Lothar Strueder

Toward unsupervised single-shot diffractive imaging of heterogeneous particles using X-ray free-electron lasers

Single shot diffraction imaging experiments via X-ray free-electron lasers can generate as many as hundreds of thousands of diffraction patterns of scattering objects. Recovering the real space contrast of a scattering object from these patterns currently requires a reconstruction process with user guidance in a number of steps, introducing severe bottlenecks in data processing. We present a series of measures that replace user guidance with algorithms that reconstruct contrasts in an unsupervised fashion. We demonstrate the feasibility of automating the reconstruction process by generating hundreds of contrasts obtained from soot particle diffraction experiments.

Effect of low-energy protons on the performance of the EPIC pn-CCD detector on XMM-Newton

After the launch of Chandra, it was realized that low energy protons (below approximately 300 keV) are funnelled by grazing incident mirrors onto the focal plane detectors. Front illuminated CCD detectors are very sensitive to soft protons causing radiation damage in their electrode structures and transfer channels. The back-illuminated 280 micrometer thick fully depleted pn-CCD of the European Photon Imaging Camera (EPIC) on board the X-ray Multi Mirror mission (XMM) is by far less sensitive to low energy proton radiation. Commanding the camera in a special low gain mode, even allows to directly measure proton spectra and event patterns up to 300 keV per pixel. At the 3 MV Van-de-Graaff accelerator of the Institute for Physics in Tubingen we have irradiated and tested a 3 cm2 flight-like pn-CCD with protons from 1 to 300 keV up to a fluence of 1.4 (DOT) 109 protons/cm2. This is about a factor of 1000 above the expected solar proton fluence for a 10 year XMM-Newton mission under nominal operational conditions. In this paper we given an overview of the proton irradiation experiment, discuss the performance of the detector after proton irradiation and finally present proton spectra directly measured with the pn-CCD on board XMM-Newton during solar flares. In addition, we briefly describe the precautionary measures taken to minimize the proton radiation dose of the EPIC CCD detectors in orbit.

CAMEX readout ASICs for pnCCDs

For the readout of pnCCD we developed a series of CAMEX ASICs since the early 90’s. With the advent of DEPFET PIXEL detectors the existing CAMEX readout chip was adopted for these new detectors. The actual generation of CAMEX readout chips is fabricated in a standard 5V CMOS technology with JFET option at the Fraunhofer IMS in Duisburg, Germany. To qualify the new CAMEX readout ASICs we performed several measurements including weighting function measurements, multiplexer performance and linearity as well as performance figures of the integrated bias DACs. Performance values together with the pnCCD will be shown. Further tests will also reveal the radiation performance of the ASIC. The main application of these CAMEX chips is the X-ray astronomy project eROSITA (extended Roentgen Survey with an Imaging Telescope Array). This X-ray telescope will be accommodated aboard the new Spectrum Roentgen Gamma satellite. It consists of seven parallel oriented mirror modules (Wolter-I optics) each having its own pnCCD camera in the focus. The pnCCD detector consists of 384×384 imaging pixels with 75μm size plus a frame store area. The satellite launch is planned for the year 2011.The parallel architecture of the pnCCD and CAMEX allows lownoise readout of a full 384 × 384 pixel image within ≪8 ms. Full size prototypes of the detector system are currently under test. Another application are detectors for the evolving X-ray free electron lasers, a new generation of synchrotron light sources. X-ray FEL facilities provide pulses of coherent X-ray light of high brilliance in the energy range of below 0.3 keV up to 24 keV. New prototype pnCCDs for these applications have a size of 512x1024 pixels and are readout with 8 CAMEX chips operating in parallel to archive a frame rate of up to 200Hz.

Multichannel silicon drift detectors for x-ray spectroscopy

Silicon Drift Detectors (SDDs) with integrated readout transistor combine a large sensitive area with a small value of the output capacitance and are therefore well suited for high resolution, high count rate X-ray spectroscopy. The low leakage current level obtained by the elaborated process technology makes it possible to operate them at room temperature or with moderate cooling. The monolithic combination of a number of SDDs to a Multichannel Drift Detector solves the limitation in size of the single device and allows the realization of new physics experiments and systems. The description of the device principle is followed by the introduction of the Multichannel Drift Detector concept. Layout, performance, and examples of current and future applications are given.

Sensing the wavefront of x-ray free-electron lasers using aerosol spheres

Characterizing intense, focused x-ray free electron laser (FEL) pulses is crucial for their use in diffractive imaging. We describe how the distribution of average phase tilts and intensities on hard x-ray pulses with peak intensities of 10(21) W/m(2) can be retrieved from an ensemble of diffraction patterns produced by 70 nm-radius polystyrene spheres, in a manner that mimics wavefront sensors. Besides showing that an adaptive geometric correction may be necessary for diffraction data from randomly injected sample sources, our paper demonstrates the possibility of collecting statistics on structured pulses using only the diffraction patterns they generate and highlights the imperative to study its impact on single-particle diffractive imaging.

Room-temperature x- and gamma-ray spectroscopy with silicon drift detectors

Silicon Drift Detectors (SDDs) with integrated readout transistors combine a large sensitive area with a small total readnode capacitance and are therefore well suited for high resolution, high count rate X-ray spectroscopy. The low leakage current level obtained by elaborated process technology makes it possible to operate them at room temperature or with moderate thermo-electric cooling. The monolithic combination of several SDDs to a multichannel drift detector solves the limited of size and allows for the realization of new physics experiments and systems. Up to 3 cm2 large SDDs for spectroscopic applications were fabricated and tested. Position sensitive X-ray systems are introduced. The description of the device principle is followed by the introduction of the multichannel drift detector concept. Layout, performance and examples of current and future applications are presented.

Development and Characterization of New 256

DEPFET detectors are silicon (Si) active pixel sensors designed and manufactured in the Max-Planck-Institut semiconductor lab. Their high spatial resolution and high energy resolution in X-rays make them attractive for particle tracking in colliders and for X-ray astronomy. This technology is foreseen for the Wide Field Imager of the International X-ray Observatory currently in study with ESA, NASA, and JAXA. New DEPFET matrixes with 256 × 256 pixels of 75-μm pitch have been produced, mounted on ceramic boards with dedicated front-end electronics and integrated in a new setup able to acquire large-format images and spectra. Excellent homogeneity has been observed. Energy resolution as low as 127 eV FWHM at 5.9 keV has been obtained including all single events of the matrix back illuminated at -45<;°C and read out at a 300-frames/s rate. This paper presents experimental methods and results.

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An integrating solid state detector with segmentation has been developed that addresses the needs in scanning transmission x-ray microscopy below 1 keV photon energy. The detector is not cooled and can be operated without an entrance window which leads to a total photon detection efficiency close to 100%. The chosen segmentation with 8 independent segments is matched to the geometry of the STXM to maximize image mode flexibility. In the bright field configuration for 1 ms integration time and 520 eV x-rays the rms noise is 8 photons per integration.

256 Pixel DEPFET Detectors for X-Ray Astronomy

The High Time Resolution Spectrometer (HTRS) is one of the five focal plane instruments of the International X-ray Observatory (IXO). The HTRS is the only instrument matching the top level mission requirement of handling a one Crab X-ray source with an efficiency greater than 10%. It will provide IXO with the capability of observing the brightest X-ray sources of the sky, with sub-millisecond time resolution, low deadtime, low pile-up (less than 2% at 1 Crab), and CCD type energy resolution (goal of 150 eV FWHM at 6 keV). The HTRS is a non-imaging instrument, based on a monolithic array of Silicon Drift Detectors (SDDs) with 31 cells in a circular envelope and a X-ray sensitive volume of 4.5 cm2 x 450 μm. As part of the assessment study carried out by ESA on IXO, the HTRS is currently undergoing a phase A study, led by CNES and CESR. In this paper, we present the current mechanical, thermal and electrical design of the HTRS, and describe the expected performance assessed through Monte Carlo simulations.

NOVEL INTEGRATING SOLID STATE DETECTOR WITH SEGMENTATION FOR SCANNING TRANSMISSION SOFT X-RAY MICROSCOPY.

The main features of silicon drift detector modules currently produced by KETEK GmbH and MPI Halbleiterlabor, Munich will be summarized, giving an overview over state of the art and future possible applications.