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SPHERE (Spectro-Polarimetric High-contrast Exoplanet Research) is a second generation VLT instrument aimed at the direct detection of exo-planets. It has received its first light in May 2014. ZIMPOL (Zurich Imaging Polarimeter) is the imaging polarimeter subsystem of the SPHERE instrument. It's capable of both high accuracy and high sensitivity polarimetry but can also be used as a classical imager. It is located behind an extreme AO system and a stellar coronagraph. ZIMPOL operates at visible wavelengths which is best suited to detect the very faint reflected and hence polarized visible light from extra solar planets. During the SPHERE fourth commissioning period (October 2014) we have made deep coronagraphic observations of the bright star alpha Gru (mR = 1.75) to assess the high contrast polarimetric performance of SPHERE-ZIMPOL. We have integrated on the target for a total time of about 45 minutes during the meridian transit in the Very Broad Band filter (600 - 900 nm) with a classical Lyot coronagraph with 3 λ/D radius focal mask. We reduce the data by a combination of Polarized Background subtraction, Polarimetric Differential Imaging (PDI) and Angular Differential Imaging (ADI). We reach contrasts of 10-6 and 10-7 at a radial distances of respectively 7 and 14 lambda/D from the PSF core. At these radial distances we are respectively a factor of 10 and 2 above the photon noise limit. We discuss our results by considering the temporal and spatial speckle behavior close to the PSF core in combination with low order polarimetric aberrations. more...

SPHERE (Spectro-Polarimetric High-contrast Exoplanet Research) is a new instrument for the VLT aimed at the direct detection of exo-planets. It has received its first light in May 2014. ZIMPOL (Zurich Imaging Polarimeter) is the imaging polarimeter subsystem of the SPHERE instrument. It's capable of both high accuracy and high sensitivity polarimetry but can also be used as a classical imager. It is located behind an extreme AO system and a stellar coronagraph. ZIMPOL operates at visible wavelengths (600-900 nm) which is best suited to detect the very faint reflected and hence polarized visible light from extra solar planets. It has an instantaneous Field of View of 3 x 3 arcsec2 (extendable to 8 arcsec diameter) with an angular resolution of 14 mili-arcsec. We discuss the results that are obtained from the full SPHERE-ZIMPOL system testing. In particular the optical, polarimetric and high contrast performance. © (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only. more...

ZIMPOL is the high contrast imaging polarimeter subsystem of the ESO SPHERE instrument. ZIMPOL is dedicated to detect the very faint reflected and hence polarized visible light from extrasolar planets. ZIMPOL is located behind an extreme AO system (SAXO) and a stellar coronagraph. SPHERE is foreseen to have first light at the VLT early 2013. ZIMPOL is currently integrated in the SPHERE system and in testing phase. We describe the alignment strategy and the results of the ZIMPOL system and the related alignment of ZIMPOL into SPHERE by the aid of an alignment unit. The field selecting tip/tilt mirror alignment and it’s requirement for perpendicularity to the two detectors is described. The test setup of the polarimetric components is described. SPHERE is an instrument designed and built by a consortium consisting of IPAG MPIA LAM LESIA Fizeau INAF Observatoire de Genève ETH NOVA ONERA and ASTRON in collaboration with ESO.© (2012) COPYRIGHT Society of Photo Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only. more...

The imaging polarimeter ZIMPOL is one of three focal plane instruments of the SPHERE / VLT planet finder. ZIMPOL measures the linear polarization based on a fast modulation – demodulation principle using a charge-shifting technique on a masked CCD for separating the photons with opposite polarization direction. This paper describes the on-chip demodulation and the different detector read-out modes which are implemented for the ZIMPOL polarimeter. Test results are presented which allow an evaluation of the performance of the ZIMPOL CCD detectors. The achievable polarization efficiency is close to expectation and the charge trap correction with the two-phase demodulation mode works well. Other detector effects like bias level variations and read-out patterns can be corrected in the data reduction process. The tests demonstrate that the demodulating CCDs fulfill the requirements for the SPHERE project.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only. more...

SPHERE (Spectro-Polarimetric High Contrast Exoplanet Research) is one of the first instruments which aim for the direct detection from extra-solar planets. The instrument will search for direct light from old planets with orbital periods of several months to several years as we know them from our solar system. These are planets which are in or close to the habitable zone. ZIMPOL (Zurich Imaging Polarimeter) is the high contrast imaging polarimeter subsystem of the ESO SPHERE instrument. ZIMPOL is dedicated to detect the very faint reflected and hence polarized visible light from extrasolar planets. The search for reflected light from extra-solar planets is very demanding because the signal decreases rapidly with the orbital separation. For a Jupiter-sized object and a separation of 1 AU the planet/star contrast to be achieved is on the order of 10-8 for a successful detection. This is much more demanding than the direct imaging of young self-luminous planets. ZIMPOL is located behind an extreme AO system (SAXO) and a stellar coronagraph. SPHERE is foreseen to have first light at the VLT at the end of 2012. ZIMPOL is currently in the subsystem testing phase. We describe the results of verification and performance testing done at the NOVA-ASTRON lab. We will give an overview of the system noise performance, the polarimetric accuracy and the high contrast testing. For the high contrast testing we will describe the impact of crucial system parameters on the contrast performance. SPHERE is an instrument designed and built by a consortium consisting of IPAG, MPIA, LAM, LESIA, Fizeau, INAF, Observatoire de Genève, ETH, NOVA, ONERA and ASTRON in collaboration with ESO. more...

X-shooter is the first second-generation instrument newly commissioned a the VLT. It is a high efficiency single target intermediate resolution spectrograph covering the range 300 - 2500 nm in a single shot. We summarize the main characteristics of the instrument and present its performances as measured during commissioning and the first months of science operations. more...

ZIMPOL is the high contrast imaging polarimeter subsystem of the ESO SPHERE instrument. ZIMPOL is dedicated to detect the very faint reflected and hence polarized visible light from extrasolar planets. ZIMPOL is located behind an extreme AO system (SAXO) and a stellar coronagraph. SPHERE is foreseen to have first light at the VLT at the end of 2011. ZIMPOL is currently in the manufacturing, integration and testing phase. We describe the optical, polarimetric, mechanical, thermal and electronic design as well as the design trade offs. Specifically emphasized is the optical quality of the key performance component: the Ferro-electric Liquid Crystal polarization modulator (FLC). Furthermore, we describe the ZIMPOL test setup and the first test results on the achieved polarimetric sensitivity and accuracy. These results will give first indications for the expected overall high contrast system performance. SPHERE is an instrument designed and built by a consortium consisting of LAOG, MPIA, LAM, LESIA, Fizeau, INAF, Observatoire de Geneve, ETH, NOVA, ONERA and ASTRON in collaboration with ESO. more...

X-shooter is a high-efficiency spectrograph capable of simultaneously observing the complete spectral range of 300- 2500 nm. The instrument will be located at the Cassegrain focus of one of the VLT UTs. To allow sky back ground limited observations the 120 kg Optical Bench of the NIR Spectrograph and the HAWAII-2RG detector are cooled to 105 K and 82 K respectively. To ensure vibrationless operation the cooling is performed by a LN2 bath-cryostat. The thermal stability requirements for the Optical Box are very tight (order of 100 mK) considering that the NIR-cryostat is subject to telescope movement and LN2 level variations. Large glass optics are limiting the cooldown. To speed up the cooldown the cooling concept of the Optical Box includes the utilization of LN2 heat exchangers. To avoid asymptotic stabilizing times the Optical Box is cooled below the operating temperature. When the optics reach a temperature slightly above the operating temperature the temperature of the Optical Box is quickly brought back to stabilize the optics. Dedicated controllers, strapping and heaters are used for temperature stabilization during steady state. A cryostat hold time of 24 hours with the minimum amount of LN2 in view of the tight mass budget requires strict control of the power budget and careful control of the design margins. This is ensured by precise modeling of the temperature behavior. The thermal model is compared with the actual measured thermal behavior. more...

X-shooter is a new high-efficiency spectrograph observing the complete spectral range of 300-2500 nm in a single exposure, with a spectral resolving power R>5000. The instrument will be located at the Cassegrain focus of one of the VLT UTs and consists of three spectrographs: UV, VIS and Near-IR. This paper addresses the design, hardware realization and performance of the Near-IR spectrograph of the X-Shooter instrument and its components. Various optical, mechanical and cryogenic manufacturing and verification techniques are discussed. The cryogenic performance of replicated light weight gratings is presented. Bare aluminium mirrors are produced and polished to optical quality to preserve high shape accuracy at cryogenic conditions. Their manufacturing techniques and performance are both discussed. The cryogenic collimator and dispersion boxes, on which the optical components are mounted, feature integrated baffles for improved stiffness and integrated leaf springs to reduce tension on optical components, thereby challenging 5 axis simultaneous CNC milling capabilities. ASTRON Extreme Light Weighting is used for a key component to reduce the flexure of the cryogenic system; some key numbers and unique manufacturing experience for this component are presented. The method of integrated system design at cryogenic working temperatures and the resulting alignment-free integration are evaluated. Finally some key lab test results for the complete NIR spectrograph are presented. more...