimental data is supported by a theoretical model described by the heat diffusion equation. The threshold for reaching the melting temperature (45 mJ/cm<sup>2</sup>) and liquid state (54 mJ/cm<sup>2</sup>), estimated from this model, is in accordance with experimental values within measurement error. The model indicates a significant role of heat accumulation in surface modification processes
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CAMP@FLASH: an end-station for imaging, electron- and ion-spectroscopy, and pump–probe experiments at the FLASH free-electron laser
The non-monochromatic beamline BL1 at the FLASH free-electron laser facility at DESY was upgraded with new transport and focusing optics, and a new permanent end-station, CAMP, was installed. This multi-purpose instrument is optimized for electron- and ion-spectroscopy, imaging and pump–probe experiments at free-electron lasers. It can be equipped with various electron- and ion-spectrometers, along with large-area single-photon-counting pnCCD X-ray detectors, thus enabling a wide range of experiments from atomic, molecular, and cluster physics to material and energy science, chemistry and biology. Here, an overview of the layout, the beam transport and focusing capabilities, and the experimental possibilities of this new end-station are presented, as well as results from its commissioning
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