Showing papers by "Roberto Ragazzoni published in 2004"
TL;DR: In this paper, the authors derived the gas expansion law, diagnostics and ionic radial profiles, the distance and the central star parameters, the nebular photo-ionization model and the spatial recovery of the plasma structure and evolution.
Abstract: Tomographic and 3-Danalyses for extended, emission-line objects are applied to long-slit ESO NTT + EMMI high-resolution spectra of the intriguing planetary nebula NGC 7009, covered at twelve position angles. We derive the gas expansion law, the diagnostics and ionic radial profiles, the distance and the central star parameters, the nebular photo-ionization model and the spatial recovery of the plasma structure and evolution. The Saturn Nebula (distance ≃ 1.4 kpc, age ≃ 6000 yr, ionized mass ≃ 0.18 M ○. ) consists of several interconnected components, characterized by different morphology, physical conditions, excitation and kinematics. We identify four large-scale, mean-to-high excitation sub-systems (the internal shell, the main shell, the outer shell and the halo), and as many small-scale ones: the caps (strings of low-excitation knots within the outer shell), the ansae (polar, low-excitation, likely shocked layers), the streams (high-excitation polar regions connecting the main shell with the ansae), and an equatorial, medium-to-low excitation pseudo-ring within the outer shell. The internal shell, the main shell, the streams and the ansae expand at V exp : ≃ 4.0 x R km s -1 , the outer shell, the caps and the equatorial pseudo-ring at V exp ≃ 3.15 x R km s -1 , and the halo at V exp ≃ 10 km s -1 . We compare the radial distribution of the physical conditions and the line fluxes observed in the eight sub-systems with the theoretical profiles coming from the photo-ionization code CLOUDY, inferring that all the spectral characteristics of NGC 7009 are explainable in terms of photo-ionization by the central star, a hot (log T * ≃ 4.95) and luminous (log L * /L ○. ≃ 3.70) 0.60-0.61 M ○. post-AGB star in the hydrogen-shell nuclear burning phase. The 3-D shaping of the Saturn Nebula is discussed within an evolutionary scenario dominated by photo-ionization and supported by the fast stellar wind: it begins with the superwind ejection (first isotropic, then polar deficient), passes through the neutral, transition phase (lasting ≃3000 yr), the ionization start (occurred ≃2000 yr ago), and the full ionization of the main shell (≃1000 yr ago), at last reaching the present days: the whole nebula is optically thin to the UV stellar flux, except the caps (mean latitude condensations in the outer shell, shadowed by the main shell) and the ansae (supersonic ionization fronts along the major axis).
41 citations
TL;DR: LINC-NIRVANA as discussed by the authors is a 1-2.5 micron interferometric imaging instrument for the Large Binocular Telescope (LBT) with a field of view of ten arcseconds on a single HAWAII-2 detector array.
Abstract: We describe LINC-NIRVANA, a 1-2.5 micron interferometric imaging instrument for the Large Binocular Telescope. Operating in Fizeau beam combination mode, LINC-NIRVANA will deliver the sensitivity of a 12-meter telescope and the angular resolution of a 23-meter telescope. Unlike traditional interferometers, LINC-NIRVANA will be a true imaging device, with a field of view of ten arcseconds on a single HAWAII-2 detector array. LINC-NIRVANA employs a number of state-of-the-art technologies, including multi-conjugated adaptive optics (MCAO), innovative cooling systems, and complex software for instrument control and data analysis. We report on overall project progress and highlight some unique aspects of LINC-NIRVANA that should be of wider interest to the near-infrared instrument-building community.
31 citations
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TL;DR: In this article, the authors present the final design of MAD with a brief report about the status of the integration, which is based on a two deformable mirrors correction system and on two multi-reference wavefront sensors capable to observe simultaneously some preselected configurations of Natural Guide Stars.
Abstract: The European Southern Observatory together with external research Institutes is building a Multi-Conjugate Adaptive Optics Demonstrator (MAD) to perform wide field of view adaptive optics correction. The aim of MAD is to demonstrate on the sky the feasibility of the MCAO technique and to evaluate all the critical aspects in building such kind of instrument in the framework of both the 2nd generation VLT instrumentation and the 100-m Overwhelmingly Large Telescope (OWL).
The MAD module will be installed at one of the VLT unit telescope in Paranal to perform on-sky observations. MAD is based on a two deformable mirrors correction system and on two multi-reference wavefront sensors capable to observe simultaneously some pre-selected configurations of Natural Guide Stars. MAD is expected to correct up to 2 arcmin field of view in K band. MAD has just started the integration phase which will be followed up by a long period of testing. In this paper we present the final design of MAD with a brief report about the status of the integration.
27 citations
TL;DR: An update of this project, named PYRAMIR, which will have its first light in some months, and a description of the optical design is presented, which discusses issues like the image quality and chromatic effects due to band sensing.
Abstract: A new wavefront sensor based on the pyramid principle is being built at MPIA, with the objective of integration in the Calar Alto adaptive optics system ALFA. This sensor will work in the near-infrared wavelength range (J, H and K bands). We present here an update of this project, named PYRAMIR, which will have its first light in some months. Along with the description of the optical design, we discuss issues like the image quality and chromatic effects due to band sensing. We will show the characterization of the tested pyramidal components as well as refer to the difficulties found in the manufacturing process to meet our requirements. Most of the PYRAMIR instrument parts are kept inside a liquid nitrogen cooled vacuum dewar to reduce thermic radiation. The mechanical design of the cold parts is described here. To gain experience, a laboratory pyramid wavefront sensor was set up, with its optical design adapted to PYRAMIR. Different tests were already performed. The electronic and control systems were designed to integrate in the existing ALFA system. We give a description of the new components. An update on the future work is presented.
21 citations
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TL;DR: The Smart Fast Camera (SFC) as mentioned in this paper is a camera that can be placed on an aberrated Field of View, including those of slow focal ratios, to provide imaging at an equivalent focal ratio as low as F/1, with a size identical to the large focal ratio focal plane size.
Abstract: It is generally believed that very fast cameras imaging large Fields of View translate into huge optomechanics and mosaics of very large contiguous CCDs. It has already been suggested that seeing limited imaging cameras for telescopes whose diameters are larger than 20m are considered virtually impossible for a reasonable cost. We show here that, using existing technology and at a moderate price, one can build a Smart Fast Camera, a device that placed on aberrated Field of View, including those of slow focal ratios, is able to provide imaging at an equivalent focal ratio as low as F/1, with a size that is identical to the large focal ratio focal plane size.
The design allows for easy correction of aberrations over the Field of View. It has low weight and size with respect to any focal reducer or prime focus station of the same performance. It can be applied to existing 8m-class telescopes to provide a wide field fast focal plane or to achieve seeing-limited imaging on Extremely Large Telescopes. As it offers inherently fast read-out in a massive parallel mode, the SFC can be used as a pupil or focal plane camera for pupil-plane or Shack-Hartmann wavefront sensing for 30-100m class telescopes.
19 citations
TL;DR: This work proposes to string around the rim of a telescope a number of small telescopes that will add laser beams in the scattering medium to create a compact spot and could be adapted for ocular adaptive optics.
Abstract: Adaptive optics systems measure the wave front to be corrected by use of a reference source, a star, or a laser beacon. Such laser guide stars are a few kilometers long, and when observed near the edges of large telescopes they appear elongated. This limits their utility significantly. However, with more sophisticated launch optics their shape and length can be controlled. We propose to string around the rim of a telescope a number of small telescopes that will add laser beams in the scattering medium to create a compact spot. The method could also be adapted for ocular adaptive optics.
13 citations
TL;DR: In this article, a multi-conjugated adaptive optics (MCAO) with two 349 actuators deformable mirrors (DM), two 672 actuator deformable secondary mirrors and a total of 4 wavefront sensors (WFS) is used to increase sky coverage and achieve a medium Strehl-ratio over the 2 arcmin field of view.
Abstract: LINC-NIRVANA is an imaging interferometer for the Large Binocular Telescope (LBT) and will make use of multi-conjugated adaptive optics (MCAO) with two 349 actuators deformable mirrors (DM), two 672 actuator deformable secondary mirrors and a total of 4 wavefront sensors (WFS) by using 8 or 12 natural guide stars each. The goal of the MCAO is to increase sky coverage and achieve a medium Strehl-ratio over the 2 arcmin field of view. To test the concepts and prototypes, a laboratory setup of one MCAO arm is being built. We present the layout of the MCAO prototype, planned and accomplished tests, especially for the used Xinetics DMs, and a possible setup for a test on sky with an existing 8m class telescope.
13 citations
INAF1
TL;DR: In this paper, the optimal closed loop control law for multiconjugate adaptive optics (MCAO) is proposed based on a Kalman filter and a feedback control, which allows to take into account the wavefront sensing noise, the turbulence profil model, the Kolmogorov statistics and a temporal model of the turbulence.
Abstract: We first recall in this paper the optimal closed loop control law for multiconjugate adaptive optics [MCAO]. It is based on a Kalman filter and a feedback control. The prior model on which is based the Kalman filter is developped in a state-space representation and the differences in the model between Star Oriented [SO] MCAO and Layer Oriented [LO] MCAO are presented. This approach allows to take into account the wavefront sensing noise, the turbulence profil model, the Kolmogorov statistics and a temporal model of the turbulence. Simulation results are given in SO MCAO and the Kalman based approach is compared to the more standard Optimized Modal Gain Integrator [OMGI].
13 citations
TL;DR: The Prime Focus for the Large Binocular Telescope (PF-LBT) as discussed by the authors is a two-camera system with four 4kx2k CCDs and a six lenses corrector with an aspheric surface.
Abstract: The Prime Focus for the Large Binocular Telescope are a couple of Prime Focus stations each equipped with four 4kx2k CCDs and a six lenses corrector with an aspheric surface and the first lens as large as roughly 800mm in diameter. These cameras will cover almost half degree of Field of View on 8m-class telescopes with unprecedented velocity of F/1.4. The two units are optimized for the Red and Blue portions of the visible wavelength and additionally an extension to J and H bands is foreseen. An overview of the project, including the optomechanics, the cryogenics, the electronics, and the software is given along with a preliminary account of lessons learned and on how much the second unit, the Red one, the schedule of which is shifted with respect to the Blue one by several months, will take advantage from the experience gained in the Blue unit assembly and integration.
12 citations
INAF1
TL;DR: In this article, the alignment of the prime focus corrector with the primary mirror of the Large Binocular Telescope is described, a rather challenging activity due to the tight alignment tolerances and the size of the lenses.
Abstract: While this paper is written, the Blue channel of the double prime focus camera for the Large Binocular Telescope is being commissioned at the telescope. We report here on the optical alignment of the prime focus corrector, a rather challenging activity, due to the tight alignment tolerances and to the size of the lenses. Furthermore we describe the current plans about the alignment of the prime focus corrector with the primary mirror of the telescope, which is foreseen in the next few months.
8 citations
TL;DR: The Fringe and Flexure Tracking System (FFTS) as discussed by the authors is a fundamental component to ensure a complete and time-stable wavefront correction at the position of the science detector in order to allow for long integration times atinterferometric angular resolutions.
Abstract: LINC-NIRVANA is the interferometric near-infrared imaging camera for the Large Binocular Telescope (LBT).Operating at JHK bands LINC-NIRVANA will provide an unique and unprecedented combination of high angularresolution ( 9 milliarcseconds at 1.25 µm ), wide eld of view ( 100 arcseconds 2 at 1.25 µm ), and largecollecting area ( 100 m 2 ).One of the major contributions of the I. Physikalische Institut of the University of Cologne to this projectisthedevelopmentoftheFringeandFlexureTrackingSystem (FFTS). In close cooperation with the AdaptiveOptics systems of LINC-NIRVANA the FFTS is a fundamental component to ensure a complete and time-stable wavefront correction at the position of the science detector in order to allow for long integration times atinterferometric angular resolutions.Using a dedicated near-infrared det ector array at a combined focus close to the science detector, the Fringeand Flexure Tracking System analyses the interferometric point spread function (PSF) of a suitably brightreference source at frame rates of several hundred Hertz up to 1 kHz. By tting a parameterized theoreticalmodel PSF to the preprocessed image-data the FFTS determines the amount of pistonic phase dierence andthe amount of an angular misalignment between the wavefronts of the two optical paths of LINC-NIRVANA.For every exposure the correcting parameters are derived in real-time and transmitted to the respective controlelectronics, or the Adaptive Optics syst ems of the single-eye telescopes, which will adjust their optical elementsaccordingly.In this paper we present the opto-mechanical hardware design, the principle of operation of the softwarecontrol algorithms, and the results of rst numerical simulations and laboratory experiments of the performanceof this Fringe and Flexure Tracking System.Keywords: LBT, instrumentation, interferometry, fringe tracking, piston
07 Jul 2004
TL;DR: In this paper, a wavefront sensor is introduced taking advantage of the concept by the means of two optical devices, a reflecting rod and a mask, which can be used to detect pseudo infinity guide stars (PIGS).
Abstract: Since several problems of Laser Guide Stars, like conical anisoplanatism, perspective elongation, etc, scales with the telescope diameter, the use of artificial stars will become more difficult with apertures in the range of ELTs Problems with Laser Guide Stars are reviewed and a way is shown how to overcome most of these difficulties with the concept of Pseudo Infinity Guide Stars (PIGS) A new kind of wavefront sensor is introduced taking advantage of the concept by the means of two optical devices, a reflecting rod and a mask We explain this novel wavefront sensor, show results of a laboratory experiment, and conclude in further steps to apply the concept with full MCAO capability
07 Jul 2004
TL;DR: Adaptive Optics for Extremely Large Telescopes could need to be forzen, at conceptual level, within a few years as discussed by the authors, which requires to identify the directions of innovation which can have some chance to give improvement by a large factor.
Abstract: Adaptive Optics for Extremely Large Telescopes could need to be forzen, at conceptual level, within a few years. This requires to identify the directions of innovation which can have some chance to give improvement by a large factor. I try to outline some examples of such possible developments, in order to get an idea of how much margin can still be available for innovating concepts in this recently growing field.
TL;DR: In this article, a 2m-class telescope is proposed for the science case of short duration (10s or greater) microlensing events in the crowded central regions of Galactic Globular Clusters and nearby galaxies.
Abstract: Wide-Field imaging at visible wavelengths with seeing of the order of 0.1-0.2arcsec is believed to be possible from the high Antarctic plateau site of Dome-C by the removal of ground layer effects only. We present a proposal for a 2m-class telescope specifically designed for the science case of short duration (~10s or greater) microlensing events in the crowded central regions of Galactic Globular Clusters and nearby galaxies where the achievement of a spatial resolution of the order of a fraction of arcsec is essential.
The philosophy behind the telescope proposal is discussed in detail. It is emphasized that this is a project with a specific unique science goal in mind and not a large scale facility instrument. A preliminary design for the optics, ground layer removal using a deformable secondary and "static" wavefront sensor and telescope structure is presented. In particular, it is shown that substantial simplification in the design can be achieved by having a specific science goal in mind, so reducing the complexity and increasing reliability. Transport and logistics for the successful deployment and operation of the telescope at the Dome-C site are discussed.
TL;DR: The sky coverage problem in the Layer Oriented case is studied, using both numerical and analytical approaches, and a distribution of numerically simulated cases that allows computing the sky coverage with respect to a performance parameter as the Strehl Ratio and to the scientific field size is retrieved.
Abstract: One of the key-point for the future developments of the multiconjugate adaptive optics for the astronomy is the availability of the correction for a large fraction of the sky. The sky coverage represents one of the limits of the existing single reference adaptive optics system. Multiconjugate adaptive optics allows to overcome the limitations due to the small corrected field of view and the Layer Oriented approach, in particular by its Multiple Field of View version, increases the number of possible references using also very faint stars to guide the adaptive systems. In this paper we study the sky coverage problem in the Layer Oriented case, using both numerical and analytical approaches. Taking into account a star catalogue and a star luminosity distribution function we run a lot of numerical simulation sequences using the Layer Oriented Simulation Tool (LOST). Moreover we perform for several cases a detailed optimization procedure and a relative full simulation in order to achieve better performance for the considered system in those particular conditions. In this way we can retrieve a distribution of numerically simulated cases that allows computing the sky coverage with respect to a performance parameter as the Strehl Ratio and to the scientific field size.
TL;DR: In this paper, a pyramid wavefront sensor was used to add light from multiple natural guide stars to the Fizeau interferometer for the Large Binocular Telescope (LBT).
Abstract: Several multi-conjugate adaptive optics (MCAO) systems using the layer-oriented approach are under construction and will soon be tested at different facilities in several instruments. One of these instruments is LINC-NIRVANA, a Fizeau interferometer for the Large Binocular Telescope (LBT). This instrument uses a ground layer wavefront sensor (GWS) and a combined mid-high layer wavefront sensor (MHWS) with different fields of view (concept of multiple field of view), a 2-6 arcmin annular ring for the GWS and a 2 arcmin diameter central field of view for the MHWS. Both sensors are Pyramid wavefront sensors which optically co-add light from multiple natural guide stars.
The opto-mechanical problems concerning these sensors are related to the fast focal ratio of the beam on the pyramids coupled with the available pixelscale of detectors. This leads to very tight requirements on the moving systems (linear stages) for the star enlargers (SE) used to pick off the light of individual stars.
As there are 40 star enlargers in the overall system, additional efforts were put into the alignment system of the optics of the star enlargers and the reduction in size of the star enlargers to minimize the distance between available guide stars.
TL;DR: The LINC-NIRVANA is one of the few MCAO instruments in the world which will see first light and go into operation within the next few years as discussed by the authors.
Abstract: On the way to the Extremely Large Telescopes (ELT) the Large Binocular
Telescope (LBT) is an intermediate step. The two 8.4m mirrors create a masked aperture of 23m. LINC-NIRVANA is an instrument taking advantage of this opportunity. It will get, by means of Multi-Conjugated Adaptive Optics (MCAO), a moderate Strehl Ratio over a 2 arcmin field of view, which is used for Fizeau (imaging) interferometry in J,H and K. Several MCAO concepts, which are
proposed for ELTs, will be proven with this instrument. Studies of sub-systems are done in the laboratory and the option to test them on sky are kept open. We will show the implementation of the MCAO concepts and control aspects of the instrument and present the road map to the final installation at LBT. Major milestones of LINC-NIRVANA, like preliminary design review or final design review are already done or in preparation. LINC-NIRVANA is one of the
few MCAO instruments in the world which will see first light and go into operation within the next years.
07 Jul 2004
TL;DR: LINC-NIRVANA is a Fizeau interferometer which will be built for the Large Binocular Telescope (LBT) as discussed by the authors, which consists of two 84m mirrors on one mounting with a distance of 228m between the outer edges of the two mirrors.
Abstract: LINC-NIRVANA is a Fizeau interferometer which will be built for the Large Binocular Telescope (LBT) The LBT exists of two 84m mirrors on one mounting with a distance of 228m between the outer edges of the two mirrors The interferometric technique used in LINC-NIRVANA provides direct imaging with the resolution of a 23m telescope in one direction and 84m in the other The instrument uses multi-conjugated adaptive optics (MCAO) to increase the sky coverage and achieve the diffraction limit in J, H, K over a moderate Field of View (2 arcmin in diameter) During the preliminary design phase the team faced several problems similar to those for an instrument at a 23m telescope We will give an overview of the current design, explain problems related to 20m class telescopes and present solutions
07 Jul 2004
TL;DR: In this paper, the authors proposed a different approach to multi conjugate adaptive optics, in which pupil plane wavefront sensors (like the pyramid one) are conjugated to the same altitudes as the deformable mirrors.
Abstract: Layer Oriented represented in the last few years a new and promising aproach to solve the problems related to the limited field of view achieved by classical Adaptive Optics systems. It is basically a different approach to multi conjugate adaptive optics, in which pupil plane wavefront sensors (like the pyramid one) are conjugated to the same altitudes as the deformable mirrors. Each wavefront sensor is independently driving its conjugated deformable mirror thus simplifying strongly the complexity of the wavefront computers used to reconstruct the deformations and drive the mirror themselves, fact that can become very important in the case of extremely large telescopes where the complexity is a serious issue. The fact of using pupil plane wavefront sensors allow for optical co-addition of the light at the level of the detector thus increasing the SNR of the system and permitting the usage of faint stars, improving the efficiency of the wavefront sensor. Furthermore if coupled to the Pyramid wavefront sensor (because of its high sensitivity), this technique is actually peforming a very efficient usage of the light leading to the expectation that, even by using only natural guide stars, a good sky coverage can be achieved, above all in the case of giant telescopes. These are the main reasons for which in the last two years several projects decided to make MCAO systems based on the Layer Oriented technique. This is the case of MAD (an MCAO demonstrator that ESO is building with one wavefront sensing channel based on the Layer Oriented concept) and NIRVANA (an instrument for LBT). Few months ago we built and successfully tested a first prototype of a layer oriented wavefront sensor and experiments and demonstrations on the sky are foreseen even before the effective first light of the above mentioned instruments. The current situation of all these projects is presented, including the extensive laboratory testing and the on-going experiments on the sky.
TL;DR: In this paper, a wave front sensing concept was proposed to overcome the sky coverage problem with a laser guide star (LGS) generated in the sodium layer of the mesosphere at an height of approximately 90km-100km.
Abstract: The next generation ground based telescopes deploy their full potential in terms of resolution only with Adaptive Optics (AO). A limiting factor for such systems is the sky coverage with natural guide stars. A way to overcome this problem is a artificial star, i.e. laser guide star (LGS) generated in the sodium layer of the mesosphere at an height of approximately 90km-100km. Sensing the wave front of such a LGS, whose photons are collected by a next generation ground based telescope up to 100m pupil diameter leads to new problems. They are related to the finite distance of the altitude where the artificial star forms with respect to the telescope entrance pupil. We present a new wave front sensing concept to overcome this problem and we show first results of an open loop experiment done on sky. Measurements have been carried out November 2003 with the Rayleigh laser of the University of Durham at the WHT in La Palma as a result of collaboration between MPIA and the AO group of the University of Durham. The geometry of the LGS created in 4km altitude with respect to the 4m aperture of the WHT scales by a factor 1:25 with a sodium LGS at 100km and a telescope with 100m entrance pupil diameter.
TL;DR: In this paper, a 1:3 scale model of the LINC-NIRVANA interferometer is presented, which is used to test many aspects of the interferer before the final instrument is integrated.
Abstract: We present a 1:3 scale model of the LINC-NIRVANA interferometer. This
laboratory Fizeau, or image plane, interferometer allows us to test many aspects of LINC-NIRVANA before the final instrument is integrated. We have used this testbed interferometer to practice alignment procedures, verify the optical design, show that point spread functions with low (10\%) Strehl ratio can maintain high fringe contrast, and test the fringe tracking algorithm by running the interferometer in a closed piston loop.
TL;DR: This work will describe the construction of the wave front sensor of MAD5, and present the sensor performance showing the first open loop results.
Abstract: MAD5 is a Multi-Conjugate Adaptive Optics (MCAO) system conceived to demonstrate the feasibility of MCAO on the sky. The wave front sensor part is divided in two channels: a Shack-Hartmann sensor and a Layer Oriented sensor. We will describe the construction of the latter one. Assembly, integration and test of the instrument are the first steps for ESO acceptance, before integrating the Layer Oriented sensor with the other components of MAD. We will show qualitative and quantitative results of optical and mechanical tests: in particular we will describe the alignment of the references selection unit, constituted by sixteen motorized linear positioners and eight star enlargers, of the beam compressor and of the two re-imaging objectives, each one conjugated to a different altitude. Being the pyramid the core of this kind of wave front sensor, we will focus our attention on its construction difficulties and we will discuss all the optical tests made to choose the best ones to be installed on the wave front sensor. Finally we will present the sensor performance showing the first open loop results.
07 Jul 2004
TL;DR: In this paper, a conceptual layout for an active control of the wavefront sensor, in order to reach the best mechanical positioning of these star enlargers, is presented, and an algorithm to determine the effective pupils positions by simple movements and apply the requested displacement through commercially available piezoelectric actuators, shown in a preliminary opto-mechancial design of such wavefront sensors.
Abstract: Layer Oriented wavefront sensors can be made with a reasonable compact detector by the adoption of several stars enlargers, increasing only locally the focal ratio on the reference stars. The main opto-mechanical requirement in this kind of device is represented by the tolerances in tip and tilt of these star enlargers, which have to be moved over the Field Of View and aligned with the reference stars. A differential tip-tilt among the star enlargers leads to a mismatch between the different pupil images related to the reference stars. This misalignment eventually translates into a blurring of the measured wavefront, reducing the sensing quality. We describe a conceptual layout for an active control of the wavefront sensor, in order to reach the best mechanical positioning of these stars enlargers. In particular we discuss an algorithm to determine the effective pupils positions by simple movements and apply the requested displacement through commercially available piezoelectric actuators, shown in a preliminary opto-mechancial design of such wavefront sensor.
INAF1
TL;DR: In this article, the authors propose to use the superimposition of the light coming from several references at the level of the detector in order to increase the SNR and is using just the signal which is needed to drive loops indipendently tuned to different altitudes.
Abstract: In the framework of the Multi Conjugate Adaptive Optics technique several new ideas have been proposed in the last new years to improve the quality of the correction by using in the most possible efficient way the light coming from the references. The Layer Oriented approach, based on the usage of pupil plane wavefront sensors such as the pyramid, is using the superimposition of the light coming from several references at the level of the detector in order to increase the SNR and is using just the signal which is needed to drive loops indipendently tuned (in term of spatial and temporal sampling) to different altitudes. The Multiple Field of View technique proposes to increase the field of view of the detectors conjugated to altitudes close to the ground (where the pupil superimposition is high), thus increasing the probability to find suitable references and consequently the equivalent photon density on the metapupil.
The Multiple Resolution technique is instead based on the idea of somehow increasing the depth of focus of the detectors in order to maximize the volume of atmosphere sensed by each detector even by using large Field of Views.
Ground layer MCAO has also been proposed as a technique to accomplish only partial correction over a wide field of view and some on sky experiments are going to be exploited on the sky. From time to time there might be the impression that we arrived to a kind of a limit for the efficiency of the systems, considering that the light is limited by the FoV that cannot be increased indefinitely, but this might be a by product of the fact to look at the wavefront reconstruction in a linear fashion. In fact, it has been already shown in the past that it is possible to drive additional DMs by using the signal coming from detectors not conjugated to them, but this is accomplished by using a quadratic reconstruction. Furthermore, more recently, the idea of using the signal coming from an anular region surrounding the scientific field of view to improve the correction in the centre has also been suggested and again the signal has to be treated in a quadratic way. All these considerations suggest that there is still room for improvements at the expense of giving up on some conventional approaches to treat these problematics.
TL;DR: MEMORIS (MErcury Moderate Resolution Imaging System) is a wide angle camera (WAC) concept for the ESA mission BepiColombo as mentioned in this paper, which will obtain a map of Mercury in stereo mode allowing the determination of a digital elevation model with a panchromatic filter through two different channels.
TL;DR: In this paper, it was shown that one can build a 100m-class wavefront sensing with today existing components and that 100mscale wave front sensing of layers in the atmosphere is also possible with todayexisting technology.
Abstract: It is shown that one can build a 100m-class wavefront sensing with today existing components and that 100m-scale wavefront sensing of layers in the atmosphere is also possible with today existing technology
TL;DR: The LINC-NIRVANA is a Fizeau interferometer for the Large Binocular Telescope (LBT) doing imaging in the near infrared (J,H,K -band).
Abstract: LINC-NIRVANA is a Fizeau interferometer for the Large Binocular Telescope (LBT) doing imaging in the near infrared (J,H,K - band). Multi-conjugated adaptive optics is used to increase sky coverage and to get diffraction limited images over a 2 arcminute field of view. The control system consists of five independent loops, which are mediated through a master control. Due to the configuration, LINC-NIRVANA has no delay line like other interferometers. To remove residual atmospheric piston, the system must control both the primary and secondary mirrors, in addition to a third, dedicated piston mirror. This leads to a complex and interlocked control scheme and software. We will present parts of the instrument software design, which was developed in an object-oriented manner using UML. Several diagram types were used to structure the overall system and to evaluate the needs and interfaces of each sub-system to each other.
TL;DR: The Adaptive Optics System of the Galileo Telescope (AdOpt@TNG) is the only adaptive optics system mounted on a telescope which uses a pyramid wavefront snesor and it has already shown on sky its potentiality.
Abstract: The Adaptive Optics System of the Galileo Telescope (AdOpt@TNG) is the only adaptive optics system mounted on a telescope which uses a pyramid wavefront snesor and it has already shown on sky its potentiality. Recently AdOpt@TNG has undergone deep changes at the level of its higher orders control system. The CCD and the Real Time Computer (RTC) have been substituted as a whole. Instead of the VME based RTC, due to its frequent breakdowns, a dual pentium processor PC with Real-Time-Linux has been chosen. The WFS CCD, that feeds the images to the RTC, was changed to an off-the-shelf camera system from SciMeasure with an EEV39 80x80 pixels as detector. While the APD based Tip/Tilt loop has shown the quality on the sky at the TNG site and the ability of TNG to take advantage of this quality, up to the diffraction limit, the High-Order system has been fully re-developed and the performance of the closed loop is under evaluation to offer the system with the best performance to the astronomical community.
07 Jul 2004
TL;DR: In this article, the optical design of the layer-oriented wavefront sensors for two 8m class telescopes was presented, where a combination of fast optics and "stars enlargers" was used to shrink the pupil image in a way to fit the available detectors.
Abstract: We present the optical design of the layer-oriented wavefront sensors for two 8m class telescopes. By a combination of fast optics and "stars enlargers" it is possible to shrink the pupil image in a way to fit the available detectors. These concepts are then extended to the design of a wavefront sensor for a 100 m class telescope.
07 Jul 2004
TL;DR: In this paper, the laser creating the artificial beacon is broken up into many weak independent laser, sent from scattered locations up to the periphery of a large telescope to reduce significantly spot elongation in adaptive optics systems.
Abstract: It is possible to reduce significantly spot elongation in adaptive optics systems, if the laser creating the artificial beacon is broken up into many weak independent lasers, sent from scattered locations up to the periphery of a large telescope