We present the properties of the adaptive optics (AO) system of the German 1.5m solar telescope GREGOR, located on the island of Tenerife, Spain. The conventional AO system uses a correlating Shack-Hartmann-Sensor with a 92mm subaperture size and a 256-actuator stacked-piezo deformable mirror (DM). AO performance results and practical experience based on the last four years of operation are presented. A recently installed second wavefront sensor with exchangeable lenslets / subaperture sizes in combination with an EM-CCD camera is used for low light observations such as polarimetric measurements of the solar system planets. Further developments include algorithmic improvements, the use of the night-time sensor for solar (off-limb) observations and solar MCAO.
A multi-conjugate adaptive optics systems has been deployed at the 1.5-meter solar telescope GREGOR for on-sun experiments of MCAO in November 2013. GREGOR MCAO incorporates three deformable mirrors (DMs) conjugate to 0, 8, and 25 km line of sight distance. Two correlating Shack-Hartmann wavefront sensor units are deployed: a high-order on-axis wavefront sensor (OA-WFS) with 10-cm subapertures and 10 arcsec field of view, and a low-order multi-direction wavefront sensor (MD-WFS) with 50-cm subapertures that sample the wavefront in 19 guide regions distributed over one arcminute. The MCAO loop was closed repeatedly in November ’13, as well as in January and May ’14. However, in particular strong static aberrations that were not removed well by the system, derogated the image in the MCAO compensated focal plane. GREGOR MCAO is now permanently installed and available for experiments that shall advance the development of solar MCAO.
We present recent experimental results obtained with CILAS deformable mirrors (DMs) or demonstration prototypes in solar and night-time astronomy (with ground-based telescopes) as well as observation of the Earth (with space telescopes). These important results have been reached thanks to CILAS technology range composed of monomorph and piezostack deformable mirrors, drivers and optical coatings. For instance, the monomorph technology, due to a simple architecture can offer a very good reliability for space applications. It can be used for closed or open loop correction of the primary mirror deformation (thermal and polishing aberrations, absence of gravity). It can also allow a real-time correction of wavefront aberrations introduced by the atmosphere up to relatively high spatial and temporal frequencies for ground-based telescopes. The piezostack technology is useful for very high order correction at high frequency and under relatively low operational temperature (down to -30°C), which is required for future Extremely Large Telescopes (ELTs). This wide range of applications is exposed through recent examples of DMs performances in operation and results obtained with breadboards, allowing promising DMs for future needs.
Since several years the Zurich Imaging polarimeter (ZIMPOL) system is successfully used as a high sensitivity
polarimeter. The polarimeter system, which is mainly based on a fast modulator and a special demodulating
camera with a masked CCD, has been continuously improved. The third version of the system (ZIMPOL-3) is
routinely used at IRSOL, Locarno. The fast modulation allows to “freeze” intensity variations due to seeing,
and to achieve a polarimetric sensitivity below 10<sup>-5</sup> if the photon statistics is large enough. In October 2013
the ZIMPOL system has been brought and installed for the first time at the GREGOR telescope in Tenerife for
a spectropolarimetric observing campaign. There, the system configuration took advantage from the calibration
unit installed at the primary focus of the GREGOR telescope, while the analyzer was inserted in the optical
path just before the spectrograph slit after several folding mirrors. This setup has been tested successfully by
the authors for the first time in this occasion.
Observing the Sun with high angular resolution is difficult because the turbulence in the atmosphere is strongest during day time. In this paper we describe the principles of solar adaptive optics exemplified by the two German solar telescopes VTT and GREGOR at the Observatorio del Teide. With theses systems we obtain near diffraction limited images of the Sun. Ways to overcome the limits of conventional AO by applying multiconjugate adaptive optics (MCAO) are shown.
The Photospheric and Helioseismic imager (PHI) on board of the ESA mission Solar Orbiter, to be launched in 2017,
will provide measurements with high polarimetric accuracy of the photospheric solar magnetic field at high solar
latitudes. The needed pointing precision requires an image stabilisation (ISS) to compensate for spacecraft jitter. The
image stabilisation system works as a correlation tracker with a high-speed camera and a fast steerable mirror. The optomechanical
and electronic design of the system will be presented.
The European Solar Telescope (EST) is a 4-m class solar telescope to be located in the Canary Islands which is currently
in its conceptual design study. EST is a pan-european project (with 29 partners, plus 7 collaborating institutions, from 14
countries) promoted by the European Association for Solar Telescopes (EAST). In the current concept, the main
telescope and its transfer optics assemblies 14 mirrors to provide a Science Coudé Focus with an F/50 telecentric beam.
It is diffraction-limited in a FOV of 1 arcmin with an unvignetted FOV of 2'x2'. The whole system is being optimized in
throughput for several instruments observing simultaneously in a spectral range from 0.39 μm to 2.3 μm. Its innovative
concept integrates an optical transfer stage assembling multiconjugated adaptive optics with optical field de-rotation and
with a perfect balance of the whole system in terms of polarization being also time and wavelength invariant.
Seeing measurements are crucial for the optimum design of (multi-conjugate) adaptive optics systems operating at solar
telescopes. For the design study of the 4-meter European Solar Telescope, to be located in the Canary Islands, several
instruments have been constructed and operated, at the Observatorio del Roque de los Muchachos (La Palma) and at the
Observatorio del Teide (Tenerife), to measure the properties of the ground layer and medium-high altitude turbulence.
Several units of short (42.34 cm) and two long (323.06 cm) scintillometer bars are, or are to be, installed at both
observatories. In addition to them, two wide-field wavefront sensors will be attached to the optical beams of the Swedish
tower, on La Palma, and of the German VTT, on Tenerife, simultaneously used with the normal operation of the
telescopes. These wavefront sensors are of Shack-Hartmann type with ~1 arcminute field of view. In this contribution,
the instruments setup and their performance are described.
The European Solar Telescope (EST) is a pan-european project (with 29 partners, plus 7 collaborating institutions, from
14 countries) for the conceptual design study of a 4-meter class solar telescope promoted by the European Association
for Solar Telescopes (EAST) to be located in the Canary Islands. The telescope, in the conceptual study, provides a
Coudé focus with an F/50 telecentric beam. It is diffraction-limited in a FOV of 1 arcmin and it will be optimized in
throughput for several instruments observing simultaneously in a spectral range from 0.39 μm to 2.3 μm. Its innovative
concept integrates an optical transfer stage assembling multiconjugated adaptive optics with optical field de-rotation and
with a perfect balance of the whole system in terms of polarization being time and wavelength invariant.
We present the setup including optics and components, the reconstruction scheme and performance estimations
of an Adaptive Optics (AO) system implemented at the 1m telescope of the ESA Optical Ground Station (OGS),
Observatorio del Teide, Tenerife. The system will be used to improve the signal-to-noise ratio of satellite to ground
laser communications. It operates with coherent laser communication systems at 1064nm. The wavefront sensor
is an 88-element Shack-Hartmann-sensor (11 subapertures across the pupil), matched to a 12×12 actuator
"Multi-DM" membrane deformable mirror (DM). The system is able to remove a large part of the turbulence-induced
and static wavefront errors by using more than 90 degrees of freedom ("modes"). Due to a special high speed
infrared camera, the control loop can run at speeds up to 20 kHz, achieving a 0db bandwidth of about 500Hz,
depending on the received laser power.
We give an overview of the Adaptive Optics (AO) and Multi-conjugate Adaptive Optics (MCAO) system of the
planned 4m European Solar Telescope (EST). The parameter space and the problems of solar MCAO working
in the visible are explained. The wavefront reconstruction schemes presently being considered are explained.
First estimates of the expected MCAO performance for varying parameter sets are given.
A consortium of more than 20 European solar physics institution from 15 different countries is conducting a design
study for a 4 m class solar telescope which shall be situated at the Canary Islands. In this paper we introduce the AO and
MCAO design concept for EST. A ground layer deformable mirror is combined with an arrangement of four deformable
layer mirrors. A combination of Shack-Hartmann wave front sensors with wide and narrow fields of view is used to
control the system and to achieve a corrected field of view of one arcmin.
India is planning a new solar telescope with an aperture of 2-m for carrying out high resolution studies of the Sun. Site
characterization is underway at high altitude locations in the Himalayan mountains. A detailed concept design for NLST
(National Large Solar Telescope) has been completed. The optical design of the telescope is optimized for high optical
throughput and uses a minimum number of optical elements. A high order AO system is integrated part of the design that
works with a modest Fried's parameter of 7-cm to give diffraction limited performance. The telescope will be equipped
with a suite of post-focus instruments including a high resolution spectrograph and a polarimeter. NLST will also be
used for carrying out stellar observations during the night. The mechanical design of the telescope, building, and the
innovative dome is optimized to take advantage of the natural air flush which will help to keep the open telescope in
temperature equilibrium. After its completion (planned for 2014), NLST will fill a gap in longitude between the major
solar facilities in USA and Europe, and it will be for years the largest solar telescope in the world
With the integration of a 1-meter Cesic primary mirror the GREGOR telescope pre-commissioning started. This is the
first time, that the entire light path has seen sunlight.
The pre-commissioning period includes testing of the main optics, adaptive optics, cooling system, and pointing system.
This time was also used to install a near-infrared grating spectro-polarimeter and a 2D-spectropolarimeter for the visible
range as first-light science instruments. As soon as the final 1.5 meter primary mirror is installed, commissioning will be
completed, and an extended phase of science verification will follow. In the near future, GREGOR will be equipped with
a multi-conjugate adaptive optics system that is presently under development at KIS.
The European Solar Telescope is a project for a 4-meter class telescope to be located in the Canary Islands. EST is
promoted by the European Association for Solar Telescopes (EAST). This is a consortium formed by a number of
research organizations from fifteen European countries (Austria, Croatia, Czech Republic, France, Germany, Hungary,
Italy, the Netherlands, Norway, Poland, Slovak Republic, Spain, Sweden, Switzerland, and United Kingdom). EST will
specialize in high spatial and temporal resolution using diverse instruments that can efficiently produce two-dimensional
spectropolarimetric information of the thermal, dynamic and magnetic properties of the plasma over many scale heights
in the solar atmosphere. In this contribution, the status of the development of the Design Study of EST is presented,
emphasizing the most important aspects of the optical design, mechanical structure, AO and MCAO systems for
wavefront correction, instruments and polarization analysis.
Solar observations are performed over an extended field of view and the isoplanatic patch over which conventional
adaptive optics (AO) provides diffraction limited resolution is a severe limitation. The development of multi-conjugate
adaptive optics (MCAO) for the next generation large aperture solar telescopes is thus a top priority. The Sun is an ideal
object for the development of MCAO since solar structure provides multiple "guide stars" in any desired configuration.
At the Dunn Solar Telescope (DST) we implemented a dedicated MCAO bench with the goal of developing wellcharacterized,
operational MCAO. The MCAO system uses two deformable mirrors conjugated to the telescope
entrance pupil and a layer in the upper atmosphere, respectively. The high altitude deformable mirror can be placed at
conjugates ranging from 2km to 10km altitude. We have successfully and stably locked the MCAO system on solar
granulation and demonstrated the MCAO system's ability to significantly extend the corrected field of view. We present
results derived from analysis of imagery taken simultaneously with conventional AO and MCAO. We also present first
results from solar Ground Layer AO (GLAO) experiments.
This paper describes the flight control software of the wave-front correction system that flew on the 2009 science
flight of the Sunrise balloon telescope. The software discussed here allowed fully automated operations of the
wave-front sensor, communications with the adaptive optics sub-system, the pointing system, the instrument
control unit and the main telescope controller. The software was developed using modern object oriented
analysis and design techniques, and consists of roughly 13.000 lines of C++ code not counting code written for
the on-board communication layer. The software operated error free during the 5.5 day flight.
We present the latest concept of the multi-conjugate adaptive optics system for the 1.5-meter solar telescope Gregor. This
system will employ three deformable mirrors in order to compensate for seeing introduced by the ground layer, and by
shear winds in 5 and 15 km above the telescope ground. Thus, the compensated field of view will grow compared to ground
layer compensation only. We describe the design and the used components and present a testbed which is used to improve
control algorithms and to test all the components before installing them at the Gregor telescope.
The 1m balloon-borne solar telescope Sunrise will be equipped with a wave-front sensing system for automatic in-flight focusing and alignment of the telescope and for high-precision image tracking. A six-element wavefront sensor measures low order aberrations of the telescope, including defocus and coma. The correction is achieved by moving the focusing mirror and the telescope secondary, respectively, in a closed-loop circuit. The same system measures image motion. The instrument requirements for the tracking are a dynamical range of about 30 Hz and a precision of about 0.005 arcs in the sky. The image motion signal feeds a closed-loop control system that drives both the tip-tilt mirror assembly and the mirrors that are needed for focusing and alignment. The tip-tilt unit is a dual-stage system, built at the Kiepenheuer-Insitut, consisting of a slow component with a large range of about 60 arcs and a fast component with a short range and high bandwidth. A breadboard-version of the Correlating Wavefront Sensor has been successfully tested at the German Vacuum Tower Telescope on Tenerife in summer of 2005. A closed-loop bandwidth of 80 Hz was measured for the tracking system. The wave-front sensor detected image aberrations pre-set by the telescope's adaptive optics system with the required accuracy. Sunrise will be flown in long duration stratospheric balloon flights, with a first scientific flight in 2009.
After the successful demonstration of the solar multi-conjugate adaptive optics (MCAO) system at the German 70cm Vacuum Tower Telescope (VTT), Observatorio del Teide, Tenerife, in the last years, we are continuing the development of the system as a testbed for the future MCAO of the 150cm GREGOR solar telescope. We describe an improved reconstruction scheme that increases the number of
corrected off-axis degrees of freedom and will be tested at the VTT
in September 2006. We present a modified optical setup of the GREGOR MCAO that has the advantage of being adjustable to a wide height range of the turbulence.
The integration of the three main silicon carbide mirrors into the new 1.5 m solar telescope GREGOR at Izana on Tenerife, Spain is planned during 2006. We expect first light at the end of 2006. A progress report about integration of the optics and mechanics and planning of the commissioning phase of the telescope and post focus instruments will be presented at the meeting. The GREGOR telescope is build by a consortium of the Kiepenheuer Institut fur Sonnenphysik in Freiburg, the Astrophysikalische Institut Potsdam, the Institut fur Astronomie Gottingen and additional national and international Partners.
The new German solar 1.5 m telescope (GREGOR) will be equipped with an adaptive optic system. GREGOR has a relatively complicated optical scheme with small tolerances. We therefore have to expect certain aberrations due to misalignments and mechanical/optical imperfections. This is why the AO will play an important role as an auxiliary tool for telescope alignment from the very beginning of the commissioning phase. The paper will cover the alignment strategies taking advantage of the AO system.
SUNRISE is an international project for the development, construction, and operation of a balloon-borne solar telescope with an aperture of 1 m, working in the UV/VIS spectral domain. The main scientific goal of SUNRISE is to understand the structure and dynamics of the magnetic field in the atmosphere of the Sun. SUNRISE will provide near diffraction-limited images of the photosphere and chromosphere with an unpredecented resolution down to 35 km on the solar surface at wavelengths around 220 nm. The focal-plane instrumentation consists of a polarization sensitive spectrograph, a Fabry-Perot filter magnetograph, and a phase-diverse filter imager working in the near UV. The first stratospheric long-duration balloon flight of SUNRISE is planned in Summer 2009 from the swedish ESRANGE station. SUNRISE is a joint project of the german Max-Planck-Institut fur Sonnensystemforschung (MPS), Katlenburg-Lindau, with the Kiepenheuer-Institut fur Sonnenphysik (KIS), Freiburg, Germany, the High-Altitude Observatory (HAO), Boulder, USA, the Lockheed-Martin Solar and Astrophysics Lab. (LMSAL), Palo Alto, USA, and the spanish IMaX consortium. In this paper we will present an actual update on the mission and give a brief description of its scientific and technological aspects.
The telescope structure including control system and the complete retractable dome of the new 1.5 m solar telescope GREGOR were assembled during 2004 at Izana on Tenerife, Spain. The GREGOR telescope is build by a consortium of the Kiepenheuer Institut fuer Sonnenphysik, the Astrophysikalische Institut Potsdam, the Institut fuer Astrophysik Goettingen and additional national and international Partners. Pointing, tracking and thermal tests were made to verify the proposed performance. The results of these tests and a progress report of the project will be presented.
We present the optical setup, reconstruction scheme and observational results of the Multi-conjugate Adaptive Optics (MCAO) system at the German 70cm Vacuum Tower Telescope, Observatorio del Teide, Tenerife. The system serves as a testbed for the future MCAO of the new 1.5m GREGOR solar telescope and is an extension of the conventional Adaptive Optics (CAO) system. We demonstrate that the use of one additional MCAO wavefront sensor and one additional deformable mirror increases the corrected field of view from 10 to 35 arcseconds.
We present the optical setup and properties of the second-generation adaptive optics (AO) for the 1.5 m solar telescope GREGOR. The system will consist of a high order AO system correcting about 200 degrees of freedom on-axis at a bandwith of 200 Hz and a multi-conjugate (MCAO) extension that uses one additional deformable mirror to correct the low-order aberrations across a field of one arcminute at a bandwidth of 50 Hz. Diffraction limited observations will be possible for seeing better than 1.2 arcsec. First light is expected in 2007.
GREGOR is the new 1.5 m solar telescope assembled on Tenerife, Spain, by the German consortium of the Kiepenheuer Institut fur Sonnenphysik, the Astronomischen Institut Potsdam, the Universitats-Sternwarte Gottingen and other national and international Partners. The refurbishment of the building is almost finished. The manufacturing of the telescope structure and the optics is still in progress. After the integration of the new complete retractable dome in July 2004 the telescope structure, optic and post focus instruments will be assembled during the rest of the year. First light is planned during May 2005.
SUNRISE is a 1m solar telescope for the visible and near UV wavelength range. It will be flown in long duration stratospheric
balloon flights in Antarctica, with a first scientific flight in 2007. In this paper, we describe the development of a wave-front sensing system that will be used for the automatic in-flight alignment of the SUNRISE telescope and for high-precision
tracking. The system is based on the principles of an adaptive optics system. A 19-element wavefront sensor is used to determine low order aberrations of the telescope, including defocus and spherical aberrations. The correction is achieved by controlling the position of the telescope secondary and a focusing mirror in closed-loop. In addition to these quasi-static aberrations, the system will also measure image motion with a dynamical range of at least 30 Hz and with a precision of about 0.005 arcs. To this end, the image displacement measured in all sub-apertures is averaged and used as
tip-tilt correction signal. This signal will feed a second closed-loop system that drives the tip-tilt mirror assembly. The
tip-tilt mirror unit is designed as a dual-stage system that consists of a slow component with a large range of 60 arcs and a fast component with high bandwidth.
The optical and thermal design of the 1.5 m solar telescope GREGOR is presented. The three first main mirrors of GREGOR will be made from Cesic, a silicon carbide material. One major constraint of large solar telescopes is the thermal load of the structure and the mirrors. The mirrors are heated by the solar radiation and introduce potentially harmful mirror seeing. GREGOR will use an active mirror cooling system and an open telescope structure to reduce these negative effects. A thermal analysis shows that the equilibrium temperature of the Cesic Mirror without active cooling is 6° above ambient temperature. Additional cooling will reduce the temperature difference of the optical surface and ambient air to below 0.1° K. With tempered airflow (about 2.5 m<sup>3</sup>/s per square meter mirror surface) the temperature gradient on the surface of the face sheet is less than 0.1°K. The telescope will have an open structure and a complete retractable dome to support mirror and structure cooling by wind.
We are completing the integration of a solar adaptive optics system KAOS at the 70 cm diameter Vacuum Tower telescope (VTT) on Tenerife. The system is capable to compensate some 30 modes of wavefront aberration with closed-loop bandwidth of about 100 Hz anywhere on the solar disk. We describe the design goals, the main characteristics of KAOS and present a first demonstration of its performance.
The new 1.5 m high resolution telescope will be build up on the reused solar tower of the German 45 cm Gregory Coude Telescope at the Teide Observatory, Izana, Tenerife. The new telescope is a Gregory type with open telescope structure, alt-azimuth mount, complete retractable dome, and a pool of well established and new developed post focus instruments. An adaptive optics system provides the capability for diffraction limited observations at visible wavelengths and the polarimetry device in the secondary focus reduces the perturbation due to instrumental polarization in an efficient way. We describe the main optical characteristics and the focal plane instrumentation with respect to the latest status of the project.
We present an overview of the optical setup and control algorithms for the multi-conjugate adaptive optics (MCAO) system of the 70cm German Vacuum Tower Telescope (VTT), Observatorio del Teide, Tenerife. The system is designed to remove the strong differential tip/tilt of the present AO system across a field of 30 arcseconds at visible wavelengths. It will consist of two Shack-Hartmann wavefront sensors (WFS) and two deformable mirrors (DM) plus a separate Tip/Tilt mirror. Both wavefront sensors will be situated in the pupil plane of the telescope. One determines the high order wavefront aberrations for the center of the field of view (FOV), the other measures only low order wavefront aberrations, but covers a large FOV in each subaperture. A 35 actuator bimorph mirror and a 37 actuator membrane mirror will correct the ground layer and the tropopause, respectively. For wavefront reconstruction, the mirror eigenmodes will be used. The system will have first light in the first quarter of 2003. Scientific operation is expected to start in April 2003 or July 2003.
We present the optical setup and wavefront reconstruction algorithms for the multi-conjugate adaptive optics (MCAO) system at the 70 cm German Vacuum Tower Telescope (VTT), Observatorio del Teide, Tenerife. The system is designed to increase the corrected field of view (FOV) from about 10 arcseconds to 30 arcseconds in the visible. It will consist of two Shack-Hartmann wavefront sensors (WFS) and two deformable mirrors (DMs). Both wavefront sensors will be situated in the pupil plane of the telescope. One determines the high order wavefront aberrations for the center of the FOV, the other measures only low order wavefront aberrations, but covers a large FOV in each subaperture. A 35 actuator bimorph mirror and a micro mirror will correct the ground layer and the tropopause, respectively. The system will have first light in early 2002. Scientific operation is expected to start in the second half of 2002.
We describe an adaptive optics system for the 1.5m diameter solar telescope GREGOR which is currently developed for the Teide Observatory on Tenerife. In a first development step, the AO will provide compensation of 77 modes of wavefront deformation, corresponding to the first 10 radial degrees of a Karhunen-Loeve decomposition of wavefront error. We estimate that such a performance will render GREGOR nearly diffraction limited at visible wavelengths in conditions which correspond to the best 25% of the seeing In Tenerife. The AO uses a Shack-Hartmann wavefront sensor which operates on fine structure anywhere on the solar disk. The required control bandwidth will be about 200 Hz. We show how such a system can be realized using existing technology. Substantial increases in performance in terms of corrected wavefront error and field requires significant technological advances, in particular in the field of large field high speed detectors.
Polarimetry is an important method to investigate the physics of the solar atmosphere. If the magnetic field strength is not strong enough to produce completely split Zeeman profiles the degree of polarization is a measure for the field strength. Measuring both the circular and linear polarization allows in principle the construction of the magnetic field vector including magnitude and direction. Unfortunately these highly desired measurements are in many cases affected by the instrument's optic itself. Especially telescopes which don't have a rotation symmetry with respect to their optical axis suffer from these problems. This is also the case with our German Vacuum Tower Telescope at Tenerife and this paper shall show the instrumental effects which are to be expected. One of the effects is crosstalk between linear and circular polarization. We show a method where this crosstalk can be considered as a tool and may be used--under certain assumptions--to derive the true size of magnetic elements which may cover only a fraction of the resolution element.