Yeping Wang
University of Cologne
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Featured researches published by Yeping Wang.
Proceedings of SPIE | 2008
Thomas Bertram; A. Eckart; Bettina Lindhorst; Steffen Rost; C. Straubmeier; Evangelia Tremou; Yeping Wang; Imke Wank; G. Witzel; Udo Beckmann; M. Brix; Sebastian Egner; T. M. Herbst
LINC-NIRVANA is the near-infrared homothetic imaging camera for the Large Binocular Telescope. Once operational, it will provide an unprecedented combination of angular resolution, sensitivity and field of view. Its Fringe and Flexure Tracking System (FFTS) is mandatory for an efficient interferometric operation of LINC-NIRVANA. It is tailored to compensate low-order phase perturbations in real-time to allow for a time-stable interference pattern in the focal plane of the science camera during the integration. Two independent control loops are realized within FFTS: A cophasing loop continuously monitors and corrects for atmospheric and instrumental differential piston between the two arms of the interferometer. A second loop controls common and differential image motion resulting from changing orientations of the two optical axes of the interferometer. Such changes are caused by flexure but also by atmospheric dispersion. Both loops obtain their input signals from different quadrants of a NIR focal plane array. A piezo-driven piston mirror in front of the beam combining optics serves as actuator in the cophasing loop. Differential piston is determined by fitting a parameterized analytical model to the observed point spread function of a reference target. Tip-tilt corrections in the flexure loop are applied via the secondary mirrors. Image motion is sensed for each optical axis individually in out-of-focus images of the same reference target. In this contribution we present the principles of operation, the latest changes in the opto-mechanical design, the current status of the hardware development.
Proceedings of SPIE | 2006
Thomas Bertram; Carmelo Arcidiacono; C. Straubmeier; Steffen Rost; Yeping Wang; A. Eckart
The correction of atmospheric differential piston and instrumental flexure effects is mandatory for interferometric operation of the LBT NIR interferometric imaging camera LINC-NIRVANA. The task of the Fringe and Flexure Tracking System (FFTS) is to detect and correct these effects in real-time. In the fringe tracking concept that we present, differential piston information is gathered in the image plane by analyzing the PSF of a reference star anywhere in the large field of view of the LBT. We have developed and tested a fast PSF analysis algorithm that allows to clearly identify differential piston even in the case of low S/N. We present performance estimates of the algorithm. Since the performance of the FFTS algorithm has a strong impact on the overall sky coverage of LINC-NIRVANA, we studied the required limiting magnitudes of the fringe tracking reference star for different scenarios. As the FFTS may not necessarily operate on the science target, but rather uses a suitable reference star at a certain angular distance to the science target, differences between piston values at the two positions add to the residual piston of the FFTS. We have dealt with the question of differential piston angular anisoplanatism and studied a possible improvement of the isopistonic patch size by the use of multi-conjugate adaptive optics (MCAO). In its final stage, LINC-NIRVANA will be equipped with such a system.
Proceedings of SPIE | 2008
Steffen Rost; Thomas Bertram; Bettina Lindhorst; C. Straubmeier; Evangelia Tremou; Yeping Wang; G. Witzel; A. Eckart
LINC-NIRVANA is the NIR homothetic imaging camera for the Large Binocular Telescope (LBT). Its Fringe and Flexure Tracking System (FFTS) is mandatory for an efficient interferometric operation of LINC-NIRVANA: the task of this cophasing system is to assure a time-stable interference pattern in the focal plane of the camera. Differential piston effects will be detected and corrected in a real-time closed loop by analyzing the PSF of a guide star at a frequency of 100Hz-200Hz. A dedicated piston mirror will then be moved in a corresponding manner by a piezo actuator. The long-term flexure tip/tilt variations will be compensated by the AO deformable mirrors. A testbed interferometer has been designed to simulate the control process of the movement of a scaled piston mirror under disturbances. Telescope vibration and atmospheric variations with arbitrary power spectra are induced into the optical path by a dedicated piezo actuator. Limiting factors of the control bandwith are the sampling frequency and delay of the detector and the resonance frequency of the piston mirror. In our setup we can test the control performance under realistic conditions by considering the real piston mirrors dynamics with an appropriate software filter and inducing a artificial delay of the PSF detector signal. Together with the expected atmospheric OPD variations and a realistic vibration spectrum we are able to quantify the piston control performance for typical observation conditions. A robust control approach is presented as result from in-system control design as provided by the testbed interferometer with simulated dynamics.
Proceedings of SPIE | 2006
Thomas Bertram; Harald Baumeister; W. Laun; C. Straubmeier; Steffen Rost; Yeping Wang; A. Eckart
The correction of atmospheric differential piston and instrumental flexure effects is mandatory for interferometric operation of the LBT NIR interferometric imaging camera LINC-NIRVANA. The task of the Fringe and Flexure Tracking System (FFTS) is to detect and correct these effects in a real-time closed loop. Being a Fizeau-Interferometer, the LBT provides a large field of view (FoV). The FFTS can make use of the large FoV and increase the sky coverage of the overall instrument if it is able to acquire the light of a suitable fringe tracking reference star within the FoV. For this purpose, the FFTS detector needs to be moved to the position of the reference star PSF in the curved focal plane and needs to precisely follow its trajectory as the field rotates. Sub-pixel (1 pixel = 18.5 micron) positioning accuracy is required over a travel range of 200mm x 300mm x 70mm. Strong are the constraints imposed by the need of a cryogenic environment for the moving detector. We present a mechanical design, in which the Detector Positioning Unit (DPU) is realized with off-the-shelf micro-positioning stages, which can be kept at ambient temperature. A moving baffle will prevent the intrusion of radiation from the ambient temperature environment into the cryogenic interior of the camera. This baffle consists of two nested disks, which synchronously follow any derotation - or repositioning trajectory of the DPU. The detector, its fanout board and a filter wheel are integrated into a housing that is mounted on top of the DPU and that protects the FFTS detector from stray light. Long and flexible copper bands allow heat transfer from the housing to the LINC-NIRVANA heat exchanger.
Proceedings of SPIE | 2006
Yeping Wang; Thomas Bertram; C. Straubmeier; Steffen Rost; A. Eckart
The correction of atmospheric differential piston and instrumental flexure effects is mandatory for optimum interferometric performance of the LBT NIR interferometric imaging camera LINC-NIRVANA. The task of the Fringe and Flexure Tracking System (FFTS) is to detect and correct these effects in a real-time closed loop. On a timescale of milliseconds, image data of the order of 4K bytes has to be retrieved from the FFTS detector, analyzed, and the results have to be sent to the control system. The need for a reliable communication between several processes within a confined period of time calls for solutions with good real-time performance. We investigated two soft real-time options for the Linux platform. The design we present takes advantage of several features that follow the POSIX standard with improved real-time performance, which were implemented in the new Linux kernel (2.6.12). Several concepts, such as synchronization, shared memory, and preemptive scheduling are considered and the performance of the most time-critical parts of the FFTS software is tested.
Proceedings of SPIE | 2006
C. Straubmeier; Thomas Bertram; A. Eckart; Steffen Rost; Yeping Wang; T. M. Herbst; Roberto Ragazzoni; G. Weigelt
LINC-NIRVANA is the interferometric near-infrared imaging camera for the Large Binocular Telescope (LBT). Being able to observe at wavelength bands from J to K (suppported by an adaptive optics system operating at visible light) LINC-NIRVANA will provide an unique and unprecedented combination of high angular resolution (~ 9 milliarcseconds at 1.25μm), wide field of view (~ 100 arcseconds2 at 1.25μm), and large collecting area (~ 100m2). One of the major contributions of the 1. Physikalische Institut of the University of Cologne to this project is the development and provision of the Fringe and Flexure Tracking System (FFTS). In addition to the single-eye adaptive optics systems the FFTS is a crucial component to ensure a time-stable wavefront correction over the full aperture of the double-eye telescope, a mandatory pre-requisite for interferometric observations. Using a independent HAWAII 1 detector array at a combined focus close to the science detector, the Fringe and Flexure Tracking System analyses the complex two-dimensional interferometric point spread function (PSF) of a suitably bright reference source at frame rates of up to several hundred Hertz. By fitting a parameterised theoretical model PSF to the preprocessed image-data the FFTS determines the amount of pistonic phase difference and angular misalignment between the wavefronts of the two optical paths of LINC-NIRVANA. For every exposure the corrective parameters are derived in real-time and transmitted to a dedicated piezo-electric fast linear mirror for simple path lengths adjustments, and/or to the adaptive optics systems of the single-eye telescopes for more complicated corrections. In this paper we present the basic concept and currect status of the opto-mechanical design of the Fringe and Flexure Tracker, the operating principle of the fringe and flexure tracking loops, and the encouraging result of a laboratory test of the piston control loop.
Proceedings of SPIE | 2008
Thomas Bertram; Bettina Lindhorst; Evangelia Tremou; Steffen Rost; Yeping Wang; Imke Wank; G. Witzel; C. Straubmeier; A. Eckart
LINC-NIRVANA is the NIR homothetic imaging camera for the Large Binocular Telescope (LBT). Its Fringe and Flexure Tracking System (FFTS) is mandatory for an effcient interferometric operation of LINC-NIRVANA: the task of this cophasing system is to assure a time-stable interference pattern in the focal plane of the camera. A testbed interferometer, set up as laboratory experiment, is used to develop the FFTS control loop and to test the robustness of the fringe tracking concept. The geometry of the resulting interferometric intensity distribution in the focal plane of the implemented CCD corresponds to that of the LBT PSF. The setup allows to produce monochromatic (He-Ne laser) and polychromatic (halogen lamp) PSFs and allows to actively introduce well defined low-order phase perturbations, namely OPD and differential tip/tilt. Furthermore, all components that are required in a fringe tracking servo loop are included: a sensor for fringe acquisition and an actuator to counteract measured OPD. With this setup it is intended to determine the performance with which a fringe tracking control loop is able to compensate defined OPD sequences, to test different control algorithms, and to optimize the control parameters of an existing servo system. In this contribution we present the design and the realization of the testbed interferometer. Key parameters describing the white light testbed interferometer, such as fringe contrast and thermal sensitivity are discussed. The effects of all controllable phase perturbations are demonstrated.
Proceedings of SPIE | 2006
Florian Briegel; Jürgen Berwein; Frank Kittmann; Valentin V. Volchkov; Lars Mohr; Wolfgang Gaessler; Thomas Bertram; Steffen Rost; Yeping Wang
The MPIA is leading an international consortium of institutes in building an instrument called LINC-NIRVANA, the LBT INterferometric Camera and Near-IR / Visible Adaptive INterferometer for Astronomy. LINC-NIRVANA is a Fizeau interferometer for the Large Binocular Telescope doing imaging in the near infrared (J, H, K - band). Multi-conjugated adaptive objects is used to increase sky coverage and to get diffraction limited images over a 2 arcminute field of view. The LN Common Software provides a software infrastructure common to all partners and consists of a documented collection of common patterns in control systems and of services, which implement those patterns. The heart of LCSW is an object model of controlled devices, implemented as ICE network objects. A code generator creates application from templates for these network objects.
Astronomical Telescopes and Instrumentation | 2003
C. Straubmeier; A. Eckart; Thomas Bertram; Lahbib Zealouk; Yeping Wang
The I. Physikalische Institut of the University of Cologne is participating in an international collaboration with the Max-Planck-Institut fur Astronomie in Heidelberg and the Osservatorio Astrofisico di Arcetri for the development of LINC/NIRVANA, the Near-Infrared/Visible Interferometric Camera for the Large Binocular Telescope (LBT). LINC/NIRVANA will be one of the two interferometric camera systems of the LBT and will operate at wavelengths from 0.6 μm to 2.4 μm, with the long wavelength regime between 1.0 μm and 2.5 μm being covered by LINC (LBT INterferometric Camera} and the shorter wavelengths part from 0.6 μm to 1.0 μm being processed by NIRVANA (Near-InfraRed/Visible Adaptive iNterferometer for Astronomy}. The main contributions of the Cologne institute to this camera will be the 77K dewar and the Fringe and Flexure Tracker (FFT) for the near-infrared part on the system. Detecting and correcting the fast pistonic aberrations of the atmosphere and the slow flexure of the instrument in a closed-loop operation, the presence and proper function of the FFT is mandatory for a time-stable image quality at highest interferometic resolutions. In order to get the best possible image correction for LINC, the FFT will be located inside the camera dewar at an interferometric focus close the one of the near-infrared science detector. Using simple optical elements it will continuously monitor the time-variable phase difference and pupil locations of the incoming wavefronts from the two arms of the twin-telescope. In this article we give a short overview of the camera concept of LINC and present the current status of the design and development of the FFT going on at our institute at the University of Cologne.
Comptes Rendus Physique | 2005
Wolfgang Gaessler; Carmelo Arcidiacono; Sebastian Egner; T. M. Herbst; Dave Andersen; Harald Baumeister; Peter Bizenberger; Hermann Boehnhardt; Florian Briegel; Martin Kuerster; W. Laun; Lars Mohr; B. Grimm; H.-W. Rix; R.-R. Rohloff; Roberto Soci; Clemens Storz; Wenli Xu; Roberto Ragazzoni; Piero Salinari; Emiliano Diolaiti; Jacopo Farinato; M. Carbillet; L. Schreiber; A. Eckart; Thomas Bertram; C. Straubmeier; Yeping Wang; Lahbib Zealouk; G. Weigelt