Proceedings Article | 14 May 2019
Tomáš Burian, Vera Hájková, Libor Juha, Karel Saksl, Vojtech Vozda, Igor Makhotkin, Eric Louis, Siegfried Schreiber, Kai Tiedtke, Sven Toleikis, Barbara Keitel, Elke Plönjes, Mabel Ruiz-Lopez, Marion Kuhlmann, Thomas Wodzinski, Hartmut Enkisch, Martin Hermann, Sebastian Strobel, Rolf Loch, Ryszard Sobierajski, Iwanna Jacyna, Dorota Klinger, Marek Jurek, Jerzy Pelka, Gosse de Vries, Michael Störmer, Frank Scholze, Frank Siewert, Tobias Mey, Jaromír Chalupský
KEYWORDS: X-rays, Optical filters, X-ray lasers, Free electron lasers, Laser ablation, Aluminum, Silicon, Signal attenuation, Extreme ultraviolet, Metals
An accurate transmission measurement of thin foils (usually made of elemental metals and/or semiconductors), which routinely are used as attenuators in soft x-ray beamlines, end-stations and instruments, represents a long standing problem over the wide experimentation field with photon beams, see for example [1-4]. Such foils are also frequently utilized for blocking long wavelength emission, i.e., UV-Vis-IR radiation, from plasma and high order harmonic sources, whilst soft x-rays emitted from the source pass through the foil with only a slight attenuation. Despite the enormous amount of data available in the literature, e.g., Henke’s tables [5], measurements made on real foils often provide surprising results. In this study, a procedure based on the ablation imprints method is utilized for determination of soft x-ray filter transmission, namely the f-scan technique [6,7]. This technique combines the GMD (Gas Monitor Detector) pulse energy measurement and attenuation of the beam by foils (made of different metallic/semiconducting elements of varying thickness) with areas of ablation imprints created on a suitable target, e.g. PMMA – Poly(methyl methacrylate). The results show only a partial overlap with transmission values found in Henke’s tables. Nevertheless, a good agreement with transmission values determined by conventional radiometry techniques at synchrotron radiation beamlines has been found. Such a difference between the experimentally obtained values and transmissions calculated for a pure element is usually explained by spontaneous formation of oxidized layers on the filter surface and in the near-surface layer and their possible alteration by intense FEL radiation. The first results obtained with Al, Nb, Zr and Si filters at FLASH/FLASH2 (Free-electron LASer in Hamburg tuned to 13.5 nm) facilities will be shown and discussed in this presentation.
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