Lothar Struer

Max Planck Institute for Extraterrestrial Physics, Arching, Bavaria, Germany

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Publications (2)2.28 Total impact

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    ABSTRACT: In the MPI-Halbleiterlabor (MPI-HLL) we are developing fully depleted pn-type Charge Coupled Devices (pnCCD) with a thick radiation-sensitive region. Since 1997, the mesh experiment has been established as an unique technique to determine an X-ray interaction position with subpixel resolution. In order to investigate the signal charge behavior in pnCCDs, we performed the mesh experiment using various characteristic X-ray lines. Cu-L (0.9 keV), Al-K (1.5 keV) and Ti-K (4.5 keV) were used and the device operated under various conditions, e.g. register voltages. We obtained the restored pixel images for various X-ray event patterns. The photon entrance window of the back illuminated pnCCD shows highly uniform detection efficiency within a pixel. We measured the charge cloud size generated by an X-ray photon inside the CCD. The measured charge cloud sizes are around 6 mm (rms) depending on the X-ray energy. The operation with different register conditions revealed asymmetries and regions with a weaker electric field around pixel boundaries. r 2006 Published by Elsevier B.V.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2006; 568(95). · 1.14 Impact Factor
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    ABSTRACT: A special type of charge-coupled device, the pnCCD, has been developed in the nineties as focal-plane detector for the X-ray astronomy mission XMM-Newton of the European Space Agency. The pnCCD detector has been in operation since the satellite launch in 1999. It is performing up to date spectroscopy of X-rays in combination with imaging and high time resolution. The excellent performance of the flight camera is still maintained; in particular, the energy resolution has been nearly constant since launch. In order to satisfy the requirements of future X-ray astronomy missions as well as those of ground-based experiments, a new type of pnCCD has been developed. The 'frame store pnCCD' shows various optimizations in device design and fabrication process. Devices with up to 256  512 pixels have been fabricated in 2004 and recently tested. Simultaneously, a programmable analog signal processor for the readout of the CCD signals, the DUO CAMEX, has been developed. The readout noise of the new detector has a value of 2 electrons ENC which is less than half of the figure of the XMM-Newton pnCCD. We measured an energy resolution that is close to the theoretical limit given by the Fano noise. In particular the low-energy response of the new devices was substantially improved. The quantum efficiency for X-rays is at least 90% in the entire energy band from 0.3 keV up to 11 keV. This is due to the ultra-thin photon entrance window as well as the full depletion of the 450 mm thick back-illuminated pnCCD. The position resolution is better than the pixel sizes of 75 mm  75 mm or 51 mm  51 mm because the signal charge is spread over up to four pixels which allows a more accurate event position determination. 'Out of time' events are substantially reduced to the order of 0.1% by operating the pnCCD in frame store mode. Higher operating temperatures, e.g. À20 1C, are possible due to the smaller thermally generated dark-current level of the new devices and the operation at higher frame rates. Low power consumption applications like for the ROSITA X-ray astronomy mission with low frame rates of, e.g. 20 images/s, as well as high frame rate applications, e.g. 200 images/s, are possible with the same device.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2006; 568(29). · 1.14 Impact Factor