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.Comment: 11 figure

Calibration Sources and Techniques for Large Format X-Ray Imagers at XFEL

In this work we compare different calibration sources and focus on their combination to optimize the calibration of large-format X-ray imagers over a wide range. This activity is carried out in the framework of the DSSC project and the primary aim is the calibration of the DSSC camera. We considered pulsed IR laser, radioactive sources, X-ray tube, electrical injection devices, X-ray synchrotron beam, low-energy protons, LED sources. The relevant features (deposited energy and pulse width) are critically summarized and calibration strategies will be discussed

Study of Systematic and Statistical Uncertainty in Offset, Noise, and Gain Determination of the DSSC Detector for the European XFEL

The DSSC (DEPFET Sensor with Signal Compression) is a new instrument with non-linear response and parallel signal processing (filtering, linear amplification, and 8-bit digitization) for all pixels. The DSSC will serve as ultra-fast megapixel imaging detector at the European XFEL (X-ray Free Electron Laser) in Schenefeld, Germany, which began science operation in September this year. The DSSC detector needs to be calibrated for each of a set of twelve predefined operation modes before being employed in scientific experiments. A crucial step in the calibration of the response of each individual detector pixel is the calibration of offset and gain. We present a study of both systematic and statistical uncertainty in the determination of offset, noise, and gain. The best possible calibration of offset and gain requires that these two quantities can be determined with an uncertainty that is less than half the finite resolution of the respective read-out ASIC calibration settings. The study is based on simulated calibration data, which were then analyzed using our calibration tools. Systematic and statistical uncertainty in offset, noise, and gain determination was quantified by comparing analysis results with the actual values employed in the simulations. A review of all results identified the most suitable calibration approaches. Their ability for providing the best possible offset and gain calibration is discussed

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 250eV and 6keV , and must provide a peak frame rate of 4.5MHz 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 512×128 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 18°C . An outstanding equivalent noise charge of 9.8 e−rms is achieved at 1.1-MHz frame rate and gain of 26.8 Analog-to-Digital Unit per keV (ADU/keV). At 4.5MHz and 3.1ADU/keV , a noise of 25.5 e−rms and a dynamic range of 26ke- are obtained. The highest dynamic range of 1.345Me- is reached at 2.25MHz and 1.6ADU/keV . These values can fulfill the specification of the DSSC projec

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 250eV and 6keV, and must provide a peak frame rate of 4.5MHz 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 512×128 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 18°C. An outstanding equivalent noise charge of 9.8 e⁻rms is achieved at 1.1-MHz frame rate and gain of 26.8 Analog-to-Digital Unit per keV (ADU/keV). At 4.5MHz and 3.1 ADU/keV, a noise of 25.5 e⁻rms and a dynamic range of 26 ke⁻ are obtained. The highest dynamic range of 1.345 Me⁻ is reached at 2.25 MHz and 1.6 ADU/keV. These values can fulfill the specification of the DSSC project

DSSC Prototype Ladder Operation and Performance Study at PETRA III / P04

The DSSC (DEPFET Sensor with Signal Compression) is a new instrument with non-linear response and with parallel signal processing (filtering, linear amplification, and 8bit digitization) for all pixels. The DSSC will serve as ultra-fast megapixel imaging detector at the European XFEL (X-ray Free Electron Laser) in Schenefeld, Germany, which began science operation in September this year. In December 2016, at the Variable Polarization XUV Beamline (P04) of PETRA III, the Synchrotron Radiation Source at DESY in Hamburg, Germany, a prototype ladder system with 128×512 pixels was operated and studied for the first time.The prototype system could be operated and read-out continuously throughout the beamtime. First studies of the performance of the prototype ladder system were performed using the collected data. For example, we measured for the first time the system gain for different coarse ASIC gain settings, and studied the dispersion of the gain in a 17×57 pixel sensor sub-matrix after using fine ASIC gain settings for gain trimming

Calibration methods for charge integrating detectors

Since the introduction of the extremely intense X-ray free electron lasers, the need for low noise, high dynamic range and potentially fast charge integrating detectors has increased significantly. Among all the problems that research and development groups have to face in the development of such detectors, their calibration represents one of the most challenging and the collaboration between the detector development and user groups is of fundamental importance. The main challenge is to develop a calibration suite that is capable to test the detector over a wide dynamic range, with a high granularity and a very high linearity, together with a certain radiation tolerance and the possibility to well define the timings and the synchronization with the detector. Practical considerations have also to be made like the possibility to calibrate the detector in a reasonable time, the availability of the calibration source at the experimental place and so on. Such a calibration test suite is often not represented by a single source but by several sources that can cover different parts of the dynamic range and that need to be cross calibrated to have a final calibration curve. In this respect an essential part of the calibration is also to develop a mathematical model that allows calibrating the entire dynamic range, taking into account features that are calibration source and/or detector specific. The aim of this contribution is to compare the calibration for the AGIPD detector using several calibration sources such as internal current source, backside pulsing, IR pulsed laser, LED light and mono-energetic protons. The mathematical procedure used to cali-brate the different sources will be discussed in great detail showing how to take into account a few shortcomings (like pixel coupling) that are common for many charge integrating detectors. This work has been carried out in the frame of the AGIPD project for the European X-ray Free Electron Laser

DSSC Prototype Ladder Operation and Performance Study at PETRA III / P04

The DSSC (DEPFET Sensor with Signal Compression) is a new instrument with non-linear response and with parallel signal processing (filtering, linear amplification, and 8bit digitization) for all pixels. The DSSC will serve as ultra-fast megapixel imaging detector at the European XFEL (X-ray Free Electron Laser) in Schenefeld, Germany, which began science operation in September this year. In December 2016, at the Variable Polarization XUV Beamline (P04) of PETRA III, the Synchrotron Radiation Source at DESY in Hamburg, Germany, a prototype ladder system with 128×512 pixels was operated and studied for the first time.The prototype system could be operated and read-out continuously throughout the beamtime. First studies of the performance of the prototype ladder system were performed using the collected data. For example, we measured for the first time the system gain for different coarse ASIC gain settings, and studied the dispersion of the gain in a 17×57 pixel sensor sub-matrix after using fine ASIC gain settings for gain trimming