Showing papers on "Adaptive optics published in 2000"

Michelson Interferometry with the Keck I Telescope

Abstract: We report the —rst use of Michelson interferometry on the Keck I telescope for diUraction- limited imaging in the near-infrared JHKL bands. By using an aperture mask located close to the f/25 secondary, the 10 m Keck primary mirror was transformed into a separate-element, multiple-aperture interferometer. This has allowed diUraction-limited imaging of a large number of bright astrophysical targets, including the geometrically complex dust envelopes around a number of evolved stars. The suc- cessful restoration of these images, with dynamic ranges in excess of 200:1, highlights the signi—cant capabil- ities of sparse aperture imaging as compared with more conventional —lled-pupil speckle imaging for the class of bright targets considered here. In particular, the enhancement of the signal-to-noise ratio of the Fourier data, precipitated by the reduction in atmospheric noise, allows high-—delity imaging of complex sources with small numbers of short-exposure images relative to speckle. Multiepoch measurements con—rm the reliability of this imaging technique, and our whole data set provides a powerful demonstration of the capabilities of aperture-masking methods when utilized with the current generation of large-aperture tele- scopes. The relationship between these new results and recent advances in interferometry and adaptive optics is brie—y discussed.

Adaptive optics based on analog parallel stochastic optimization: analysis and experimental demonstration

Abstract: Wave-front distortion compensation using direct system performance metric optimization is studied both theoretically and experimentally. It is shown how different requirements for wave-front control can be incorporated, and how information from different wave-front sensor types can be fused, within a generalized gradient descent optimization paradigm. In our experiments a very-large-scale integration (VLSI) system implementing a simultaneous perturbation stochastic approximation optimization algorithm was applied for real-time adaptive control of multielement wave-front correctors. The custom-chip controller is used in two adaptive laser beam focusing systems, one with a 127-element liquid-crystal phase modulator and the other with beam steering and 37-control channel micromachined deformable mirrors. The submillisecond response time of the micromachined deformable mirror and the parallel nature of the analog VLSI control architecture provide for high-speed adaptive compensation of dynamical phase aberrations of a laser beam under conditions of strong intensity scintillations. Experimental results demonstrate improvement of laser beam quality at the receiver plane in the spectral band up to 60 Hz.

Introduction to Adaptive Optics

Abstract: A Long Time Ago, in a Laboratory Far, Far, Really Far, Far Away Adaptive Optics Systems - Optics is Our Middle Name Speaking the Language - a Few Definitions Atmospheric Turbulence - Bad Air... Bad, Bad Air Laser Guide Stars - a Beacon in the Wilderness Systems -Putting it All Together Wavefront Sensors - the Eyes Deformable Mirrors - the Hands Control Computers and Reconstructors - the Brains.

Smart microscope: an adaptive optics learning system for aberration correction in multiphoton confocal microscopy.

Abstract: Off-axis aberrations in a beam-scanning multiphoton confocal microscope are corrected with a deformable mirror. The optimal mirror shape for each pixel is determined by a genetic learning algorithm, in which the second-harmonic or two-photon fluorescence signal from a reference sample is maximized. The speed of the convergence is improved by use of a Zernike polynomial basis for the deformable mirror shape. This adaptive optical correction scheme is implemented in an all-reflective system by use of extremely short (10-fs) optical pulses, and it is shown that the scanning area of an f:1 off-axis parabola can be increased by nine times with this technique.

Adaptive-optics corrections available for the whole sky

Abstract: Adaptive-optics systems can in principle allow a telescope to achieve performance at its theoretical maximum (limited only by diffraction), by correcting in real time for the distortion of starlight by atmospheric turbulence1. For such a system installed on an 8-m-class telescope2,3, the spatial resolution and sensitivity could be up to 100 times better than conventional imaging4,5. Adaptive-optics corrections have hitherto been achieved only for regions of the sky within a few arcseconds of a bright reference source. But it has been proposed theoretically that by using multiple guide stars, the tomography of atmospheric turbulence could be probed and used to extend adaptive-optics corrections to the whole sky6,7. Here we report the experimental verification of such tomographic8 corrections, using three off-axis reference stars ∼15 arcsec from the central star. We used the observations of the off-axis stars to calculate the deformations of the wavefront of the central star, and then compare them with the real measured values. This tomographic approach is found to reduce variations in the wavefront by ∼92%. Our result demonstrates that a serious barrier to achieving diffraction-limited seeing over the whole sky has been removed.

Solar adaptive optics

Abstract: High resolution observations of the Sun are of key importance in understanding fundamental astrophysical processes. Adaptive optics (AO) is an important tool that allows solar astronomers to achieve diffraction limited observations from existing ground based telescopes. AO is also a key technology required for a future 4m-class Advanced Solar Telescope (AST) that the international community of solar astronomers is planning to build. The history of the development of solar AO is reviewed and results from recent successful demonstrations of solar AO systems are presented. The main difference between solar AO and night time AO is the different, and more elaborate wavefront sensing technique that has to be applied in order to measure wavefront aberrations using solar granulation as a target. Different approaches to this problem are discussed. Multi-conjugate AO has been proposed as a technique to achieve diffraction limited resolution over a field-of-view (FOV) significantly larger than the isoplanatic patch. The Sun is an ideal object for the development and application of MCAO.

A low cost adaptive optics system using a membrane mirror

Abstract: A low cost adaptive optics system constructed almost entirely of commercially available components is presented. The system uses a 37 actuator membrane mirror and operates at frame rates up to 800Hz using a single processor. Numerical modelling of the membrane mirror is used to optimize parameters of the system. The dynamic performance of the system is investigated in detail using a diffractive wavefront generator based on a ferroelectric spatial light modulator. This is used to produce wavefronts with time-varying aberrations. The ability of the system to correct for Kolmogorov turbulence with different strengths and effective wind speeds is measured experimentally using the wavefront generator.

Adaptive optics for 100-m-class telescopes: new challenges require new solutions

Abstract: For giant, 100 m-class, telescopes, a completely new class of problems arises. Trying to solve them adopting the techniques used for the classical 4 ... 10 m-class telescope systems is indeed a reductive approach. Because of the cone effect and of the difficulties in retrieving the tilt due to the use of LGSs, tomography and multiconjugation will play a central role in the development of these systems. We review the tomographic concept and we report about recent experiments to validate the concept using sky observations. The Field of View requirement is another crucial step in the design of the optical system of these telescopes and hence it needs to be attacked in a detailed and as wide as possible approach. The adoption of classical wavefront sensors looking to different stars is here overcome with wavefront sensors directly conjugated to different layers, with big advantages in term of intrinsic complication of the system, both from the optomechanical point of view (less complexity and saving of a huge amount of light) and from the computational point of view. The adoption of these new sensing techniques (that, gaining from the close loop situation, can be efficiently coupled to a number of very faint stars, whose complexity does not scale with the number of references but, rather, to the number of sensed layers) is here reviewed. This concept of multiple object wavefront sensing leads to an example of a system with a minimum number of independent adaptive optics loop, in which each layer represented in a wavefront sensor can be conjugated to a specifically conjugated deformable mirror.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Palomar adaptive optics project : status and performance

Abstract: We describe the current performance of the Palomar 200 inch (5 m) adaptive optics system, which in December of 1998 achieved its first high order (241 actuators) lock on a natural guide star. In the K band (2.2 micrometer), the system has achieved Strehl ratios as high as 50% in the presence of 1.0 arcsecond seeing (0.5 micrometer). Predictions of the system's performance based on the analysis of real-time wavefront sensor telemetry data and an analysis based on a fitted Kolmogorov atmospheric model are shown to both agree with the observed science image performance. Performance predictions for various seeing conditions are presented and an analysis of the error budget is used to show which subsystems limit the performance of the AO system under various atmospheric conditions.

Principles, limitations, and performance of multiconjugate adaptive optics

Abstract: Multi-Conjugate Adaptive Optics (MCAO) holds the promise of moderate to large adaptively compensated field of view with uniform image quality. This paper is a first effort to analyze the fundamental limitations of such systems, and that are mainly related to the finite number of deformable mirrors and guide stars. We demonstrate that the ultimate limitation is due to the vertical discretization of the correction. This effect becomes more severe quite rapidly with increasing compensated field of view or decreasing wavelength, but does not depend at first order on the telescope aperture. We also discuss limitations associated with the use of laser guide stars and ELT related issues.

Achromatic interfero coronagraphy I. Theoretical capabilities for ground-based observations

Abstract: We present a concept dedicated to the detection of faint companions or other morphological components in the neighbouring of a star by means of coronagraphy. Basically this method relies on destructive interferences so as to achieve extinction of the on-axis point-like source. In this regard the reported concept is a nulling interferometer designed for work with a single aperture. Two features are specic to our coronagraph, namely achromaticity and close-sensing. Achromaticity allows flexible choice of a working wavelength and of a large spectral bandwidth. Close-sensing provides the ability to explore around the central source signicantly closer than can be achieved by existing coronographs. Though our concept has been initially devised for use on a space-based instrument it is the goal of this paper to show by theoretical analysis that it can be ecient and powerful on ground-based large telescopes equipped with adaptive optics. This especially regards close-sensing capabilities at a level (better than diraction limit) un- reachable by other coronagraphs. The essential limitation regarding detection originates in residual wavefront distor- tions whose eects are described here using the formalism of adaptive optics. In this paper the principle, the generic set-up and the limitations are briefly recalled. Algebraic derivations re- garding the eect of atmospheric seeing and the use of adaptive optics are given. Theoretical expected detection capabilities for ground-based operation are derived, show- ing that detection of a companion fainter than the central star by 6 magnitudes with a Signal to Noise Ratio (SNR) of 5 appears to be a reasonable goal from raw data, with a 4-meter class telescope in rather ordinary conditions and with modest integration times. On-going progress in adap- tive optics, make it conceivable to reach magnitude dier- ences of 12 under similar conditions.

Isoplanatism in a multiconjugate adaptive optics system.

Abstract: Turbulence correction in a large field of view by use of an adaptive optics imaging system with several deformable mirrors (DM's) conjugated to various heights is considered. The residual phase variance is computed for an optimized linear algorithm in which a correction of each turbulent layer is achieved by applying a combination of suitably smoothed and scaled input phase screens to all DM's. Finite turbulence outer scale and finite spatial resolution of the DM's are taken into account. A general expression for the isoplanatic angle thetaM of a system with M mirrors is derived in the limiting case of infinitely large apertures and Kolmogorov turbulence. Like Fried's isoplanatic angle theta0,thetaM is a function only of the turbulence vertical profile, is scalable with wavelength, and is independent of the telescope diameter. Use of angle thetaM permits the gain in the field of view due to the increased number of DM's to be quantified and their optimal conjugate heights to be found. Calculations with real turbulence profiles show that with three DM's a gain of 7-10x is possible, giving the typical and best isoplanatic field-of-view radii of 16 and 30 arcseconds, respectively, at lambda = 0.5 microm. It is shown that in the actual systems the isoplanatic field will be somewhat larger than thetaM owing to the combined effects of finite aperture diameter, finite outer scale, and optimized wave-front spatial filtering. However, this additional gain is not dramatic; it is less than 1.5x for large-aperture telescopes.

Status of the VLT Nasmyth adaptive optics system (NAOS)

Abstract: NAOS is the adaptive optics system to be installed at one of the Nasmyth focus of the VLT. It was designed and manufactured by a French Consortium to provide compensated images to the high angular resolution IR spectro-imaging camera (CONICA) in the 1 to 5 micrometer spectral range. For bright sources, NAOS will achieve a Strehl ratio of 70% under average seeing conditions. It is equipped with a 185 actuator deformable mirror, a tip/tilt mirror and two wavefront sensors, one in the visible and one in the near IR. All the components of NAOS have been delivered and the integration phase is in progress since the beginning of 2000. After extensive tests and performance verifications in France, the system will be shipped to Chile by the end of 2000. The first light at the VLT is foreseen in the beginning of 2001.

Thermal Performance Enhancement of Adaptive Optics by Use of a Deformable Secondary Mirror

Abstract: An adaptive optics system is being built for the 6.5 m Multiple Mirror Telescope (MMT) conversion on Mount Hopkins for diffraction-limited observations in the near-infrared. At the heart of the system is a deformable secondary mirror which introduces corrections to the optical wavefront. By compensating these errors at the telescope's secondary, the system has been optimized for low thermal emissivity and high photon throughput. The scientific productivity of the facility will thereby be enhanced in comparison with a telescope equipped with more conventional adaptive optics. The Large Binocular Telescope under construction on Mount Graham will also use adaptive secondary mirrors. This paper explores the benefit to both facilities in terms of the integration time required to achieve a given signal-to-noise ratio. The gain is found to be substantial in the photometric bands K, L, M, and N.

Progress on Altair: The Gemini North Adaptive Optics System

Abstract: The Gemini Adaptive Optics System, (Altair), under construction at the National Research Council of Canada's Herzberg Institute of Astrophysics is unique among AO systems. Altair is designed with its deformable mirror (DM) conjugate to high altitude. We summarize construction progress. We then describe Altair in more detail. Both the Wavefront sensor foreoptics and control system are unconventional, because the guide star footprint on an altitude-conjugated DM moves as the guide star position varies. During a typical nodding sequence, where the telescope moves 10 arcseconds between exposures, this footprint moves by half an actuator and/or WFS lenslet. The advantages of altitude conjugation include increased isoplanatic patch size, which improves sky coverage, and improved uniformity of the corrected field. Altitude conjugation also reduces focal anisoplanatism with laser beacons. Although the initial installation of Altair will use natural guide stars, it will be fully ready to use a laser guide star (LGS). The infrastructure of Gemini observatory provides a variety of wavefront sensors and nested control loops that together permit some unique design concepts for Altair.

Scanning laser ophthalmoscope for selective therapeutic laser

Abstract: A combination of a scanning laser ophthalmoscope and external laser sources (52) is used for microphotocoagulation and photodynamic therapy, two examples of selective therapeutic laser. A linkage device incorporating a beamsplitter (56) and collimator-telescope (60) is adjusted to align the pivot point (16) of the scanning lasers (38, 40) and external laser source (52). A similar pivot point minimizes wavefront aberrations, enables precise focusing and registration of the therapeutic laser beam (52) on the retina without the risk of vignetting. One confocal detection pathway of the scanning laser ophthalmoscope images the retina. A second and synchronized detection pathway with a different barrier filter (48) is needed to draw the position and extent of the therapeutic laser spot on the retinal image, as an overlay (64). Advanced spatial modulation increases the selectivity of the therapeutic laser. In microphotocoagulation, an adaptive optics lens (318) is attached to the scanning laser ophthalmoscope, in proximity of the eye. It corrects the higher order optical aberrations of the eye optics, resulting in smaller and better focused applications. In photodynamic therapy, a spatial modulator (420) is placed within a collimator-telescope (60) of the therapeutic laser beam (52), customizing its shape as needed. A similar effect could be obtained by modulating a scanning laser source (38) of appropriate wavelength for photodynamic therapy.

New challenges for adaptive optics: extremely large telescopes

Abstract: ABSTRA C T The performance of an adaptive optics (AO) system on a 100-m diameter ground-based telescope working in the visible range of the spectrum is computed using an analytical approach. The target Strehl ratio of 60 per cent is achieved at 0.5mm with a limiting magnitude of the AO guide source near R magnitude , 10; at the cost of an extremely low sky coverage. To alleviate this problem, the concept of tomographic wavefront sensing in a wider field of view using either natural guide stars (NGS) or laser guide stars (LGS) is investigated. These methods use three or four reference sources and up to three deformable mirrors, which increase up to 8-fold the corrected field size (up to 60 arcsec at 0.5mm). Operation with multiple NGS is limited to the infrared (in the J band this approach yields a sky coverage of 50 per cent with a Strehl ratio of 0.2). The option of open-loop wavefront correction in the visible using several bright NGS is discussed. The LGS approach involves the use of a faintOR , 22U NGS for low-order correction, which results in a sky coverage of 40 per cent at the Galactic poles in the visible.

Wave front control systems based on modal liquid crystal lenses

Abstract: We describe two electro-optical systems for adaptive focusing of linearly polarized light. The aperture size is 5 mm and the focal length can be varied from 1 to 4 m for wavelengths from 0.663 to 0.85 μm. The first is a commercially available system including a PC compatible control unit and software, and an adaptive liquid crystal lens. The other is an experimental system consisting of a self-contained unit with an autonomous power supply and an adaptive lens. The safe operating limit in the visible region is 10 W/cm2 with a transmission of 70% without antireflection coating. The switching speed of focus variation from 2 to 1 m and from 1 to 2 m is 780 and 860 ms, respectively. The operating principles of the spherical adaptive lenses and their control units are described. Phase aberrations of the lenses were measured by a Zygo phase shifting interferometer, and the results are presented.

Using single-mode fibers to monitor fast Strehl ratio fluctuations - Application to a 3.6 m telescope corrected by adaptive optics

Abstract: The theory of starlight coupling into single-mode fibers is reviewed to show how i) the central obstruction in a telescope pupil deteriorates coupling efficiency much more than one would expect from the loss of collecting area, and ii) a single-mode fiber and a photometer can be used to monitor fast Strehl ratio fluctuations. This last point is illustrated with experimental data obtained at the 3.6 m La Silla telescope corrected with the ADONIS adaptive optics system. A 37× gain in coupling efficiency was demonstrated by turning on the adaptive optics system, but periodic fluctuations in the coupled signal revealed a vibration of the telescope tube that could not have been detected otherwise.

Adaptive optics: wave-front correction by use of adaptive filtering and control

Abstract: A class of adaptive-optics problems is described in which phase distortions caused by atmospheric turbulence are corrected by adaptive wave-front reconstruction with a deformable mirror, i.e., the control loop that drives the mirror adapts in real time to time-varying atmospheric conditions, as opposed to the linear time-invariant control loops used in conventional adaptive optics. The basic problem is posed as an adaptive disturbance-rejection problem with many channels. The solution given is an adaptive feedforward control loop built around a multichannel adaptive lattice filter. Simulation results are presented for a 1-m telescope with both one-layer and two-layer atmospheric turbulence profiles. These results demonstrate the significant improvement in imaging resolution produced by the adaptive control loop compared with a classical linear time-invariant control loop.

Adaptive wave-front correction by means of all-optical feedback interferometry.

Abstract: A novel adaptive wave-front correction system based on an all-optical feedback interferometer is described. In this system the two-dimensional output fringe intensity from a Mach-Zehnder interferometer with large radial shear is optically fed back to an optically addressed phase-only liquid-crystal spatial light modulator. Consequently, without a separate aberration-free reference wave, the modulator phase approximates the conjugate of the interferometer phase that is directly related to the phase of the input aberrated wave front, so this system is applicable in adaptive optics. We successfully achieved real-time correction of aberrated wave fronts: A diffraction pattern that was seriously distorted because of aberrations was transformed into a diffraction-limited spot immediately after the feedback loop was closed.

Laser guide star adaptive optics for astronomy

Abstract: Preface. List of Participants. 1. Optical Effects of a Atmospheric Turbulence J.C. Dainty. 2. Adaptive Optics with Laser Guide Stars: Basic Concepts and Limitations A. Quirrenbach. 3. The Physics of the Sodium Atom E.J. Kibblewhite. 4. The Design and Performance of Laser Systems for Generating Sodium Beacons E. Kibblewhite. 5. Laser Guide Star Operational Issues C.E. Max. 6. The Cone Effect R. Foy. 7. Laser Guide Star Advanced Concepts: Tilt Problem R. Raggazoni. 8. The Tilt Problem - Multiwavelength R. Foy. 9. Sky Doverage with Laser Guide Star Systems on 8m Telescopes M. Le Louarn. 10. Ground Based Astronomy with Adaptive Optics S.T. Ridgway. 11. Polarimetric Measurements and Deconvolution Techniques N. Ageorges. 12. Measuring Asteroids with Adaptive Optics J.C. Drummond. 13. The Environments of Young Stars T.P. Ray. 14. Distant (Radio) Galaxies: Probes of Galaxy Formation H. Rottgering. 15. Active Galaxies in the Local and Distant Universe C.S. Rola. Index.

Adaptive optics on large telescopes

Abstract: Observations withground based telescopes suffer from atmospheric turbulence.Independent of the telescope size the angular resolution inthe visible is equivalent to that of a telescope with adiameter of 10–20 cm. This effect is caused by the turbulentmixing of air with different temperatures in the atmosphere.Thus, the perfect plane wave from a star at infinity isaberrated before it enters the telescope. In the following,we will discuss the physical background of imaging throughturbulence, using Kolmogorov statistics, and the differenttechniques to sense and to correct the wave-front aberrationswith adaptive optics. The requirements for the control loop ofan adaptive optics system are discussed including formulas forthe limiting magnitude of the guide star as a function of thewave-front sensing method, of the quality of the wave-frontsensor camera, and of the degree of correction. Finally, ashort introduction to deformable mirror technology will begiven followed by the presentation of a new method to measureand to distinguish individual turbulent layers in order toincrease the isoplanatic angle.

System for beaming power from earth to a high altitude platform

Abstract: Power is transmitted to a high altitude platform by an array of diode pumped solid state lasers each operated at a single range of laser wavelengths outside of infrared and without using adaptive optics. Each laser produces a beam with a desired arrival spot size. An aircraft avoidance system uses a radar system for automatic control of the shutters of the lasers.

Numerical simulation of an adaptive optics system with laser propagation in the atmosphere

Abstract: A comprehensive model of laser propagation in the atmosphere with a complete adaptive optics (AO) system for phase compensation is presented, and a corresponding computer program is compiled. A direct wave-front gradient control method is used to reconstruct the wave-front phase. With the long-exposure Strehl ratio as the evaluation parameter, a numerical simulation of an AO system in a stationary state with the atmospheric propagation of a laser beam was conducted. It was found that for certain conditions the phase screen that describes turbulence in the atmosphere might not be isotropic. Numerical experiments show that the computational results in imaging of lenses by means of the fast Fourier transform (FFT) method agree well with those computed by means of an integration method. However, the computer time required for the FFT method is 1 order of magnitude less than that of the integration method. Phase tailoring of the calculated phase is presented as a means to solve the problem that variance of the calculated residual phase does not correspond to the correction effectiveness of an AO system. It is found for the first time to our knowledge that for a constant delay time of an AO system, when the lateral wind speed exceeds a threshold, the compensation effectiveness of an AO system is better than that of complete phase conjugation. This finding indicates that the better compensation capability of an AO system does not mean better correction effectiveness.

On the use of dual frequency nematic material for adaptive optics systems: first results of a closed-loop experiment.

Abstract: The use of liquid crystal devices for wavefront control has been suggested and implemented by several authors. In this paper we report some preliminary results on the use of Nematic based liquid crystal devices. Several experimental efforts have been carried out in the past few months. One of the main aims was to characterize a new device that uses dual frequency nematic material in a closed loop arrangement.

IRCAL: the infrared camera for adaptive optics at Lick Observatory

Abstract: We describe the design, characterization and performance of the IR Camera for Adaptive Optics at Lick (IRCAL). IRCAL is a 1-2.5 micron camera optimized for use with the LLNL Lick adaptive optics system on the Shane 3 m telescope. Using diamond-turned gold-coated optics, the camera provides high efficiency diffraction limited imaging throughout the near- IR. IRCAL incorporates optimizations for obtaining high dynamic range images afforded by adaptive optics, coronagraphic masks, and a cross-dispersed silicon grism for high resolution spectroscopy.

Zernike coefficients: are they really enough?

Abstract: Zernike aberration coefficients are routinely used in simulation exercises for lithographic printing and the discovery of Zernike values is considered strategic for many lithographic process engineers. Thanks to progress in actinic interferometry and resist based evaluation techniques, reliable estimates of Zernike component magnitudes are possible in many cases. It is expected that wavelength reductions from 248 nm and 193 nm to 157 nm along with continued use of aspheric elements in high NA designs will lead to an increase in the component of wavefront aberration that is not adequately characterized by a 36 term Zernike polynomial. Wavefront errors not well characterized by a conventional Zernike fit are variously termed mid- spatial frequency errors, lack of fit, residuals, flare, scatter etc. This paper explores the importance, characterization and analysis of these residual errors and attempts to clarify the boundaries between the various classes of wavefront error. We find that an accurate assessment an model of lens performance requires the inclusion of both residual wavefront errors and flare effects in addition to the customary 36 term Zernike expansion.

AMBER: the near-infrared focal instrument for the Very Large Telescope Interferometer

Abstract: AMBER is a focal instrument for the Very Large Telescope Interferometer working in the near infrared from 1.1 to 2.4 micrometers . It has been designed having in mind the General User of interferometric observations and the full range of his possible astrophysical programs. However the three programs used to define the key specifications have been the study of Young Stellar Objects, the study of Active Galactic Nuclei dust tori and broad line regions and the measure of masses and spectra of hot Extra Solar Planets. AMBER combines up to three beams produced by the VLTI 8 m Unit Telescopes equipped with Adaptive Optics and/or by the 1.8 m Auxiliary Telescopes. The fringes are dispersed with resolutions ranging from 35 to 10000. It is optimized for high accuracy single mode measurements of the absolute visibility, of the variation of the visibility and phase with wavelength (differential interferometry) and of phase closure relations with three telescopes. The instrument and its software are designed to allow a highly automated user friendly operation and an easy maintenance.