Search

We present the first lasing results of SwissFEL, a hard X-ray free-electron laser (FEL) that recently came into operation at the Paul Scherrer Institute in Switzerland. SwissFEL is a very stable, compact and cost-effective X-ray FEL facility driven by a low-energy and ultra-low-emittance electron beam travelling through short-period undulators. It delivers stable hard X-ray FEL radiation at 1-A wavelength with pulse energies of more than 500 μJ, pulse durations of ~30 fs (root mean square) and spectral bandwidth below the per-mil level. Using special configurations, we have produced pulses shorter than 1 fs and, in a different set-up, broadband radiation with an unprecedented bandwidth of ~2%. The extremely small emittance demonstrated at SwissFEL paves the way for even more compact and affordable hard X-ray FELs, potentially boosting the number of facilities worldwide and thereby expanding the population of the scientific community that has access to X-ray FEL radiation. The first lasing results at SwissFEL, an X-ray free-electron laser, are presented, highlighting the facility’s unique capabilities. A general comparison to other major facilities is also provided.

Use of the charge-integrating JUNGFRAU detector for fluorescence detection is investigated, and its applications in macromolecular crystallography at synchrotron and X-ray free-electron laser sources are demonstrated., Detection of heavy elements, such as metals, in macromolecular crystallography (MX) samples by X-ray fluorescence is a function traditionally covered at synchrotron MX beamlines by silicon drift detectors, which cannot be used at X-ray free-electron lasers because of the very short duration of the X-ray pulses. Here it is shown that the hybrid pixel charge-integrating detector JUNGFRAU can fulfill this function when operating in a low-flux regime. The feasibility of precise position determination of micrometre-sized metal marks is also demonstrated, to be used as fiducials for offline prelocation in serial crystallography experiments, based on the specific fluorescence signal measured with JUNGFRAU, both at the synchrotron and at SwissFEL. Finally, the measurement of elemental absorption edges at a synchrotron beamline using JUNGFRAU is also demonstrated.

Synchrotrons and modern FEL light sources operate with bunch repetition rates in the MHz range. The profile of the electron beam inside the accelerator can be characterized with indirect experimental techniques where linear array detectors are employed to measure the emitted synchrotron radiation or the spectrum of a near-IR laser. To improve the performance of modern beam diagnostics we have developed KALYPSO, a detector system operating with a continuous frame rate of up to 2.7 MHz. To facilitate the integration in different experiments, a modular architecture has been adopted. Different semiconductor micro-strip sensors can be connected to front-end ASICs to optimize the quantum efficiency at different photon energies, ranging from visible light up to near-IR. The front-end electronics are integrated within an heterogeneous DAQ consisting of FPGAs and GPUs, which allows scientists to implement real-time data processing algorithms. The current version of the detector is in operation at the KARA synchrotron light source and at the European XFEL. In this contribution we present the detector architecture, the performance results and the on-going technical developments.

International audience; The Bernina instrument at the SwissFEL Aramis hard X-ray free-electron laser is designed for studying ultrafast phenomena in condensed matter and material science. Ultrashort pulses from an optical laser system covering a large wavelength range can be used to generate specific non-equilibrium states, whose subsequent temporal evolution can be probed by selective X-ray scattering techniques in the range 2–12 keV. For that purpose, the X-ray beamline is equipped with optical elements which tailor the X-ray beam size and energy, as well as with pulse-to-pulse diagnostics that monitor the X-ray pulse intensity, position, as well as its spectral and temporal properties. The experiments can be performed using multiple interchangeable endstations differing in specialization, diffractometer and X-ray analyser configuration and load capacity for specialized sample environment. After testing the instrument in a series of pilot experiments in 2018, regular user operation begins in 2019.

Gotthard-II is a charge-integrating microstrip detector developed for experiments and diagnostics at free-electron lasers using hard X-rays of 5 keV - 20 keV. Thanks to its excellent single photon sensitivity, large dynamic range as well as high frame rate of 4.5 MHz in burst mode, its potential scientific applications include X-ray absorption/emission spectroscopy, hard X-ray high resolution single-shot spectrometry (HiREX), beam diagnostics, as well as veto signal generation for pixel detectors. The Gotthard-II ASIC has been designed and fabricated using UMC-110 nm technology. The final ASIC design and performance in terms of noise, linearity, dynamic range, coupling between channels and speed will be discussed in the paper. In addition, a first measurement of an X-ray absorption spectrum of a standard copper sample has been done. The performance of the Gotthard-II in an experiment using energy dispersive X-rays has been demonstrated., 25 pages, 16 figures

Optical-domain Transient Grating (TG) spectroscopy is a versatile background-free four-wave-mixing technique used to probe vibrational, magnetic and electronic degrees of freedom in the time domain. The newly developed coherent X-ray Free Electron Laser sources allow its extension to the X-ray regime. Xrays offer multiple advantages for TG: their large penetration depth allows probing the bulk properties of materials, their element-specificity can address core-excited states, and their short wavelengths create excitation gratings with unprecedented momentum transfer and spatial resolution. We demonstrate for the first time TG excitation in the hard X-ray range at 7.1 keV. In Bismuth Germanate (BGO), the nonresonant TG excitation generates coherent optical phonons detected as a function of time by diffraction of an optical probe pulse. This experiment demonstrates the ability to probe bulk properties of materials and paves the way for ultrafast coherent four-wave-mixing techniques using X-ray probes and involving nanoscale TG spatial periods., Comment: 11 pages, 4 figures

Chromium compensated GaAs or GaAs:Cr sensors provided by the Tomsk State University (Russia) were characterized using the low noise, charge integrating readout chip JUNGFRAU with a pixel pitch of 75 × 75 µm2 regarding its application as an X-ray detector at synchrotrons sources or FELs. Sensor properties such as dark current, resistivity, noise performance, spectral resolution capability and charge transport properties were measured and compared with results from a previous batch of GaAs:Cr sensors which were produced from wafers obtained from a different supplier. The properties of the sample from the later batch of sensors from 2017 show a resistivity of 1.69 × 109 Ω/cm, which is 47% higher compared to the previous batch from 2016. Moreover, its noise performance is 14% lower with a value of (101.65 ± 0.04) e- ENC and the resolution of a monochromatic 60 keV photo peak is significantly improved by 38% to a FWHM of 4.3%. Likely, this is due to improvements in charge collection, lower noise, and more homogeneous effective pixel size. In a previous work, a hole lifetime of 1.4 ns for GaAs:Cr sensors was determined for the sensors of the 2016 sensor batch, explaining the so-called “crater effect” which describes the occurrence of negative signals in the pixels around a pixel with a photon hit due to the missing hole contribution to the overall signal causing an incomplete signal induction. In this publication, the “crater effect” is further elaborated by measuring GaAs:Cr sensors using the sensors from 2017. The hole lifetime of these sensors was 2.5 ns. A focused photon beam was used to illuminate well defined positions along the pixels in order to corroborate the findings from the previous work and to further characterize the consequences of the “crater effect” on the detector operation.

Thanks to the remarkable developments of ultrafast science, one of today's challenges is to modify material state by controlling with a light pulse the coherent motions that connect two different phases. Here we show how strain waves, launched by electronic and structural precursor phenomena, determine a macroscopic transformation pathway for the semiconducting-to-metal transition with large volume change in bistable Ti$_3$O$_5$ nanocrystals. Femtosecond powder X-ray diffraction allowed us to quantify the structural deformations associated with the photoinduced phase transition on relevant time scales. We monitored the early intra-cell distortions around absorbing metal dimers, but also long range crystalline deformations dynamically governed by acoustic waves launched at the laser-exposed Ti$_3$O$_5$ surface. We rationalize these observations with a simplified elastic model, demonstrating that a macroscopic transformation occurs concomitantly with the propagating acoustic wavefront on the picosecond timescale, several decades earlier than the subsequent thermal processes governed by heat diffusion., 30 pages (including supplementary text), 5 main figures, 9 supplementary figures; corrected author list

JUNGFRAU is the pixel detector developed at PSI for SwissFEL [1]. Although the detector development was driven by the SwissFEL requirements, it was soon realized that such a detector could also be ...

The accuracy of X-ray diffraction data is directly related to how the X-ray detector records photons. Here we describe the application of a direct-detection charge-integrating pixel-array detector (JUNGFRAU) in macromolecular crystallography (MX). JUNGFRAU features a uniform response on the subpixel level, linear behavior toward high photon rates, and low-noise performance across the whole dynamic range. We demonstrate that these features allow accurate MX data to be recorded at unprecedented speed. We also demonstrate improvements over previous-generation detectors in terms of data quality, using native single-wavelength anomalous diffraction (SAD) phasing, for thaumatin, lysozyme, and aminopeptidase N. Our results suggest that the JUNGFRAU detector will substantially improve the performance of synchrotron MX beamlines and equip them for future synchrotron light sources. published

MYTHEN 3 is a new single-photon-counting readout chip being developed by the SLS detector group in 110 nm UMC technology. It will equip a 60 k-channel, 50 μ m pitch microstrip detector optimized for powder diffraction experiments. Every readout channel features an amplifier and a shaper with variable gain and shaping time. The shaper output is fed to three independent discriminators, each one having a dedicated threshold, trim bit set and enable signal. The outputs of the three discriminators are processed by the counting logic section which, according to the mode of operation selected, generates the hits for the three following 24-bit counters. Several operation modes are foreseen: dual polarity, energy-windowing, count rate improvement, charge sharing suppression and pump with multiple probe time slots. The first 64-channel prototype has been tested in the lab, with fluorescence X-rays and with a synchrotron beam to characterize its noise and count rate capability. Based on the results obtained from the first chip a second 64-channel prototype has been developed and sent to production. The architecture of the chip and characterization results of the first chip will be presented.

In this paper, we present a data workflow developed to operate the adJUstiNg Gain detector FoR the Aramis User station (JUNGFRAU) adaptive gain charge integrating pixel-array detectors at macromolecular crystallography beamlines. We summarize current achievements for operating at 9 GB/s data-rate a JUNGFRAU with 4 Mpixel at 1.1 kHz frame-rate and preparations to operate at 46 GB/s data-rate a JUNGFRAU with 10 Mpixel at 2.2 kHz in the future. In this context, we highlight the challenges for computer architecture and how these challenges can be addressed with innovative hardware including IBM POWER9 servers and field-programmable gate arrays. We discuss also data science challenges, showing the effect of rounding and lossy compression schemes on the MX JUNGFRAU detector images., Structural Dynamics, 7 (1), ISSN:2329-7778

OLED technology beyond small or expensive devices requires light-emitters, luminophores, based on earth-abundant elements. Understanding and experimental verification of charge transfer in luminophores are needed for this development. An organometallic multicore Cu complex comprising Cu–C and Cu–P bonds represents an underexplored type of luminophore. To investigate the charge transfer and structural rearrangements in this material, we apply complementary pump-probe X-ray techniques: absorption, emission, and scattering including pump-probe measurements at the X-ray free-electron laser SwissFEL. We find that the excitation leads to charge movement from C- and P- coordinated Cu sites and from the phosphorus atoms to phenyl rings; the Cu core slightly rearranges with 0.05 Å increase of the shortest Cu–Cu distance. The use of a Cu cluster bonded to the ligands through C and P atoms is an efficient way to keep structural rigidity of luminophores. Obtained data can be used to verify computational methods for the development of luminophores., Nature Communications, 11 (1), ISSN:2041-1723

The AGIPD (adaptive gain integrating pixel detector) detector is a high frame rate (4.5 MHz) and high dynamic range (up to 10 4 ·12.4 keV photons) detector with single photon resolution (down to 4 keV taking 5 σ as limit and lowest noise settings) developed for the European XFEL (XFEL.EU). This work is focused on the characterization of AGIPD1.0, which is the first full scale version of the chip. The chip is 64×64 pixels and each pixel has a size of 200×200 μm 2 . Each pixel can store up to 352 images at a rate of 4.5 MHz (corresponding to 220 ns). A detailed characterization of the AGIPD1.0 chip has been performed in order to assess the main performance of the ASIC in terms of gain, noise, speed and dynamic range. From the measurements presented in this paper a good uniformity of the gain, a noise around 320 e − (rms) in standard mode and around 240 e − (rms) in high gain mode has been measured. Furthermore a detailed discussion about the non-linear behavior after the gain switching is presented with both experimental results and simulations.

MÖNCH is a 25 µm-pitch charge-integrating detector aimed at exploring the limits of current hybrid silicon detector technology. The small pixel size makes it ideal for high-resolution imaging. With an electronic noise of about 110 eV r.m.s., it opens new perspectives for many synchrotron applications where currently the detector is the limiting factor, e.g. inelastic X-ray scattering, Laue diffraction and soft X-ray or high-resolution color imaging. Due to the small pixel pitch, the charge cloud generated by absorbed X-rays is shared between neighboring pixels for most of the photons. Therefore, at low photon fluxes, interpolation algorithms can be applied to determine the absorption position of each photon with a resolution of the order of 1 µm. In this work, the characterization results of one of the MÖNCH prototypes are presented under low-flux conditions. A custom interpolation algorithm is described and applied to the data to obtain high-resolution images. Images obtained in grating interferometry experiments without the use of the absorption grating G2 are shown and discussed. Perspectives for the future developments of the MÖNCH detector are also presented., Journal of Synchrotron Radiation, 23 (6), ISSN:0909-0495, ISSN:1600-5775

Measurements of mixed radiation fields are challenging, partly due to the high demands on dynamic range and large energy depositions from for example heavy ions. We show that the JUNGFRAU detector developed for photon science at free electron lasers is capable of accurately measuring the energy deposition of four different ion species from He 230 MeV/A with an Linear Energy Transfer (LET) of 3 keV/μm to Fe 290 MeV/A with an LET of 440 keV/μm , even at 0o polar angle with a 320μm thick silicon sensor.

The evolution of the bismuth crystal structure upon excitation of its A$_{1g}$ phonon has been intensely studied with short pulse optical lasers. Here we present the first-time observation of a hard x-ray induced ultrafast phase transition in a bismuth single crystal, at high intensities (~$10^{14}$ W/cm$^2$). The lattice evolution was followed using a recently demonstrated x-ray single-shot probing setup. The time evolution of the (111) Bragg peak intensity showed strong dependence on the excitation fluence. After exposure to a sufficiently intense x-ray pulse, the peak intensity dropped to zero within 300fs, i.e. faster than one oscillation period of the A1g mode at room temperature. Our analysis indicates a nonthermal origin of a lattice disordering process, and excludes interpretations based on electron-ion equilibration process, or on thermodynamic heating process leading to a plasma formation., Comment: Main text 10 pages, 3 figures. Appendix 3 pages, 2 figures

Recent advances in segmented low-gain avalanche detectors (LGADs) make them promising for the position-sensitive detection of low-energy X-ray photons thanks to their internal gain. LGAD microstrip sensors fabricated by Fondazione Bruno Kessler have been investigated using X-rays with both charge-integrating and single-photon-counting readout chips developed at the Paul Scherrer Institut. In this work it is shown that the charge multiplication occurring in the sensor allows the detection of X-rays with improved signal-to-noise ratio in comparison with standard silicon sensors. The application in the tender X-ray energy range is demonstrated by the detection of the sulfur K α and K β lines (2.3 and 2.46 keV) in an energy-dispersive fluorescence spectrometer at the Swiss Light Source. Although further improvements in the segmentation and in the quantum efficiency at low energy are still necessary, this work paves the way for the development of single-photon-counting detectors in the soft X-ray energy range.

Ultrafast Imaging and Tracking Instrumentation, Methods and Applications Forum 2018, ULITIMA 2018, Argonne, IL, USA, 11 Sep 2018 - 14 Sep 2018; Nuclear instruments & methods in physics research / A Accelerators, spectrometers, detectors and associated equipment Section A 942, 162324 - (2019). doi:10.1016/j.nima.2019.06.065, The European XFEL is an extremely brilliant Free Electron Laser Source with a very demanding pulse structure: trains of 2700 X-Ray pulses are repeated at 10 Hz. The pulses inside the train are spaced by 220 ns and each one contains up to $10^{12}$ photons of 12.4 keV, while being $\rm \leq 100$ fs in length.AGIPD, the Adaptive Gain Integrating Pixel Detector, is a hybrid pixel detector developed by DESY, PSI, and the Universities of Bonn and Hamburg to cope with these properties. It is a fast, low noise integrating detector, with single photon sensitivity (for $E_{\gamma} \gtrapprox 6$ keV) and a large dynamic range, up to $10^4$ photons at 12.4 keV. This is achieved with a charge sensitive amplifier with 3 adaptively selected gains per pixel. 352 images can be recorded at up to 6.5 MHz and stored in the in-pixel analogue memory and read out between pulse trains. The core component of this detector is the AGIPD ASIC, which consists of $64 \times 64$ pixels of 200 µm $\times$ 200 µm. Control of the ASIC's image acquisition and analogue readout is via a command based interface. FPGA based electronic boards, controlling ASIC operation, image digitisation and 10 GE data transmission interface AGIPD detectors to DAQ and control systems. An AGIPD 1 Mpixel detector has been installed at the SPB experimental station in August 2017, while a second one is currently commissioned for the MID endstation. A larger (4 Mpixel) AGIPD detector and one to employ Hi-Z sensor material to efficiently register photons up to $E_{\gamma} \approx $ 25 keV are currently under construction., Published by North-Holland Publ. Co., Amsterdam

Chromium compensated GaAs sensors have been characterized using the charge-integrating readout chip JUNGFRAU. Due to its low noise performance and 75 × 75 μm2 pixel size, JUNGFRAU enables a precise measurement of the charge (of either polarity) with a high spatial resolution. Several sensor parameters like dark current, noise and spectral performance as well as the charge transport properties of the electrons have been determined. The short lifetime of holes in GaAs:Cr gives rise to an effect where pixels adjacent to a pixel with a photon hit show a strong negative signal when being absorbed close to the readout electrode. This so-called `crater effect' has been simulated and allows an estimation of the hole lifetime in GaAs:Cr.

This paper presents a study of the noise behavior of MOSFET devices belonging to a 110-nm CMOS technology in view of applications to the design of low-noise, low-power analog circuits in X-ray detection at free electron lasers (FELs) and the next generation of synchrotrons. The goal of this paper is to provide a valuable and cost-effective option, with respect to more scaled and expensive technology nodes, to designers of the detection systems of FELs and next-generation synchrotron sources. The white component of the noise voltage spectrum and the 1/ $f$ noise contribution is experimentally characterized by noise measurements in a wide frequency range. Data extracted from the characterization have been studied as a function of the bias condition and the gate dimensions (length and width). A comparison of the main parameters with less and more scaled CMOS generations is also provided.

International audience; High-Z sensors are increasingly used to overcome the poor efficiency of Si sensors above 15 keV, and further extend the energy range of synchrotron and FEL experiments. Detector-grade GaAs sensors of 500 μm thickness offer 98% absorption efficiency at 30 keV and 50% at 50 keV . In this work we assess the usability of GaAs sensors in combination with the MYTHEN photon-counting microstrip readout chip developed at PSI. Different strip length and pitch are compared, and the detector performance is evaluated in regard of the sensor material properties. Despite increased leakage current and noise, photon-counting strips mounted with GaAs sensors can be used with photons of energy as low as 5 keV, and exhibit excellent linearity with energy. The charge sharing is doubled as compared to silicon strips, due to the high diffusion coefficient of electrons in GaAs.

The SLS detectors group has a longstanding history in the development of hybrid X-ray detectors for synchrotrons [1]. Hybrid detectors consist of a sensor (usually silicon) absorbing the photons and front-end electronics transforming the charge into a measurable signal. The two parts are distinct and can therefore be optimized separately, depending on the application. The group has the know-how to design sensors and Read-Out Chips (ROC) in-house, assemble the detectors with a high yield for a large number of channels (both wire- and bump-bonding), and develop data acquisition systems and software. The detectors must provide high-quality data and be reliable for the daily user operation at the beamlines. They are normally developed to target specific applications, and particular effort is put into the integration of the systems at the beamlines and on their reliability. The detector group works in close connection with the beamline scientists of the SLS as early as the development phase and then later to t...

AGIPD, the Adaptive Gain Integrating Pixel Detector, is a hybrid detector with a frame rate of 4.5 M H z , a dynamic range up to 1 0 4 ⋅ 12.4 k e V photons, as well as single photon resolution, developed for the European XFEL (Eu.XFEL). The final 1 Mpixel detector system consists of 16 tiled modules each one with 16 readout chips. The single ASIC is 64 x 64 pixels, each with a size of 200 x 200 μ m 2 . Each pixel can store up to 352 images. This work is focused on the characterization of AGIPD1.1, the second version of the full scale ASIC, and the improvements with respect to AGIPD1.0. From the measurements presented in this paper we show that the flaws observed in AGIPD1.0 (i.e. ghosting, crosstalk, slow readout speed) have been fixed in AGIPD1.1. In addition the main performance parameters such as noise, dynamic range and so on were measured for the new version of the ASIC and will be summarized.