Profiling structured beams produced by X-ray free-electron lasers (FELs) is crucial to both maximizing signal intensity for weakly scattering targets and interpreting their scattering patterns. Earlier ablative imprint studies describe how to infer the X-ray beam profile from the damage that an attenuated beam inflicts on a substrate. However, the beams in-situ profile is not directly accessible with imprint studies because the damage profile could be different from the actual beam profile. On the other hand, although a Shack-Hartmann sensor is capable of in-situ profiling, its lenses may be quickly damaged at the intense focus of hard X-ray FEL beams. We describe a new approach that probes the in-situ morphology of the intense FEL focus. By studying the translations in diffraction patterns from an ensemble of randomly injected sub-micron latex spheres, we were able to determine the non-Gaussian nature of the intense FEL beam at the Linac Coherent Light Source (SLAC National Laboratory) near the FEL focus. We discuss an experimental application of such a beam-profiling technique, and the limitations we need to overcome before it can be widely applied.
The Max Planck Advanced Study Group (ASG) at the Center for Free Electron Laser Science (CFEL) has
designed the CFEL-ASG MultiPurpose (CAMP) instrument, which provides a unique combination of particle
and photon detectors for experiments at 4th generation light sources. In particular, CAMP includes two sets
of newly developed 1024 × 1024 pixel pnCCD imaging detector systems. The CAMP instrument has now been
successfully employed during the first three beam times at LCLS, and we report here on practical experience
gained for the operation of imaging pnCCD detectors at FEL facilities. We address a wide range of topics:
pnCCD gain and energy calibration during experiments; suppression of optical light contamination in pumpprobe
experiments; contamination of the pnCCD entrance window with sample material; effects of accidental
direct impact on the pnCCDs of particles generated by the FEL beam impinging on the experimental setup; and
the effect of accidental direct exposure of a pnCCD to the focused and unattenuated X-ray beam. These lessons
learned will help us to further improve operation of pnCCDs in future FEL experiments.
Results of coherent diffractive imaging experiments performed with soft X-rays (1-2 keV) at the Linac Coherent
Light Source are presented. Both organic and inorganic nano-sized objects were injected into the XFEL beam
as an aerosol focused with an aerodynamic lens. The high intensity and femtosecond duration of X-ray pulses
produced by the Linac Coherent Light Source allow structural information to be recorded by X-ray diffraction
before the particle is destroyed. Images were formed by using iterative methods to phase single shot diffraction
patterns. Strategies for improving the reconstruction methods have been developed. This technique opens
up exciting opportunities for biological imaging, allowing structure determination without freezing, staining or
Measurement campaigns of the Max-Planck Advanced Study Group (ASG) in cooperation with the Center for
Free Electron Laser Science (CFEL) at DESY-FLASH and SLAC-LCLS have established pnCCDs as universal
photon imaging spectrometers in the energy range from 90 eV to 2 keV. In the CFEL-ASG multi purpose
chamber (CAMP), pnCCD detector modules are an integral part of the design with the ability to detect photons
at very small scattering angles. In order to fully exploit the spectroscopic and intensity imaging capability of
pnCCDs, it is essentially important to translate the unprocessed raw data into units of photon counts for any
given position on the detection area.
We have studied the performance of pnCCDs in FEL experiments and laboratory test setups for the range
of signal intensities from a few X-ray photons per signal frame to 100 or more photons with an energy of 2 keV
per pixel. Based on these measurement results, we were able to characterize the response of pnCCDs over the
experimentally relevant photon energy and intensity range. The obtained calibration results are directly relevant
for the physics data analysis. The accumulated knowledge of the detector performance was implemented in
guidelines for detector calibration methods which are suitable for the specific requirements in photon science
experiments at Free Electron Lasers.
We discuss the achievable accuracy of photon energy and photon count measurements before and after the
application of calibration data. Charge spreading due to illumination of small spots with high photon rates is
discussed with respect to the charge handling capacity of a pixel and the effect of the charge spreading process
on the resulting signal patterns.
New generation synchrotron light sources, the X-ray free electron lasers, require a two dimensional focal plane
instrumentation to perform X-ray imaging from below 100eV up to 25keV. The instruments have to face the accelerator
bunch structure and energy bandwidth which is different for existing (FLASH, Hamburg and LCLS, Menlo Park) and
future photon sources (SACLA, Harima and XFEL, Hamburg). Within the frame of the Center for Free Electron Laser
Science (CFEL), a joint effort of the Max-Planck Society, DESY and the University of Hamburg, the MPI
semiconductor laboratory developed, produced and operated large area X-ray CCD detectors with a format of nearly
60cm2 image area. They show outstanding characteristics: a high readout speed due to a complete parallel signal
processing, high and homogeneous quantum efficiency, low signal noise, radiation hardness and a high pixel charge
handling capacitance. We will present measurement results which demonstrate the X-ray spectroscopic and imaging
capabilities of the fabricated devices.
We will also report on the concept and the anticipated properties of the full, large scale system. The implementation of
the detector into an experimental chamber to perform measurements e.g. of macromolecules in order to determine their
structure at atomic resolutions will be shown.
The new X-ray telescope eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the main
instrument on the Russian new Spectrum-RG satellite, scheduled for launch in 2012. The primary scientific goal
of eROSITA is the detection of about 100,000 clusters of galaxies in an all sky survey. This allows a systematic
study on the large scale structures in the universe and will give new information about the nature of dark energy.
The focal plane detector is a 5 cm × 3 cm framestore PNCCD, an advanced successor of the XMM-Newton
PNCCD, designed and fabricated at the MPI Halbleiterlabor. It has 384 × 384 pixels of 75 μm × 75 μm in the
image area and will provide high position, time and spectral resolution as well as a high quantum efficiency for
X-ray photons in the energy range from 0.2 keV up to 10 keV. The first flight-like CCDs have been finished in
2008. In order to extensively test these new PNCCDs we developed an electronic test-setup. It is very versatile,
allowing us to test the CCDs under many different conditions and is appropriate to show at the same time
excellent performance of the detector. In this contribution we present in detail the electronic test-setup, some
test results and the conclusions which can be drawn for the eROSITA flight modules.
A special type of CCD, the so-called PNCCD, was originally developed for the focal plane camera of the XMMNewton
space telescope. After the satellite launch in 1999, the MPI Halbleiterlabor continued the detector development
for various ground-based applications. Finally, a new X-ray PNCCD was designed again for a space telescope named
eROSITA. The space telescope will be equipped with an array of seven parallel oriented X-ray mirror systems of
Wolter-I type and seven cameras, placed in their foci. This instrumentation will permit the exploration of the X-ray
universe in the energy band from 0.3 keV up to 10 keV with a time resolution of 50 ms for a full image comprising
384 x 384 pixels. eROSITA will be accommodated on the new Russian Spectrum-RG satellite. The mission was already
approved by the responsible German and Russian space agencies. The detector development is focussed to fulfil the
scientific specifications for detector performance under the constraints of all the mechanical, power, thermal and
radiation hardness issues for space instrumentation. This considers also the recent change of the satellite's orbit. The
Lagrange point L2 was decided as new destination of the satellite instead of a low-Earth orbit (LEO). We present a
detailed description of the detector system and the current development status. The most recent test results are reported
here. Essential steps for completion of the seven focal plane detectors until satellite launch in 2012 will be itemized.
The German X-ray observatory eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the prime
instrument of the new Spectrum-RG mission. Launch of the Russian satellite is planned for the year 2011. The scientific
goal of eROSITA is primarily the detection and analysis of 100 thousand clusters of galaxies in order to study the large
scale structures in the Universe and to test cosmological models. The therefore required large effective area is obtained
by an array of seven identical and parallel aligned Wolter-I telescopes. In the focus of each mirror module, there is a
large frame store pnCCD detector, providing a field of view of 1° in diameter. The same X-ray detector type will also be
applied for ART-XC, another grazing-incidence telescope system aboard Spectrum-RG, which permits the detection of
heavily obscured X-ray sources. These scientific instruments allow the exploration of the X-ray Universe in the energy
band from 0.3 keV to 11 keV. During a mission time of at least five years, an all-sky survey, wide as well as deep
surveys and pointed observations will be performed. Approval and funding for eROSITA were granted by the German
space agency DLR in April 2007.
The conceptual design of the X-ray focal plane cameras is presented here comprising electrical, thermal, and mechanical
aspects. Key part of the camera is the pnCCD detector chip, which is developed and produced in our semiconductor
laboratory, the MPI Halbleiterlabor. The CCD was designed according to the specifications given by the scientific goals
of eROSITA. The eROSITA CCD differs apparently from all previously produced frame store pnCCDs by its larger
size and format. The CCD image area of the seven eROSITA cameras is in total 58 cm2 large and their number of pixels
is about seven times higher than that of the XMM-Newton pnCCD camera. First pnCCD devices were recently
produced and tested. Their performance measurements and results are of most importance for eROSITA because the
tested CCDs are the control sample of the flight detector production.
An advanced pnCCD type has been developed, based on the concept of the XMM-Newton detector, which has been
performing spectroscopy and imaging since 2000. This new detector is designed according to the requirements of
eROSITA, a new X-ray astronomy mission, to be launched in 2010. The focal plane for each of the seven individual
Wolter telescopes will be equipped with one of these new-type X-ray pnCCDs. In addition to the eROSITA chips, we
have developed CCDs for other applications, e.g. for projects which require smaller pixel sizes. The devices that have
been produced in the semiconductor laboratory (MPI Halbleiterlabor) of the Max-Planck-Institut fur extraterrestrische
Physik are currently subject of systematic quality checks and spectroscopic tests. These tests are performed under
standardized conditions on a representative subset of the many devices we have produced. The aim of these tests is to
extract the key performance parameters of the individual CCDs like readout noise, energy resolution and the occurrence
of bad pixels. The analysis includes the CAMEX analog signal processor, which has been developed for the readout of
the CCD signals. After an introduction, we present the motivation for the detector development and give an overview
about our CCD design and production, as well as about the CAMEX ASIC. Then device tests, test setups and data
analysis are described. We report in detail about the performance of the tested devices. Failures that occurred during
device tests are subsequently discussed. Finally, we give a review of the results.
At MPI Halbleiterlabor, pnCCDs have been continuously developed to improve readout noise, readout speed, charge transfer efficiency and energy resolution. Pixel sizes of 75μm, 51μm and 36μm were realized in addition to the original 150μm pixel design. Reduction of the pixel size evidently changes the electric fields in the pixel structure. This leads to the question of how scaling of the pixel size affects the charge collection at subpixel dimensions. We used the "mesh-method" to measure the amount of signal charge deposited in a pixel depending on the position of X-Ray photon incidence within the pixel. In this experiment, a mesh with a rectangular hole pattern was mounted above the entrance window or structured front side of the detector. A slight rotation of the mesh ensures that every hole has a different position relative to the pixel below. It corresponds to scanning of a single pixel. Measurements were done with pnCCDs of 150μm, 75μm and 51μm pixel size at photon energies from 0.7keV to 5.4keV. We also used a setup with front side illumination of a pnCCD with 75μm pixel size to investigate the absorption of X-ray photons in the register structure of the device. Numerical simulations delivered results for signal charge distribution into pixels along the charge transfer direction. We analyzed the charge collection in a pixel and the absorption properties of the register structure with a spatial resolution below 5μm and could investigate the accuracy of numerical device simulations.
A new generation of pnCCDs has been developed for the proposed X-ray astronomy missions, DUO and ROSITA. The DUO/ROSITA CCD is a frame store pnCCD based on the concept of the XMM-Newton pnCCD and has both, improved performance and new features. This detector permits accurate spectroscopy of X-rays as well as imaging and high time resolution with high quantum efficiency in the energy band from 0.3 keV to 10 keV. Interfering electron-hole pair generation due to optical and UV light is prevented by a deposition of an on-chip filter. We describe the frame store pnCCDs developed and fabricated for the DUO and ROSITA missions in the semiconductor laboratory of the Max-Planck-Institut fuer extraterrestrische Physik. An overview about the CCD concept and design is given along with some details about the fabrication of the devices. In addition, we introduce a new analog signal processor which has been developed specifically for the readout of the frame store pnCCD signals. The main focus of this paper is to present the very first measurements with this CCD type and its analog signal processor. Towards this aim we report the operation of this new sensor and its key performance parameters. Finally we discuss ongoing and future tests with the DUO/ROSITA CCDs.
DUO and ROSITA are two future X-ray astronomy missions observing in the energy band from about 0.3 keV to 10 keV. While the NASA satellite DUO will scan selected areas of the X-ray sky with high sensitivity, the German ROSITA mission shall perform an all-sky survey. Both missions apply an array of seven Wolter telescopes with separated field of views and seven dedicated PN-CCD focal plane detectors. The focal plane detectors are a further development of the flight-proven PN-CCD applied for the XMM-Newton observatory. The advanced device, called 'frame store PN-CCD', is designed and fabricated in the semiconductor laboratory of the Max-Planck-Institute for extraterrestrial physics. An introduction into the detector concept and design are presented as well as the promising results which have been achieved with the prototype devices. This includes an overview about the performance of the PN-CCD and in detail the recent measurements with the detector. An example is the low energy response of the optimized photon entrance window with integrated optical light filter. As the CAMEX analog signal processor chip is a main component of the detector module, we describe its development status. Furthermore, we report about the application of the mesh experiment to the PN-CCD which allows for a study of the electric potential characteristics in the detector bulk, in particular in the charge transfer depth. The information is of great importance for an accurate knowledge about the drift of the generated signal electrons into the potential wells of the pixels.