Abstract
Focusing hard x-ray free-electron laser radiation with extremely high fluence sets stringent demands on the x-ray optics. Any material placed in an intense x-ray beam is at risk of being damaged. Therefore, it is crucial to find the damage thresholds for focusing optics. In this paper we report experimental results of exposing tungsten and diamond diffractive optics to a prefocused 8.2 keV free-electron laser beam in order to find damage threshold fluence levels. Tungsten nanostructures were damaged at fluence levels above 500 mJ/cm(2). The damage was of mechanical character, caused by thermal stress variations. Diamond nanostructures were affected at a fluence of 59 000 mJ/cm(2). For fluence levels above this, a significant graphitization process was initiated. Scanning Electron Microscopy (SEM) and µ-Raman analysis were used to analyze exposed nanostructures.
Highlights
New high-brightness hard x-ray free-electron laser (XFEL) facilities offer radiation with femtosecond pulse duration and exceptional coherence enabling novel and exciting experiments in a variety of scientific fields [1,2,3]. The brightness of these new sources is far superior than any other one that is currently available, it is in many experiments important to focus the XFEL beam down to spot diameters in the nanometer regime; especially coherent x-ray imaging of single particles, xray absorption spectroscopy, or nonlinear optics in the hard x-ray regime
The extremely high fluence imposed on zone plates from an XFEL beam can be problematic
In this paper we present experimental results from the Linac Coherent Light Source (LCLS) where tungsten and diamond diffractive optics were exposed to an 8.2 keV, prefocused XFEL beam, demonstrating at what fluence levels each of the optics degrades
Summary
New high-brightness hard x-ray free-electron laser (XFEL) facilities offer radiation with femtosecond pulse duration and exceptional coherence enabling novel and exciting experiments in a variety of scientific fields [1,2,3]. The brightness of these new sources is far superior than any other one that is currently available, it is in many experiments important to focus the XFEL beam down to spot diameters in the nanometer regime; especially coherent x-ray imaging of single particles (high resolution), xray absorption spectroscopy (fluence), or nonlinear optics in the hard x-ray regime (peak intensity). There are different types of x-ray optics available which are based on different physical mechanisms like, e.g., diffraction, refraction, or reflection of x-rays [4,5,6]. Any structural changes in the zone plate material, caused directly by ionizing radiation or heating through absorption, could result in a decreased performance or even failure of the device
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