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The transmission of the optical components of the Bernina branch of the Aramis beamline at SwissFEL has been measured with an X-ray gas monitor from DESY and compared with a PSI gas detector upstream of the optical components. The transmission efficiencies of the mirrors and the various other in-beam components were evaluated and compared with theoretical calculations., The transmission of the optical components of the Bernina branch of the Aramis beamline at SwissFEL has been measured with an X-ray gas monitor from DESY and compared with a PSI gas detector upstream of the optical components. The transmission efficiencies of the Mo, Si and SiC mirror coatings of the Aramis beamline and the various other in-beam components were evaluated and compared with theoretical calculations, showing an agreement of 6% or better in all cases. The experiment has also shown the efficacy of the high-harmonic rejection mirrors at the Bernina branch of the Aramis beamline at SwissFEL, and characterized the transmission efficiency of the on-line spectrometer in the Aramis beamline. The theoretical transmission of the mirror coatings match the experimental data to within 7%. The accuracy of these measurements was checked against a radiative bolometer from a Japanese collaboration and found to agree to a level of 4% or better. Further comparisons with a diamond detector from a US-based inter-institute collaboration demonstrated a good agreement for the attenuator settings of the beamline.

Physical review applied 14(3), 034057 (2020). doi:10.1103/PhysRevApplied.14.034057, Solids irradiated by energetic photons can be eroded in two modes, depending on the radiation intensity. High average, low-peak power sources, e.g., synchrotron radiation and high-order harmonics, induce desorption of the material at a low etch rate. In contrast, high-peak-power radiation from extreme ultraviolet and x-ray lasers usually causes a massive removal of the material even by a single shot. In this contribution, an effective material erosion is reported in PMMA exposed to multiple accumulated pulses generated by the free-electron x-ray-laser Linac Coherent Light Source (LCLS, tuned at a photon energy of 830 eV in this study, operated in Menlo Park at Stanford, CA, USA) at a fluence below the single-pulse ablation threshold. The effect is caused by polymer-chain scissions initiated by single photons carrying enough energy to break the C$—$C bounds. High efficiency of the erosion is supposed to occur due to a correlation of the single-photon effects. The subthreshold damage exhibits a nonlinear dose dependence resulting from a competition between chain scissions and cross-linking processes. The cross-linking is proven by Raman spectroscopy of the irradiated polymer. Two theoretical models of the x-ray free-electron-laser-induced erosion are suggested, which provide an excellent agreement with the experimental results., Published by American Physical Society, College Park, Md. [u.a.]

Nature photonics 14(6), 391 - 397 (2020). doi:10.1038/s41566-020-0607-z, The European XFEL is a hard X-ray free-electron laser (FEL) based on a high-electron-energy superconducting linear accelerator. The superconducting technology allows for the acceleration of many electron bunches within one radio-frequency pulse of the accelerating voltage and, in turn, for the generation of a large number of hard X-ray pulses. We report on the performance of the European XFEL accelerator with up to 5,000 electron bunches per second and demonstrating a full energy of 17.5 GeV. Feedback mechanisms enable stabilization of the electron beam delivery at the FEL undulator in space and time. The measured FEL gain curve at 9.3 keV is in good agreement with predictions for saturated FEL radiation. Hard X-ray lasing was achieved between 7 keV and 14 keV with pulse energies of up to 2.0 mJ. Using the high repetition rate, an FEL beam with 6 W average power was created., Published by Nature Publ. Group, London [u.a.]

Journal of synchrotron radiation 26(4), 1045 - 1051 (2019). doi:10.1107/S1600577519003795, X-ray gas monitors (XGMs) are operated at the European XFEL for non-invasive single-shot pulse energy measurements and average beam position monitoring. They are used for tuning and maintaining the self-amplified spontaneous emission (SASE) operation and for sorting single-shot experimental data according to the pulse-resolved energy monitor data. The XGMs were developed at DESY based on the specific requirements for the European XFEL. In total, six XGM units are continuously in operation. Here, the main principle and experimental setup of an XGM are summarized, and the locations of the six XGMs at the facility are shown. Pulse energy measurements at 0.134 nm wavelength are presented, exceeding 1 mJ obtained with an absolute measurement uncertainty of 7–10%; correlations between different XGMs are shown, from which a SASE1 beamline transmission of 97% is deduced. Additionally, simultaneous position measurements close to the undulator and at the end of the tunnel are shown, along with the correlation of beam position data simultaneously acquired by an XGM and an imager., Published by Wiley-Blackwell, [S.l.]

X-Ray Free-Electron Lasers: Advances in Source Development and Instrumentation V : [Proceedings] - SPIE, 2019. - ISBN 97815106274209781510627437 - doi:10.1117/12.2520827 X-Ray Free-Electron Lasers: Advances in Source Development and Instrumentation, Prague, Czech Republic, 1 Apr 2019 - 4 Apr 2019; SPIE 1103810 pp. (2019). doi:10.1117/12.2520827, The absolute power of the Linac Coherent Light Source pulses has been measured accurately in the hard X-raybeamline by using simultaneously two detectors:1 an X-ray Gas Monitor Detector (XGMD)2 in tandem witha radiometer.3 From these measurements, we were also able to characterize and calibrate in details our setsof beamline attenuators, in addition to extending an absolute calibration for our beamline intensity monitors.Similarly, we demonstrate that commercial optical power meter has a response in the hard X-ray regime, thatcan be cross-correlated with the absolute power of the LCLS beam., Published by SPIE

Journal of synchrotron radiation 26(2), 320 - 327 (2019). doi:10.1107/S1600577519000250, Published by Wiley-Blackwell, [S.l.]

Journal of synchrotron radiation 26(5), 1422 - 1431 (2019). doi:10.1107/S1600577519006611, Published by Wiley-Blackwell, [S.l.]

A gas monitor detector was implemented and characterized at the Soft X-ray Research instrument (SXR) to measure the average, absolute and pulse-resolved photon flux of the LCLS beam in the energy range between 280 and 2000 eV., A gas monitor detector was implemented and characterized at the Soft X-ray Research (SXR) instrument to measure the average, absolute and pulse-resolved photon flux of the LCLS beam in the energy range between 280 and 2000 eV. The detector is placed after the monochromator and addresses the need to provide reliable absolute pulse energy as well as pulse-resolved measurements for the various experiments at this instrument. This detector provides a reliable non-invasive measurement for determining flux levels on the samples in the downstream experimental chamber and for optimizing signal levels of secondary detectors and for the essential need of data normalization. The design, integration into the instrument and operation are described, and examples of its performance are given.

The absolute single-shot pulse energy of the SPring 8 extreme ultraviolet (EUV) free electron laser (FEL) was measured using a cryogenic radiometer with a relative standard uncertainty of 3%. The temperature change of the cavity in the cryogenic radiometer caused by an incident FEL pulse was determined using a lock-in amplifier and an ac Wheatstone bridge. The measured pulse energies were compared with a gas-monitor detector developed by Physikalisch-Technische Bundesanstalt/Deutsches Elektronen-Synchrotron/Ioffe Physico-Technical Institute (Ioffe) at a wavelength of 51.3 nm at the SPring-8 EUV-FEL in a shot-to-shot mode. The pulse energies measured using the two detectors agree within 2.0%.

Objective: To assess if clinical features, prion protein codon 129, and molecular subtype correlate with MRI basal ganglia hyperintensity in sporadic Creutzfeldt-Jakob disease (CJD). Methods: The authors studied 219 patients including 153 confirmed CJD cases for their neurologic symptoms and MRI findings. The MRI was assessed by a blinded investigator for the presence of high signal intensity on T2-weighted images in the basal ganglia. Results: Patients with basal ganglia high signal on T2-weighted images were more likely to present with rapid progressive dementia in an early stage and shorter disease duration (median 6.7 months and 8.6 months). Surprisingly, among the CJD cases, patients without signal increase of the basal ganglia were shown to have a higher frequency of extrapyramidal disturbances (82% vs 70%). More striking differences were found for symptoms such as depression and sensory disturbances, which were more frequent among cases without signal increase. MRI was more likely to be diagnostic in patients with MV2 molecular subtype. Conclusions: Selected clinical and pathologic features correlate with the presence of basal ganglia high signal on T2-weighted MRI in patients with definite or probable CJD.

A nondestructive radiation detector unit is under construction at the TESLA Test Facility at DESY providing monitoring of the radiation (pulse energy, transverse intensity distribution, and statistical properties). The concept of the detector design is based on experience obtained during operation of TTF FEL, Phase 1. Key element of the detector is a wide dynamic range micro-channel plate (MCP) which detects scattered radiation from a thin gold wire crossing photon beam. Operating wavelength range of the detector is from 6 to 100 nm . An important feature of the MCP-based detector is that it is capable to cover all dynamic range of the radiation intensity, from the level of spontaneous emission up to the saturation level of SASE FEL.

This paper reports novel measurements of x-ray optical radiation on an absolute scale from the intense and ultra-short radiation generated in the soft x-ray regime of a free electron laser. We give a brief description of the detection principle for radiation measurements which was specifically adapted for this photon energy range. We present data characterizing the soft x-ray instrument at the Linac Coherent Light Source (LCLS) with respect to the radiant power output and transmission by using an absolute detector temporarily placed at the downstream end of the instrument. This provides an estimation of the reflectivity of all x-ray optical elements in the beamline and provides the absolute photon number per bandwidth per pulse. This parameter is important for many experiments that need to understand the trade-offs between high energy resolution and high flux, such as experiments focused on studying materials via resonant processes. Furthermore, the results are compared with the LCLS diagnostic gas detectors to test the limits of linearity, and observations are reported on radiation contamination from spontaneous undulator radiation and higher harmonic content.

For the proof-of-principle experiment of self-amplified spontaneous emission (SASE) at short wavelengths on the VUV FEL at DESY a multi-facetted photon beam diagnostics experiment has been developed employing new detection concepts to measure all SASE specific properties on a single pulse basis. The present setup includes instrumentation for the measurement of the energy and the angular and spectral distribution of individual photon pulses. Different types of photon detectors such as PtSi-photodiodes and fast thermoelectric detectors based on YBaCuO-films are used to cover some five orders of magnitude of intensity from the level of spontaneous emission to FEL radiation at saturation. A 1 m normal incidence monochromator in combination with a fast intensified CCD camera allows to select single photon pulses and to record the full spectrum at high resolution to resolve the fine structure due to the start-up from noise.

At the new SPring-8 extreme ultraviolet free-electron laser in Japan, a radiometric comparison between a gas-monitor detector from Physikalisch-Technische Bundesanstalt/Deutsches Elektronen-Synchrotron/Ioffe Physico-Technical Institute (Ioffe) and a cryogenic radiometer from National Institute of Advanced Industrial Science and Technology was carried out. Radiant power in the range between 30 µW and 350 µW was measured at the wavelengths of 51.3 nm, 56.1 nm and 61.2 nm. The results obtained with the two different detectors agree within 2.6%, which is well below their combined relative standard uncertainty, which varies from 4.1% to 5.5%.

Single shot radiation damage of bulk silicon induced by ultrashort XUV pulses was studied. The sample was chosen because it is broadly used in XUV optics and detectors where radiation damage is a key issue. It was irradiated at FLASH facility in Hamburg, which provides intense femtosecond pulses at 32.5 nm wavelength. The permanent structural modifications of the surfaces exposed to single shots were characterized by means of phase contrast optical microscopy and atomic force microscopy. Mechanisms of different, intensity dependent stages of the surface damage are described.

We have developed different types of photodetectors that are based on the photoionization of a gas at a low target density. The almost transparent devices were optimized and tested for online photon diagnostics at current and future x-ray free-electron laser facilities on a shot-to-shot basis with a temporal resolution of better than 100 ns. Characterization and calibration measurements were performed in the laboratory of the Physikalisch-Technische Bundesanstalt at the electron storage ring BESSY II in Berlin. As a result, measurement uncertainties of better than 10% for the photon-pulse energy and below 20 μm for the photon-beam position were achieved at the Free-electron LASer in Hamburg (FLASH). An upgrade for the detection of hard x-rays was tested at the Sub-Picosecond Photon Source in Stanford.

BACKGROUND AND PURPOSE: MR imaging has played an increasingly important role in the diagnosis of Creutzfeldt-Jakob disease (CJD) since basal ganglia abnormalities on T2-weighted images have been described; thus, the aim of our study was to compare the value of different MR images in the diagnosis of CJD. METHODS: One hundred fifty-seven patients with CJD underwent MR imaging examinations. Ninety-two patients were neuropathologically confirmed, and 65 were clinically classified as having CJD through the CJD Surveillance Unit (probability of 95%). There was no standardized MR imaging protocol; thus, the examinations included 143 T2-weighted, 43 proton attenuation (PD)-weighted, 84 fluid-attenuated inversion recovery (FLAIR), and 44 diffusion-weighted images (DWI). The MR images were reviewed for pathologic changes of the basal ganglia, thalamus, and cerebral cortex. RESULTS: Cortical abnormalities were present in 70 patients (45%) and were visible in 80% (35/44) of all available DWI examinations. The basal ganglia were affected in 94 patients (60%), in particular in the caudate nucleus; the most sensitive sequences were DWI (64%) and PD-weighted (63%). A thalamic involvement was more frequently diagnosed on PD-weighted images (19%) and DWI (14%) than on FLAIR or T2-weighted images. CONCLUSION: PD-weighted images and DWI showed better results in the diagnosis of signal intensity changes in the basal ganglia compared with T2-weighted or FLAIR images; however, in the diagnosis of cortical changes, DWI was clearly superior. Our data suggest that DWI is the most sensitive MR imaging technique in the diagnosis of CJD.

Because of the stochastic nature of self-amplified spontaneous emission (SASE), it is crucial to measure for single pulses the spectral characteristics of ultrashort pulses from the vacuum ultraviolet free electron laser (FLASH) at DESY, Germany. To meet this particular challenge, we have employed both photon and photoelectron spectroscopy. Each FEL pulse is composed of an intense and spectrally complex fundamental, centered at a photon energy of about 38.5 eV, with a bandwidth of 0.5% accompanied by higher harmonics, each carrying an intensity of typically 0.3 to 0.6% of that of the fundamental. The correlation between the harmonics and the fundamental is in remarkable agreement with a simple statistical model of SASE FEL radiation. (c) 2006 Optical Society of America

A stigmatic spectrometer for the 2.5–40 nm extreme-ultraviolet (EUV) region has been realized. The design consists of a grazing-incidence spherical varied-line-spaced grating with flat-field properties and of a spherical mirror mounted in the Kirkpatrick–Baez configuration that compensates for the astigmatism. The spectrum is acquired on a fluorescent screen and intensified CCD detector that can be moved along the spectral focal curve to select the spectral region to be acquired. This stigmatic design has also spectral and spatial resolution capability for extended sources. The spectral and spatial resolution of the system has been characterized by using the emission from a hollow-cathode lamp or a laser-produced plasma. At present, the instrument is installed at the vacuum–ultraviolet free-electron-laser (VUV FEL) at DESY for the spectral monitoring of the FEL beam in the 20–40 nm region.

Ziele: Die Diagnose der CJD wird an autoptisch oder bioptisch gewonnenem Hirngewebe gestellt. Die Magnetresonanztomographie spielt eine zunehmend wichtige Rolle, seit Stammganglienanomalien in T2w- und PDw- Sequenzen beschrieben wurden. Einzelberichte von der Nutzlichkeit von FLAIR oder diffusionsgewichteter MRT (DWI) wurden kurzlich veroffentlicht. Das Ziel unserer Studie war die Bestimmung der Wertigkeit verschiedener MR-tomographischer Verfahren (T2w, PDw, FLAIR, DWI) in der Diagnostik der CJD. Methode: 154 Patienten mit klinisch „wahrscheinlicher“ CJD (p>95%) wurden MR-tomographisch untersucht und retrospektiv ausgewertet. Es lagen vor: 141 T2w-, 43 PDw-, 84 FLAIR- und 44 DWI-Untersuchungen. Die Untersuchungen wurden bzgl. pathologischer Veranderungen in den Basalganglien (getrennt in Putamen und Nucl. caudatus), des Thalamus und des Cortex cerebri ausgewertet. Ergebnis: Hyperintense Signalveranderungen wurden im Putamen mit den verschiedenen MR-Techniken in folgenden Haufigkeiten gefunden: T2w 38% (54/141), PDw 58% (25/43), FLAIR 37% (31/84) und DWI 45% (20/44). Die korrespondierenden Werte fur den Nucl. caudatus waren: T2w 35% (50/141), PDw 63% (27/43), FLAIR 48% (40/84) und DWI 64% (28/44). Im Thalamus fanden sich folgende Werte: T2w 5% (7/141), PDw 19% (8/43), FLAIR 8% (7/84), DWI 14% (6/44). Im Nachweis hyperintenser Signalveranderungen im Cortex cerebri zeigten sich jedoch deutliche Unterschiede in der Empfindlichkeit der verschiedenen MR-Techniken: T2w 6% (8/141), PDw 19% (8/43), FLAIR 50% (42/84), DWI 77% (34/44). Schlussfolgerung: Bezuglich des Nachweises hyperintenser Signalveranderungen in den Stammganglien und des Thalamus wiesen die verschiedenen MR-Untersuchungstechniken keine signifikanten Unterschiede auf. FLAIR und DWI waren den anderen MR-Untersuchungstechniken im Nachweis hyperintenser Kortexveranderungen deutlich uberlegen. DWI war die sensitivste Untersuchungstechnik zum Nachweis der bisher selten beschriebenen hyperintensen kortikalen Signalveranderungen bei CJD.

We present an overview of the vacuum‐ultraviolet free electron laser (VUV FEL) user facility at DESY comprising the layout of the experimental hall, radiation transport to the experimental area, as well as photon beam diagnostics. In general, diagnostics of the FEL radiation is particularly challenging due to the laser’s unique properties such as extremely high peak powers and short pulse lengths. Yet, pulse‐resolved characterization of the photon beam is essential for most user experiments. In order to monitor important parameters like radiation pulse intensity, spectral distribution, etc. new concepts have been developed allowing efficient use of the new source.

In this paper, we describe optical feedback system of VUV Regenerative FEL Amplifier (RAFEL) at the TESLA test facility at DESY. The aim of the RAFEL experiment is to construct fully coherent, tunable VUV radiation source by means of applying narrow-band optical feedback in the VUV SASE FEL operating currently at DESY. One of the problem of the realization of the RAFEL is severe requirements for the angular stability of the optical elements (about few microradians). This problem has been solved by means of installation of active alignment system with reference laser. Another problem is alignment of optical elements separated by 65 m within complicated experimental conditions connected with aperture limitations (down to 6 mm ) . This problem has been solved in two steps. Preliminary alignment with an accuracy of about 80 μrad has been performed with laser alignment system and OTR screens used at the TTF accelerator for electron beam diagnostics. Final alignment has been performed with VUV SASE FEL radiation. Measured feedback coefficient is about 1 percent and is in agreement with the designed value.

FLASH, the Free-electron LASer in Hamburg, is a worldwide unique source for extremely bright ultra-short laser-like pulses tunable in a wide spectral range in the extreme ultraviolet and soft x-ray region (Ackermann et?al 2007 Nat. Photonics 1 336?42). To fully exploit the features of this new generation of light sources, a user facility with efficient radiation transport to the experimental area and novel online photon diagnostics capable of characterizing the unique parameters of the FLASH radiation has been built. It serves a broad user community active in many scientific fields ranging from atomic and molecular physics to plasma and solid state physics as well as chemistry and biology. A special focus is placed on the exploitation of the ultra-short FLASH pulses using pump?probe techniques. Thus, the facility is equipped with optical and THz sources synchronized to FLASH. This paper gives a detailed overview of the FLASH user facility.

A method has been developed and applied to measure the beam waist and spot size of a focused soft x-ray beam at the free-electron laser FLASH of the Deutsches Elektronen-Synchrotron in Hamburg. The method is based on a saturation effect upon atomic photoionization and represents an indestructible tool for the characterization of powerful beams of ionizing electromagnetic radiation. At the microfocus beamline BL2 at FLASH, a full width at half maximum focus diameter of (15±2)μm was determined.