A 64k pixel CMOS-DEPFET module for the soft X-rays DSSC imager operating at MHz-frame rates

: The 64k pixel DEPFET module is the key sensitive component of the DEPFET Sensor with Signal Compression (DSSC), a large area 2D hybrid detector for capturing and measuring soft X-rays at the European XFEL. The final 1-megapixel camera has to detect photons with energies between [Formula: see text] and [Formula: see text], and must provide a peak frame rate of [Formula: see text] to cope with the unique bunch structure of the European XFEL. This work summarizes the functionalities and properties of the first modules assembled with full-format CMOS-DEPFET arrays, featuring [Formula: see text] hexagonally-shaped pixels with a side length of 136 μm. The pixel sensors utilize the DEPFET technology to realize an extremely low input capacitance for excellent energy resolution and, at the same time, an intrinsic capability of signal compression without any gain switching. Each pixel of the readout ASIC includes a DEPFET-bias current cancellation circuitry, a trapezoidal-shaping filter, a 9-bit ADC and a 800-word long digital memory. The trimming, calibration and final characterization were performed in a laboratory test-bench at DESY. All detector features are assessed at [Formula: see text]. An outstanding equivalent noise charge of [Formula: see text]e-rms is achieved at 1.1-MHz frame rate and gain of 26.8 Analog-to-Digital Unit per keV ([Formula: see text]). At [Formula: see text] and [Formula: see text], a noise of [Formula: see text] e-rms and a dynamic range of [Formula: see text] are obtained. The highest dynamic range of [Formula: see text] is reached at [Formula: see text] and [Formula: see text]. These values can fulfill the specification of the DSSC project

The interplay of local electron correlations and ultrafast spin dynamics in fcc Ni

The complex electronic structure of metallic ferromagnets is determined by a balance between exchange interaction, electron hopping leading to band formation, and local Coulomb repulsion. The interplay between the respective terms of the Hamiltonian is of fundamental interest, since it produces most, if not all, of the exotic phenomena observed in the solid state. By combining high energy and temporal resolution in femtosecond time-resolved X-ray absorption spectroscopy with ab initio time-dependent density functional theory we analyze the electronic structure in fcc Ni on the time scale of these interactions in a pump-probe experiment. We distinguish transient broadening and energy shifts in the absorption spectra, which we demonstrate to be caused by electron repopulation and correlation-induced modifications of the electronic structure, respectively. Importantly, the theoretical description of this experimental result hence requires to take the local Coulomb interaction into account, revealing a temporal interplay between band formation, exchange interaction, and Coulomb repulsion

Photon shot-noise limited transient absorption soft X-ray spectroscopy at the European XFEL

Femtosecond transient soft X-ray Absorption Spectroscopy (XAS) is a very promising technique that can be employed at X-ray Free Electron Lasers (FELs) to investigate out-of-equilibrium dynamics for material and energy research. Here we present a dedicated setup for soft X-rays available at the Spectroscopy & Coherent Scattering (SCS) instrument at the European X-ray Free Electron Laser (EuXFEL). It consists of a beam-splitting off-axis zone plate (BOZ) used in transmission to create three copies of the incoming beam, which are used to measure the transmitted intensity through the excited and unexcited sample, as well as to monitor the incoming intensity. Since these three intensity signals are detected shot-by-shot and simultaneously, this setup allows normalized shot-by-shot analysis of the transmission. For photon detection, the DSSC imaging detector, which is capable of recording up to 800 images at 4.5 MHz frame rate during the FEL burst, is employed and allows approaching the photon shot-noise limit. We review the setup and its capabilities, as well as the online and offline analysis tools provided to users

Megahertz-rate ultrafast X-ray scattering and holographic imaging at the European XFEL

The advent of X-ray free-electron lasers (XFELs) has revolutionized fundamental science, from atomic to condensed matter physics, from chemistry to biology, giving researchers access to X-rays with unprecedented brightness, coherence and pulse duration. All XFEL facilities built until recently provided X-ray pulses at a relatively low repetition rate, with limited data statistics. Here, results from the first megahertz-repetition-rate X-ray scattering experiments at the Spectroscopy and Coherent Scattering (SCS) instrument of the European XFEL are presented. The experimental capabilities that the SCS instrument offers, resulting from the operation at megahertz repetition rates and the availability of the novel DSSC 2D imaging detector, are illustrated. Time-resolved magnetic X-ray scattering and holographic imaging experiments in solid state samples were chosen as representative, providing an ideal test-bed for operation at megahertz rates. Our results are relevant and applicable to any other non-destructive XFEL experiments in the soft X-ray range

Observation of fluctuation-mediated picosecond nucleation of a topological phase

peer reviewedTopological states of matter exhibit fascinating physics combined with an intrinsic stability. A key challenge is the fast creation of topological phases, which requires massive reorientation of charge or spin degrees of freedom. Here we report the picosecond emergence of an extended topological phase that comprises many magnetic skyrmions. The nucleation of this phase, followed in real time via single-shot soft X-ray scattering after infrared laser excitation, is mediated by a transient topological fluctuation state. This state is enabled by the presence of a time-reversal symmetry-breaking perpendicular magnetic field and exists for less than 300 ps. Atomistic simulations indicate that the fluctuation state largely reduces the topological energy barrier and thereby enables the observed rapid and homogeneous nucleation of the skyrmion phase. These observations provide fundamental insights into the nature of topological phase transitions, and suggest a path towards ultrafast topological switching in a wide variety of materials through intermediate fluctuating states. © 2020, The Author(s), under exclusive licence to Springer Nature Limited.Leibniz Association Grant no. K162/2018 (OptiSPIN

Study of PMOS front-end solution with signal compression for XFEL MiniSDD X-ray detectors

In this work we present the study and the experimental results on two different front-end stages for the MmiSDD pixel sensors of the DSSC detector for photon science applications at the European XFEL GmbH in Hamburg. The detector must be able to cope with an image frame rate up to 4.5 MHz and must achieve a dynamic range up to 104photons/pixel/pulse with a photon energy of 1 keV. In order to achieve this high dynamic range and single photon sensitivity at the same time, the front-end must provide a non-linear amplification. The non-linear response is obtained with a simple circuit that pushes the input PMOSFET into triode region as the input signal increases. Since the readout ASIC has more than 4000 channels operating in parallel, particular care was devoted to the homogeneity and the robustness of the implemented solution, especially with respect to power supply rejection ratio and the cross talk among channels

An open-loop front-end stage with signal compression capability and improved PSRR for mini-SDD pixel detectors

In this work we present the design and the experimental characterization of a front-end stage for X-ray pixel sensors. Our study was carried out in the framework of the DSSC detector development for the European XFEL (X-ray Free Electron Laser). The DSSC detector is going to be used in photon science applications at the European XFEL GmbH in Hamburg, Germany, and must be able to cope with an image frame rate up to 4.5 MHz. Moreover, the single photon sensitivity and a dynamic range up to 104 photons/pixel/pulse, with a photon energy of 1 keV, is required at the same time. Therefore, to achieve these requirement the front-end must provide a non-linear amplification. The non-linear response is obtained with a simple circuit that pushes the input PMOSFET into triode region as the input signal increases. However, since the readout ASIC has more than 4000 channels operating in parallel, particular care was devoted to the robustness of the implemented solution, especially with respect to power supply rejection ratio and crosstalk among channels

Study of PMOS Front-End Solution with Signal Compression for XFEL MiniSDD X-Ray Detectors

In this work we present the study and the experimental results on two different front-end stages for the MiniSDD pixel sensors of the DSSC detector for photon science applications at the European XFEL GmbH in Hamburg. The detector must be able to cope with an image frame rate up to 4.5 MHz and must achieve a dynamic range up to 104 photons/pixel/pulse with a photon energy of 1 keV. In order to achieve this high dynamic range and single photon sensitivity at the same time, the front-end must provide a non-linear amplification. The non-linear response is obtained with a simple circuit that pushes the input PMOSFET into triode region as the input signal increases. Since the readout ASIC has more than 4000 channels operating in parallel, particular care was devoted to the homogeneity and the robustness of the implemented solution, especially with respect to power supply rejection ratio and the cross talk among channels

Charge Sensitive Amplifier with Offset-Compensated V-to-I Converter for the Mini-SDD-Based DSSC Detector

In this article, we present the study and the experimental results of a charge sensitive amplifier (CSA) for the mini-silicon drift detector (SDD) pixel sensors of the DEPleted Field-Effect Transistor (DEPFET) sensor with signal compression (DSSC) detector for photon science applications at the European X-ray free electron laser (XFEL) GmbH in Hamburg area. The DSSC detector must be able to cope with an image frame rate up to 4.5 MHz and with a dynamic range up to 104 photons/pixel/pulse for a photon energy of 1 keV. These goals will be pursued with the adoption of the DEPFET detector strategy. For the first camera prototype, a simpler solution based on a mini-SDD array read out by a conventional CSA has been adopted. We present here the CSA solution with a very simple V-to-I converter stage, which allows the self-canceling of the offset current flowing between the CSA and the filter, without the need of an intermediate stage. The CSA is compatible with the same application-specified integrated circuit (ASIC) architecture and readout chain already designed for the DEPFET detector. We present two versions of the CSA: one with a linear response and another with a nonlinear output characteristic. The nonlinear version provides increased input dynamic range preserving single-photon sensitivity. The experimental measurements have demonstrated the functionality of the proposed self-canceling solution and good noise performance with an equivalent noise charge (ENC) of 65 e- rms at the 4.5-MHz frame rate and a linearity error lower than 0.25% of the complete channel. In addition, the functionality of the nonlinear version (signal compression version) of the CSA has been demonstrated, without penalty in noise performance in the linear region of the CSA response