The purpose of this paper is to report on new adaptive optics (AO) developments at the W. M. Keck Observatory since the 2002 SPIE meeting. These developments include continued improvements to the natural guide star (NGS) facilities, first light for our laser guide star (LGS) system and the commencement of several new Keck AO initiatives.

Three sets of sky tests have been conducted at the Starfire Optical Range with a continuous-wave, single-frequency, 20-W laser in preparation for a 50-W facility-class laser. Brightness measurements were made of the sodium guidestar produced with and without adaptive optics (AO) correction to the outgoing laser beam when it was either linearly or circularly polarized. Correcting for the transmission of our V filter at the sodium wavelength, a circularly polarized laser beam of 12 W out the telescope produced a guidestar of V=7.1 (1015 ph/s/cm² at the top of the telescope). In general, a circularly polarized beam produces a guidestar between 75 and 100% brighter than a linearly polarized beam, indicating a significant degree of optical pumping of the sodium D2-line magnetic sublevels. However, guidestars produced with beams launched with tip-tilt correction only were 11% brighter than with beams launched with full AO correction. From deconvolved images of the guidestar taken with the 3.5-m telescope, the smallest spot, produced from a beam with 8.5 W of power out the telescope, circular polarization, and launched closed loop, had a Gaussian FWHM of 0.85 arcsec, or 38 cm at an altitude of 92 km. This corresponds to a peak Gaussian intensity of 3.8 mW/cm².

The Multiple Mirror Telescope (MMT) adaptive optics system (MMT-AO) has been operated in a campaign mode for the last two years. In total seven runs, each lasting about two weeks, have been carried out. During these observational runs a large amount of data have been collected. These data allow us to draw some preliminary conclusions about the overall system performances. In this paper we discuss in detail the achieved performances of the MMT-AO system which is equipped with the first adaptive secondary ever developed. The performances are examined both in terms of number of corrected modes and control bandwidth achieved. We also discuss our attempts to improve the system calibration. This is done by modulating the internal slope offsets while the system is operating in closed loop on the sky.

Solar adaptive optics has become an indispensable tool at ground based solar telescopes. Over the last few years several solar adaptive optics systems have been deployed at major ground based solar telescopes. These systems enable diffraction limited observations of the sun for a significant fraction of the available observing time at these telescopes. New ground breaking scientific results have been achieved with solar adaptive optics. This paper summarizes the recent progress in the field of solar adaptive optics.

In April and August ’03 two MACAO-VLTI curvature AO systems were installed on the VLT telescopes unit 2 and 3 in Paranal (Chile). These are 60 element systems using a 150mm bimorph deformable mirror and 60 APD’s as WFS detectors. Valuable integration & commissioning experience has been gained during these 2 missions. Several tests have been performed in order to evaluate system performance on the sky. The systems have proven to be extremely robust, performing in a stable fashion in extreme seeing condition (seeing up to 3”). Strehl ratio of 0.65 and residual tilt smaller than 10 mas have been obtained on the sky in 0.8” seeing condition. Weak guide source performance is also excellent with a strehl of 0.26 on a V~16 magnitude star. Several functionalities have been successfully tested including: chopping, off-axis guiding, atmospheric refraction compensation etc. The AO system can be used in a totally automatic fashion with a small overhead: the AO loop can be closed on the target less than 60 sec after star acquisition by the telescope. It includes reading the seeing value given by the site monitor, evaluate the guide star magnitude (cycling through neutral density filters) setting the close-loop AO parameters (system gain and vibrating membrane mirror stroke) including calculation of the command-matrix. The last 2 systems will be installed in August ’04 and in the course of 2005.

We report here the preliminary results obtained with the multi-conjugate adaptive optics (MCAO) system at the Dunn Solar Telescope (DST/NSO MCAO) and the optical setup and performances are presented in more details in Moretto et al. in this proceeding. This system relies on the tomography technique, in which three WFS are used, each of them coupled to extended images of the Sun’s granulation and/or sunspots, to retrieve a 3D measurement of the turbulent volume in order to command the two DMs. We used a 5x5 subaperture Shack-Hartmann with cross correlation applied on three selected guiding regions - 18" wide- within the 1.25' full FOV. We also report on the estimation of turbulence distribution and the future MCAO performances based on a separate tomographic wavefront sensing experiment using the Dunn Solar Telescope adaptive optics system. In addition, we obtained estimates of the turbulence distribution. The results from this article provides an important step forward for building a full solar multi-conjugate adaptive optics system for the Dunn Solar Telescope and in the long term for the future 4 meter ATST telescope.

In this paper we evaluate the on-sky performance of Altair, the facility adaptive optics instrument at the Gemini North telescope. We describe the method for doing this on-sky evaluation, which includes: 1) the choice of suitable stellar fields for PSF observations that must cover a range of guide star magnitudes and angular separations from the guide star; 2) the observation strategy and data reduction pipeline; and 3) the PSF database from which the performance results are queried. The database stores observatory system parameters and performance observations such as FWHM, Strehl, encircled energy, wave front sensor flux, as well as coherence length (r_o) and outer scale (L_o) of the turbulence measured in closed loop and therefore coincident with the focal plane observations of the telescope. From the database we derive 20 to 24% Noll efficiency of the system and an estimated distribution of effective turbulence height above the summit to be 3.3 ± 0.6km. The performance evaluation strategy used on Altair is quite general and could be used for other adaptive optics systems.

NAOMI is the AO system of the 4.2-m William Herschel Telescope on La Palma. It delivers near-diffraction-limited images in the IR, and a significantly improved PSF at optical wavelengths. The science cameras currently comprise an IR imager (INGRID), an optical integral-field spectrograph (OASIS) and a coronagraph which may be placed in the light path to either instrument. 19 science programmes were observed during 2002-3. Observing overheads are small, with as much as 60% of the night spent integrating on science targets. In late 2004 this year, the WFS will be equipped with a low-noise L3 CCD, giving a gain of a factor of 2 in S:N for faint guide stars. A Rayleigh laser guide star is under development, with first light expected summer 2006, providing a unique facility: AO-corrected optical integral-field spectroscopy anywhere on the northern sky.

The UnISIS adaptive optics system is now completed and ready for science observations. We describe the experience we have gained in building and using the system, and we give a preview of one new science goal: the use of Gaussian aperture pupil masks for high-contrast imaging of companion objects near bright stars. A key aspect of the UnISIS design is the simultaneous use of two wavefront sensors, one for natural stars and the other for the laser guide star. We demonstrate the performance of this calibration system with results from on-the-bench tests. We describe several practical aspects of observing at Mt. Wilson including our ability to predict the nights of best seeing with weather data available on-line. We also show how the laser guide star return signal is enhanced by observing at large zenith angles and compare this to Rayleigh scattering models.

We present the status of the 1st generation of adaptive optics systems in operation and in construction at ESO. We introduce the 2nd generation of AO facilities planned to be developed in the coming years for the VLT and describe the corresponding enabling technology R&D program. The concept of an Adaptive facility with multi-LGS and a Deformable Secondary at one the VLT Unit Telescope is introduced. Status and roadmap of ESO simulation tools and preliminary concepts for OWL Adaptive Optics as well as preliminary R&D plan are given.

The Natural Guide Star (NGS) Adaptive Optics System at the MMT Telescope (MMTAO) on Mt. Hopkins in Southern Arizona is the first in the world to use the secondary mirror as the correcting deformable mirror. Its 2.0 mm thin shell mirror, whose shape is controlled by 336 voice coil actuators, allows for nearly maximum throughput of light into the science camera. With several more deformable secondary mirrors coming online in the next few years, the lessons learned building, characterizing and operating the MMT Adaptive Optic System has proven to be quite valuable. These lessons will be discussed as well as future plans for the MMTAO System.

High resolution spectroscopy made an important step ahead 10 years ago, leading for example to the discovery of numerous exoplanets. But the IR did not benefit from this improvement until very recently. CRIRES will provide a dramatic improvement in the 1-5 micron region in this field. Adaptive optics will allow us increasing both flux and angular resolution on its spectra. This paper describes the adaptive optics of CRIRES, its main limitations, its main components, the principle of its calibration with an overview of the methods used and the very first results obtained since it is installed in the laboratory.

The paper describes the single conjugate AO system called WLBT to be mounted at LBT in late summer 2004. The WLBT is part of the Acquisition, Guiding & Wavefront sensing unit (AGW) attached to the front bent Gregorian foci derotator. The two key features of this system are the use of a pyramid wavefront sensor with variable sampling between 30x30 and 5x5 sub apertures plus the use of an adaptive secondary mirror having 672 actuators as wavefront corrector. The AO system is mainly working as atmospheric disturbance correction system in the near infrared (J,H and K band). However due to the large number of actuators and sub apertures, it can obtain good performance even in R and I band. The paper reports about development and integration of the system final unit in the lab. Then some initial tests aimed to do a system characterization are reported. The results we obtained are used to give an estimation of the performance that the system can reach at the telescope in terms of limiting magnitude.

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.

In this article, we present the VLT second generation instruments and we summarize the concept and capabilities of the Very Large Telescope (VLT) Adaptive Optics (AO) Facility. This Facility, composed mainly of a deformable secondary mirror and four laser guide stars (LGSs), aims at providing an adaptive optics infrastructure to feed multiple instruments. These instruments can range from wide or narrow field visible light correction (for example MUSE, X-Shooter) to wide field infra-red correction (Hawk-I, possibly K-MOS) and it could also provide a high Strehl mid-infrared system. In this article we analyze the performance of this AO facility in these various modes of operation.

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.

We describe SPLASH (Sky Projected Laser Array Shack-Hartmann) which is a method of laser guide star (LGS) wavefront sensing with reduced focal anisoplanatism (FA). We present the results of a semi-theoretical analysis and a semi-geometrical simulation of SPLASH, allowing a direct comparison between SPLASH and a conventional laser guide star system. We show that SPLASH is significantly less susceptible to focal anisoplanatism than a conventional LGS.

We report in this paper on the current activities of the Laser Guide Star group at ESO. We are building the Laser Guide Star Facility on the VLT UT4, we are pushing new technologies in view of multiple LGS and future ELT LGS-AO systems. We are studying new LGS propagation/sensing schemes, to get rid of the LGS cone effect. We are also fostering in member states countries the development of fast sensors to deal with pulsed lasers atmospheric layer sensing.

The PARSEC laser system is designed for the VLT Laser Guide Star Facility to deliver a high power cw laser beam at 589nm, in order to create an artificial guide star in the mesospheric Sodium layer. The laser consists of a resonant, dye based power amplifier which is injection seeded with 589nm, single frequency radiation from a master oscillator. We report on the performance of the system both during the European Acceptance tests, and that which has been achieved in the laboratory. The maximum power we have obtained amounts to 20W cw laser light in a single mode and a single frequency at 589nm. With a beam quality of M² of 1.05-1.15 and a long term stability without manual intervention, the laser suits all the demands for operation at the VLT.

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.

Coherent Technologies, Inc. (CTI) is developing the first commercial solid-state sodium beacon laser guidestar (LGS): a critical step towards addressing the need of the astronomy adaptive optics (AO) community for a robust turn-key commercial LGS that can be upgraded for different observatory facilities and for different AO formats - including multi-conjugate AO (MCAO) and future extra-large telescopes. The LGS that is currently being developed will be a 14 W single beacon system to be installed on the center section of the Gemini North telescope in Fall 2004. This paper describes the Gemini North LGS requirements, the design of the laser with design trades against other LGS architectures; the functionality of the automated remote laser control system; latest size, weight, power, and performance data; and the current status of the program.

We report on the development of a 50-W, continuous-wave, sodium wavelength guidestar excitation source for installation on the azimuth gimbal structure of the 3.5-m telescope at the Starfire Optical Range. The laser is an all solid-state design employing two diode-pumped Nd:YAG sources operating at 1064 and 1319 nm that are combined to generate 589-nm radiation using a lithium triborate non-linear crystal. Key features of the system include single-frequency, injection-locked high-power oscillators, a doubly resonant sum frequency generator cavity, a short-term 10 kHz wide 589 nm spectrum, excellent beam quality and power stability, and turn-key operation using computer control and diagnostics. The laser beam is projected from the side of the 3.5-m telescope. A novel elevation beam dither approach is employed to determine range to the centroid of the guidestar formed in the column of mesospheric sodium and maintain focus of the wave front sensor.

A demonstration of tomographic wavefront sensing has been designed, fabricated, and tested. The last of the initial testing of the dynamic refocus system at the 61" telescope on Mt. Bigelow, Arizona is presented, along with the first results from the system after its transfer to the 6.5 m MMT on Mt. Hopkins, Arizona. This system consists of a laser beam projector, and a wavefront sensor at the telescope's Cassegrain focus. The projector transmits 5 pulsed 532 nm beams in a regular pentagon of 2 arcminutes diameter from behind the telescope's secondary mirror that in good seeing can yield sub-arcsecond beacons over a 20-30 km altitude range. The wavefront sensor incorporates a dynamic refocus unit to track each returning laser pulse, and a multiple laser beacon Shack-Hartmann wavefront sensor using a novel substitute for the traditional lenslet array. A natural guide star wavefront sensor was also fielded to collect ground-truth data to compare with wavefronts reconstructed from the laser wavefront sensor measurements. All of the subsystems were shown to work, but bad weather ended the testing before the final data could be collected.

For applications like direct imaging detections of Exo-Planets from the ground e.g. in the CHEOPS project, extreme adaptive optics (XAO) systems using DMs with > 1000 actuators and correction frequencies of ~2kHz are proposed to be used in combination with coronographic devices. If the XAO and science channel work at the same wavelength it is a natural idea to combine the coronograph with the XAO's beam splitter (BS) to make use of the light that would otherwise just be lost. However, the location of the BS in the focal plane and the severe field limitation of the AO by a small (~0.3'') aperture in the focal plane imposes a spatial filtering on the wavefront sensor signal. In this paper, we examine the effect of the spatial filter on the "AO control radius" and the Strehl ratio provided by the system in a semi-analytical way, numerical simulations for various wavefront sensor types and a laboratory verification experiment.

Optimization of a Shack-Hartmann based WFS is proposed for XAO systems. Both aliasing effects and noise propagation issues is investigated in order to optimize the WFS device. In particular a new estimator of the spot position is proposed and characterized both analytically and using end-to-end simulations. Analytical expressions of the slope measurement errors is derived and the gain brought by our new Weighted Center of Gravity estimator is quantified.

The new L3 Technology CCDs from E2V combine sub-electron read noise with high pixel rates. This makes them ideal candidates for wavefront sensing. ING's NAOMI adaptive optics instrument is currently limited by the readout noise of its wavefront sensor CCDs. Upgrading to L3 detectors has the potential to give a large increase in performance; simulations suggest a 2 magnitude improvement to the guide star limit. At ING we have explored the behaviour of various L3 devices in applications ranging from fast photometry, fast spectroscopy through to wavefront sensing. The investigations have been done using our own cryogenic cameras containing L3 devices coupled to an SDSU controller. An integral Peltier packaged CCD60 has also been purchased specifically for the WFS upgrade. This paper describes the progress we have made to date on the L3 wavefront sensor upgrade and our future plans for its use with a Rayleigh laser beacon.

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.

We present the development of silicon monolithic arrays of 60 photon-counters (SPADA, Single-Photon Avalanche Diode Array) for the visible. The SPADA system is suitable for state-of-the-art Adaptive Optics operations and Fast Transient image acquisitions, at quite a fraction of the current cost of imaging arrays. The fabricated solid-state photon counters are rugged, easy to be integrated in the optical system. They are free from readout noise and provide very fast frame-rates (>10kHz, for visible corrections) and nanosecond electronic gating (for ranging the up-going laser beam). The detection head has been integrated into an optomechanical system suitable for alignment and focusing in available astrophysics telescopes. The detection electronics includes an integrated Active Quenching Circuits for each pixel of the array. The real-time data-processing board is implemented into FPGA and DSP and is configurable for dealing with different applications: the extraction of the curvature wavefront for AO applications, and the acquisition and processing of two-dimensional images with fast frame rate. A remote host computer controls all the SPADA blocks and uploads the processed information and images. We report the optical and electrical characterization of the detectors and the associated electronics.

The Shack-Hartmann wavefront sensor operates by subdividing the complex field in the aperture plane of the telescope with a lenslet array and forming low resolution images of the object. An alternative wavefront sensing scheme can be derived from placing a lenslet array at the focal plane of the aperture and forming low resolution images of the aperture. This arrangement can be viewed as the generalisation of the pyramid sensor and enables direct comparisons of the pyramid sensor with the Shack-Hartmann sensor. In particular, in this paper the performance of the reconstructor of the two sensors is investigated. Simulation results demonstrate that the lenslet array at the focal plane has equivalent performance to the Shack-Hartmann sensor in open loop when no modulation is applied to the lenslet array. However, when the array is modulated in a manner akin to the pyramid sensor, subdivision at the focal plane provides a significantly better wavefront estimate than the Shack-Hartmann sensor.

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

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.

Current and future large telescopes depend critically on laser guide star adaptive optics (LGS AO) to achieve their scientific goals. However, there are still relatively few scientific results reported from existing LGS AO systems. We present some of the first science results from the Lick Observatory sodium beacon LGS AO system. We achieve high sensitivity to light scattered in the circumstellar enviroment of Herbig Ae/Be stars on scales of 100-200 AU by coupling the LGS AO system to a near-infrared (J,H,K_s bands) dual channel imaging polarimeter. We describe the design, implementation, and performance of this instrument. The dominant noise source near bright stars in AO images is a "seeing halo" of uncorrected speckles, and since these speckles are unpolarized, dual-channel polarimetry achieves a significant contrast gain. Our observations reveal a wide range of morphologies, including bipolar nebulosities with and without outflow-evacuated cavities and disk-mediated interaction among members of a binary. These data suggest that the evolutionary picture developed for the lower-mass T Tauri stars is also relevant to the Herbig Ae/Be stars, and demonstrate the ability of LGS AO systems to enhance the scientific capabilities of even modest sized telescopes.

In this paper we describe the operational strategy and performance of the Keck Observatory laser guidestar adaptive optics system, and showcase some early science verification images and results. Being the first laser guidestar system on an 8-10 m class telescope, the Keck laser guidestar adaptive optics system serves as a testbed for observing techniques and control algorithms. We highlight the techniques used for controlling the telescope focus and wavefront sensor reference centroids, and a wavefront reconstructor optimized for use with an elongated guidestar. We also present the current error budget and performance of the system on tip-tilt stars to magnitude R=17. The capability of the system to perform astronomical observations is finally demonstrated through multi-wavelength imaging of the Egg proto-planetary nebula (CRL 2688).

Sky coverage is an important item for a large number of techniques using stars as a reference, for example as guide stars for Adaptive Optics or for phase referencing in Interferometry. Models of the stellar distribution within our galaxy allow for reasonable estimates of the sky coverage under certain conditions, but these models do not give the detailed description that can only be obtained using observations. The newest generation star catalogues, like the USNO-B1.0 catalog in the visible wavelength band and the 2MASS catalog in the near-IR enable the exact determination of the sky coverage for a given requirement and location on the sky. Based on the above two catalogs the sky coverage as a function of parameters like limiting magnitude, number of guide stars and color was determined as a function of the location. In the context of the Multi Unit Spectroscopic Explorer (MUSE), a second generation instrument for the VLT which is currently being developed, the sky coverages for a number of potential targets--both progenitors of normal nearby galaxies at very high redshift, as found in deep fields like HDF-South and FORS deep field as well as nearby normal, starburst and interacting galaxies--were determined as illustrating examples.

Since the discovery of Dactyl orbiting around Ida by the Galileo spacecraft in 1993, over twenty-five binary asteroid systems have been discovered using radar, direct imaging and Adaptive Optics observations. Asteroidal moon discoveries dramatically increased with the advent of this last technique on ground based telescopes. Our group focuses on the search and study of double asteroids in the main-belt, in the Trojan population and beyond Neptune's orbit. We have been using several of the AO systems available (Lick-3m, Palomar-5m, VLT-8m, Keck-10m) and related techniques such as Appulse and Laser Guide Star observations to broaden the sample of asteroids observed from the main-belt out to the Kuiper Belt. We will present a quality comparison between various techniques and different AO systems with NGS and will detail our first successful observations with the Lick LGS system. Precise orbital elements of the secondary can be determined by multiple observations spanning large periods of time (several months). Our group developed a method to predict the ephemeris of a secondary companion. Without any assumptions, this method, tested successfully on 22 Kalliope and 121 Hermione binary systems, leads to the direct determination of important physical parameters of the targets, such as their mass and the interior structure, as well as gives direct insights on their formation processes that may be otherwise only be speculated on from spacecraft mission flybys.

The Natural Guide Star Adaptive Optics (NGS AO) system for the MMT Observatory is currently the only AO system in the world that uses a deformable secondary mirror to provide wavefront correction. This approach has unique advantages in terms of optical simplicity, high throughput and low emissivity. Here we present selected scientific results from the past year and a half of operation. Research with the AO system ranges from small scale structure around planetary nebulae, low mass stellar systems in the near IR, through to nulling interferometry in the mid infra-red.

As adaptive optics (AO) matures, it becomes possible to envision AO systems oriented towards specific important scientific goals rather than general-purpose systems. One such goal for the next decade is the direct imaging detection of extrasolar planets. An "extreme" adaptive optics (ExAO) system optimized for extrasolar planet detection will have very high actuator counts and rapid update rates - designed for observations of bright stars - and will require exquisite internal calibration at the nanometer level. In addition to extrasolar planet detection, such a system will be capable of characterizing dust disks around young or mature stars, outflows from evolved stars, and high Strehl ratio imaging even at visible wavelengths. The NSF Center for Adaptive Optics has carried out a detailed conceptual design study for such an instrument, dubbed the eXtreme Adaptive Optics Planet Imager or XAOPI. XAOPI is a 4096-actuator AO system, notionally for the Keck telescope, capable of achieving contrast ratios >10⁷ at angular separations of 0.2-1". ExAO system performance analysis is quite different than conventional AO systems - the spatial and temporal frequency content of wavefront error sources is as critical as their magnitude. We present here an overview of the XAOPI project, and an error budget highlighting the key areas determining achievable contrast. The most challenging requirement is for residual static errors to be less than 2 nm over the controlled range of spatial frequencies. If this can be achieved, direct imaging of extrasolar planets will be feasible within this decade.

The nascent field of planet detection has yielded a host of extra-solar planet detections. To date, these detections have been the result of indirect techniques: the planet is inferred by precisely measuring its effect on the host star. Direct observation of extra-solar planets remains a challenging yet compelling goal. In this vein, the Center for Adaptive Optics has proposed a ground-based, high-actuator density extreme AO system (XAOPI), for a large (~10 m) telescope whose ultimate goal is to directly evidence a specific class of these objects: young and massive planets. Detailed system wave-front error budgets suggest that this system is a feasible, if not an ambitious, proposition. One key element in this error budget is the calibration and maintenance of the science camera wave front with respect to the wave-front sensor which currently has an allowable contribution of ~ 5 nanometers rms. This talk first summarizes the current status of calibration on existing ground-based AO systems, the magnitude of this effect in the system error budget and current techniques for mitigation. Subsequently, we will explore the nature of this calibration error term, it’s source in the non-commonality between the science camera and wave front sensor, and the effect of the temporal evolution of non-commonality. Finally, we will describe preliminary plans for sensing and controlling this error term. The sensing techniques include phase retrieval, phase contrast and external metrology. To conclude, a calibration scenario that meets the stringent requirement for XAOPI will be discussed.

The proposed Giant Magellan Telescope (GMT) has a number of features that are well-suited to the task of imaging extrasolar planets in nearby star systems. The principal aid to this task is the large clear aperture segments which are relatively easy to apodize. This paper considers the methods currently envisaged to be of practical use for the task. In addition to star and planet fluxes, exoplanet imaging is dependent on aperture, throughput, bandwidth, beamwidth (FWHM), Strehl ratio (SR), and halo structure. Adaptive optics systems increase the SR, simultaneously dropping the residual scattered halo. This reveals the diffracted halo, which now becomes the limiting factor. Apodization reduces the diffracted halo, but at a cost in terms of throughput and a corresponding increase in photon noise. Since the best known ideal apodizations also have very low throughputs, they are not the best choices for ground-based exoplanet imaging. In addition, the ultra-low diffracted halos from these apodizations provide no benefit below the residual scattered halo, which is not helped by apodization. We consider instead a family of apodizations that have sufficiently dark diffracted halos, while retaining relatively high throughputs. One form of apodization can be applied to the GMT pupil using replicated apodization of individual segments, providing a low-halo survey mode that is high throughput and matched to the AO system. Since the reduced halo from the apodized segments only allows high-contrast detection to within a few λ/D_segment of the star, the single segment methods are limited by the segment size. We also consider the potential for apodizing the full aperture for high contrast at a few times λ/D_full through the use of an applied phase pattern, using either the adaptive secondary or a separate phase mask. We conclude that the phase mask method offers the best advantage for S/N since it does not lose light like the apodization schemes. However, it does have a restricted azimuthal search area, requiring multiple exposures to complete a survey. It appears to be the clearly best method for examining the exoplanet once discovered. It should be possible to apply offsets to the GMT's adaptive secondary to achieve constrasts of 10^-5 at 2xFWHM (27 mas at 1.65 μm, 80 mas at 5 μm) and 10^-6 at 3xFWHM (42 mas at 1.65 μm, 200 mas at 5 μm).

We discuss data reduction techniques and results from the Simultaneous Differential Imager (SDI) implemented at the VLT (Lenzen et al. 2004a) and the MMT. SDI uses a quad filter to take images simultaneously at 3 wavelengths surrounding the 1.62 μm methane bandhead found in the spectrum of cool brown dwarfs and gas giants. By performing a difference of images in these filters, speckle noise from the primary can be attenuated by a factor of >10². Non-trivial data reduction tools are necessary to pipeline the simultaneous differential imaging. Here we discuss a custom algorithm implemented in IDL to perform this reduction. The script performs basic data reduction tasks but also precisely aligns images taken in each of the filters using a custom shift and subtract routine. In our commissioning runs at the VLT and MMT, we achieved contrasts up to a factor of 45000 (ΔH=11.7) at a separation of 0.6" from the primary star. With this degree of attenuation, we should be able to image a 2-4 Jupiter mass planet at 5 AU around a 30 Myr star at 10 pc. We believe that our SDI images are the highest contrast astronomical images ever made from ground or space.

In PSFs obtained by AO systems, a cloud of speckles is surrounding the central diffraction core. These speckles don't average in time, and are extremely difficult to calibrate by the observation of a reference star. This "speckle noise" is setting the detection limit of faint companions around bright stars far above the photon noise. Speckles are coherent with the central diffraction core of the PSF, while a faint companion is not. By inducing interferences between the speckle cloud and a reference wave extracted from the central core of the PSF, it is possible to take advantage of this fundamental difference to identify and subtract the speckles. A time-variable phase delay is introduced in the reference wave in order to rapidly modulate the intensity of the speckles. The amplitude of this modulation leads to an accurate measure of the speckle intensity, which can then be subtracted to the image. This technique, which is compatible with spectroscopy, allows efficient detection of companions about 1000 times fainter than the speckles, and is especially attractive for exoplanet searches. The same technique can also be used on interferometers.

A end-to-end model of an Extreme Adaptive Optics system developed is the framework of the project VLT-PF is presented. The different components are exposed with their specificities. Several AO and XAO issues are discussed like scintillation, vibration and calibration effects among others. A full simulation of an XAO system coupled to a coronagraph and designed to detect faint companion in the vicinity of a bright star is shown.

This paper presents a series of studies of single conjugate adaptive optics systems that use numerical simulation to investigate aspects of system performance not addressed by traditional statistical metrics. These studies include investigations of temporal control loop dynamics and quantitative comparisons of system performance using different types of reconstructors.

We observe that a multi-conjugate adaptive optics (MCAO) system produces rapid fluctuations of irradiance of a few percent in the compensated focal plane when observing an extended target, such as the solar surface. Such fluctuations are absent in the uncompensated focal plane. The fluctuations are apparently correlated with the local curvature of deformable mirror in the plane conjugated to the high altitude turbulence layer. They can be explained by the field dependent change of effective focal length introduced by a high altitude turbulence layer, which is related to image distortion. Using a simple geometric model of the MCAO system, we are able to reproduce the observed irradiance effects. We propose to introduce a slightly undersized aperture stop at the location of the nominal exit pupil in order to remove the fluctuations in the compensated field.

The limit case of an infinite aperture adaptive optics (AO) system eliminates the modeling complications associated with aperture edge effects, and thereby enables the application of simplified methods for system performance evaluation in the spatial frequency domain. We review prior work in this field and describe a new approach that enables a wider range of error sources and AO options to be evaluated with a reduced number of approximations. These errors and AO options include: Fitting error and spatial aliasing for a Shack-Hartmann wavefront sensor (WFS) and one particular deformable mirror influence function; WFS noise; servo lag for a continuous temporal filter function; anisoplanatism in either a single evaluation direction or averaged over an extended field of view; piston removal within a finite aperture; minimum variance and modal wavefront reconstruction algorithms; and multi-conjugate AO. Laser guidestars, however, are excluded. A wide range of classical results for the independent effects of individual error sources can be immediately derived from this integrated model. Performance estimates for more complex problems involving the full range of first-order AO error sources are in good agreement with the results produced by more detailed Monte Carlo simulations.

We present recent developments of the CAOS "system", an IDL-based Problem Solving Environment (PSE) whose original aim was to define and simulate as realistically as possible the behavior of a generic adaptive optics (AO) system, from the atmospheric propagation of light, to the sensing of the wave-front aberratoins and the correction through a deformable mirror. The different developments made through the last 7 years result in a very versatile numerical tool complete of a global graphical interface (the CAOS Application Builder), and different specialized scientific packages: the original one designed for AO system simulations (the Software Package CAOS), an image reconstruction package with interferometric capabilities (the Software Package AIRY), and a more recent one being built and dedicated to multiconjugate AO (the Software Package MAOS). We present the status of the whole CAOS "system"/PSE, together with the most recent developments, including parallelization strategy considerations, examples of application, and plans for the next future.

In this paper, we summarize the analysis made on various Adaptive Optics (AO) modes (including Shack-Hartmann (SH) and Pyramid Wavefront Sensors (PWS)) for the OverWhelmingly Large telescope (OWL). We will show some early results of the performance to be expected with a first generation AO system, working in the infrared. Several telescope diameters were considered to see the variations as a function of telescope diameter. This is also compatible with the concept of "grow a telescope" where the telescope diameter of OWL grows from 60m to 100m as a function of time. In a first phase, to simplify the problem, the effects of the central obstruction were neglected. However, for the Shack-Hartmann (SH) simulations, additional simulations were carried out with a simulated OWL pupil, including segmentation errors. We show some early results for a ground-layer correction system, working with three natural guide stars (NGSs) and a single deformable mirror (DM). An MCAO system based on 2 DMs, 3 NGSs is also investigated. For the last two systems, our results are found to be in very good agreement with Cibola, an analytical AO modeling tool. We show that some outer scale of turbulence effects improve slightly the correction quality when going from a telescope diameter of 10m to 100m.

This paper contains a review of sparse matrix methods for open-loop wavefront estimation in astronomical adaptive optics systems with a large number of degrees of freedom. We address shortcomings of existing sparse methods for multiconjugate adaptive optics and propose some alternative approaches. We also review certain closed-loop control schemes, dubbed pseudo open-loop control (POLC), that make use of open-loop linear algebra, and we propose an extension of POLC that makes use of knowledge of atmospheric dynamics to carry out predictive estimation in closed loop.

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].

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.

In this paper we present a solution to the MCAO reconstruction problem using multiple laser guide stars and show that it can be interpreted as a form of back-projection tomography. It is shown that a key intermediate step is to determine a minimum-variance estimate of the index variations over the atmospheric volume. We follow the idea of Tokovinin and Viard [JOSA-A, April 2001] in initially formulating the problem in the Fourier domain; we then extend the interpretation to the spatial domain. The former results were limited to the case of infinite aperture and plane wave beacons, and the statistically optimal wavefront solution was given for a single science direction. The new approach is more general and interpretable as tomographic back-projections, which gives rise to algorithms for the finite aperture, cone (laser) beams, and wide-science-field cases. A fortuitous consequence of this analysis is that a "fast" algorithm suitable for real-time implementation has become evident. The reconstruction requires only filtering and the inversion of small (dimension = number of guidestars) matrices. In simulations, we compare results with those of a spatial domain least-square matrix-inversion method.

This paper describes the current control system of the multi-conjugate adaptive optics (MCAO) test bench system that is being developed at the University of Victoria, BC, Canada. The design and analysis of a control system for an AO system employing a Micro-Electro-Mechanical-System (MEMS) based deformable mirror and a PI tilt mirror is presented. This paper focuses on modal control of one deformable mirror and a tilt mirror with a Shack-Hartmann wave front sensor. Diagrams of how all the components work together as a control system are given. Bandwidth measurements for a single delay integrator controller and for a matched delay integrator are presented. Analysis shows that matching the delays of the integrator to the delays of the optical feedback loop provides considerable improvement in bandwidth.

The Gemini North adaptive optics system Altair utilises five cooperative CPU's to perform all the associated real-time tasks. One, the reconstructor (RTC), manages all of the highest speed hard real-time duties. As well as the core, computationally intensive, wavefront reconstruction, this processor implements a number of algorithms providing control system support services. These include: the quad-cell centroid gain estimation, determination and subtraction of invisible modes on the deformable mirror, and the blending of tip, tilt and focus from the on instrument wavefront sensors (which exist on all facility Gemini instruments). These associated support tasks are critically important to ensure that the system always runs with an optimal bandwidth and produce stable images with no artefacts such as a waffle pattern or residual non-common path errors. We present the original algorithm that we have developed for the centroid gain estimate and discuss how it is efficiently and conveniently implemented on the hard real-time processor.

ESO now operates several AO systems in the Paranal observatory. Most of them are the outcome of different and independent efforts resulting in different and incompatible systems with all the problems of maintaining and evolving them. At the same time, industry is now proposing powerful embedded computers and new standard technologies that enable the construction of massive real time parallel computers, with a technology roadmap that looks extremely promising. The ESO AO Platform initiative aims at taking this unique opportunity of gathering all the experience accumulated so far in building and operating AO system and the recent advances offered by the industry to define and build a standard hardware and software platform able to run every AO system of the near future of the VLT with an eye towards OWL. We review the key technologies that enable the design of a common AO-RTC and we discuss the main choices of the AO Platform initiative.

While the first MultiConjugate Adaptive Optics (MCAO) experimental set-ups are presently under construction, a growing attention is paid to the control loop. This is indeed a key element in the optimization process, especially for MCAO systems. Different approaches have been proposed in recent articles for astronomical applications: simple integrator, Optimized Modal Gain Integrator and Kalman filtering. We study here Kalman filtering, which seems a very promising solution. We have already proposed and simulated in simple cases a formalized adaptation of Kalman filtering to Adaptive Optics (AO) and MCAO. We wish now to characterize for the first time the frequential properties of this Kalman filter and to refine it so as to improve its robustness and performance, for instance in the presence of static aberrations and vibrations. Comparisons with classical controllers are proposed. Aliasing reduction could also be considered. In the near future, Kalman filter performance and robustness should be tested for realistic AO and MCAO configurations on a simulator and an experimental set-up.

An Adaptive Optics (AO) system for astronomy is analysed from a control point of view. The focus is put on the temporal error. The AO controller is identified as a feedback regulator system, operating in closed-loop with the aim of rejecting wavefront disturbances. Limitations on the performance of feedback regulator systems are discussed. The concept of optimal control is proposed to minimise the temporal error. The issue of closed-loop feedback controller design is made transparent by using the principle of Internal Model Control. The central issue in reducing the temporal wavefront is the design of a feedforward prediction filter. In three separate tests - a numerical simulation example, measured data from an AO test bench and open-loop telescope data - the advantage of optimal control over the common approach of integral control is demonstrated. Optimal control of the temporal error yields a smaller temporal error, enables a longer integration time in the wavefront sensor, or the use of fainter natural guide stars.

We present the concept of an instrument for the monitoring of the optical turbulence in the first 300 meters above the ground with an altitude resolution of 10 meters approximately. The method is based on a modified version of the generalized scidar. It could be implemented with the use of a 40-cm telescope, a 1376x1040 pixels CCD detector with low readout noise at 20 frames per second, a fast commercial personal computer and a colimating optics. The ideal light source is a bright double star with an angular separation of 180". The principal difference from a conventional generalized scidar is that the scintillation images produced by each star would be fully separated on the detector, whereas in a generalized scidar, the images overlap over a certain region. The image processing consists of selecting on the detector two subframes containing each the scintillation image of one of the stellar component, recenter each image on the corresponding subframe (to correct for telescope missguiding and shaking), and compute the spatial correlation of the two subframes. This procedure is to be repeated several thousand times and the output is the mean correlation. The data reduction would be very similar to that of the generalized scidar, which consists of the inversion of a Fredholm integral equation. This method is particularly interesting to study the turbulence above locations that are a few hundred meters below a given site summit.

The statistics of vertical structure of the turbulence affect the complexity of the design and implementation of Multi-Conjugate Adaptive Optics (MCAO) systems. The operation of these systems could be optimized if the stability of the layers were such as to permit to fix the deformable mirrors (DMs) at specific heights. Moreover, it is desirable to know the effects on the placement of the DMs and the gain of the isoplanatic angle in terms of site characterization. From the turbulence profiles measured with the G-SCIDAR technique we have analyzed the statistics of the heights of the DMs and the resulting isoplanatic angles. These results are based on the data from a long ongoing campaign at Roque de los Muchachos Observatory (La Palma) and Teide Observatory (Tenerife) with the highest statistical coverage to date. We have used two ideal MCAO systems, consisting of two and three DMs, and, from a specific comparison in simultaneous measurements over two nights, we show the evolution of the position of DMs and isoplanatic angles in both sites, which can sporadically reach values greater than 60" in 500 nm. We also study the effects of the stability of the conjugate planes on the improvements in the isoplanatic angles.

We report on the development of a prototype portable monitor for profiling of the altitude and velocity of atmospheric optical turbulence. The instrument is based on the SLODAR Shack-Hartmann wave-front sensing technique, applied to a portable telescope and employing an electron-multiplication (EM) CCD camera as the wave-front sensor detector. Constructed for ESO by the astronomical instrumentation group at the University of Durham, the main applications of the monitor will be in support of the ESO multi-conjugate adaptive optics demonstrator (MAD) project, and for site characterization surveys for future extremely large telescopes. The monitor can profile the whole atmosphere or can be optimized for profiling of low altitude (0-1km) turbulence, with a maximum altitude resolution of approximately 150m. First tests of the system have been carried out at the La Palma observatory.

The laser guide star adaptive optics (AO) system for Subaru Telescope is presented. The system will be installed at the IR Nasmyth platform, whereas the current AO system with 36 elements is operating at the Cassegrain focus. The new AO system has a 188 element wavefront curvature sensor with photon counting APD modules which is the largest control element curvature sensor system ever. The system will have 4-10 W solid state sum-frequency laser to generate a laser guide star. The laser launching telescope with 50 cm aperture will be installed at behind the secondary mirror. The laser unit will be installed on the third floor of the dome and the laser beam will be transferred to the laser launching telescope using single mode photonic crystal fiber cable. The field of view of the optics is 2.7 arcmin to maximize the probability to find tilt guide stars for laser guide star operation. The expected Strehl ratio as raw AO performance is 0.46 at H-band under 0.60" seeing with 12 th mag guide star, and 0.71 for 8 th mag stars. New wavefront modulation technique, dual stroke membrane mirror control, is developed to reduce the tilt error which is more dominant for curvature sensor AO system. The superb contrast imaging capability will be expected as natural guide star system. The first light as the natural guide star system is planned in March 2006, the laser first light will be expected in March 2007.

Here are presented the basis of an analytical development whose purpose is to give arguments for the evaluation of wavefront sensing concepts for Ground Layer Adaptive Optics. Simple hypothesis make possible the derivation of analytical expressions for the phase measurement error and reveal consequent differences between Star Oriented and Layer Oriented concepts. Influence of key parameters such as guide star statistics or strength of the turbulence in altitude are then studied. In the Layer Oriented case, necessity of reducing the guide stars flux dispersion to achieve a uniform correction in the field of interest is demonstrated.

The adaptive optics instrument for the SOAR 4.1-m telescope will improve the spatial resolution by 2-3 times at visible wavelengths, over a field of 3 arcmin, by sensing and correcting low-altitude turbulence selectively. We will use a Rayleigh laser guide star to accomplish this. We present the laser guide star design with predictions of system performance based on real turbulence statistics and telescope properties, sky coverage and some opto-mechanical aspects of the AO module. Various design trade-offs are discussed.

The scientific return on adaptive optics on large telescopes has generated a new vocabulary of different adaptive optics (AO) modalities. Multiobject AO (MOAO), multiconjugate AO (MCAO), ground-layer AO (GLAO), and extreme contrast AO (ExAO) each require complex new extensions in functional requirements beyond the experience gained with systems operational on large telescopes today. Because of this potential for increased complexity, a more formal requirements development process is recommended. We describe a methodology for requirements definition under consideration and summarize the current scientific prioritization of TMT AO capabilities.

An experimental Ground Layer Adaptive Optics system utilizing a low-altitude Rayleigh Laser Guide Star is presented. This demonstrator is designed for the GHRIL Nasmyth platform of the 4.2m William Herschel Telescope, where it uses a low-altitude (~4km) focused-spot 523nm Rayleigh-scatter beacon, launched from behind the secondary mirror using an independent beam launch telescope. A novel range-gate is used to select the LGS return altitude for wavefront sensing, whilst wavefront correction uses a 97-actuator continuous phase sheet deformable mirror and separate tip-tilt mirror. The performance can be monitored on-axis and off-axis. These and other aspects of the demonstration system are described in detail, including optical design, laser launch technique, laboratory performance, and a preliminary assessment of potential on-sky performance.

Optical-quality microelectromechanical deformable mirrors (DMs) and spatial light modulators (SLMs) are described. With such mirrors, the shape of the reflective surface can be modified dynamically to control an optical wavefront. A principal application is to compensate for aberrations and thereby improve image resolution in telescopes or microscopes: a process known as adaptive optics. μDMs are an enabling component for adaptive optics. Over several years, researchers at Boston University and Boston Micromachines Corporation have developed manufacturing processes that allow production of continuous and segmented deformable mirrors. We have produced mirror arrays with up to 22,500 actuators, 3.5μm of useful stroke, tens of picometer position repeatability, >98% reflectivity, and flatness better than 15nm RMS. Challenges to manufacturing optical quality micromachined mirrors in particular have been addressed: reducing surface roughness, increasing reflectivity, and eliminating post-release curvature in the mirror. These silicon based deformable mirrors can modulate spatial and temporal features of an optical wavefront, and have applications in imaging, beam-forming, and optical communication systems. New developments in DM design are discussed, and manufacturing approaches to microamachined DM and SLM production are presented, and designs that will permit scaling to millions of actuators are introduced.

With the future growing size of telescopes, new, high-resolution, affordable wavefront corrector technology with low power dissipation is needed. A new adaptive deformable mirror concept is presented, to meet such requirements. The adaptive mirror consists of a thin (30-50 μm), highly reflective, deformable membrane. An actuator grid with thousands of actuators is designed which push and pull at the membrane’s surface, free from pinning and piston effects. The membrane and the actuator grid are supported by an optimized light and stiff honeycomb sandwich structure. This mechanically stable and thermally insensitive support structure provides a stiff reference plane for the actuators. The design is extendable up to several hundreds of mm's. Low-voltage electro-magnetic actuators have been designed. These highly linear actuators can provide a stroke of 15 micrometers. The design allows for a stroke difference between adjacent actuators larger than 1 micron. The actuator grid has a layer-based design; these layers extend over a large numbers of actuators. The current actuator design allows for actuator pitches of 3 mm or more. Actuation is free from play, friction and mechanical hysteresis and therefore has a high positioning resolution and is highly repeatable. The lowest mechanical resonance frequency is in the range of kHz so a high control bandwidth can be achieved. The power dissipation in the actuator grid is in the order of milliwatts per actuator. Because of this low power dissipation active cooling is not required. A first prototype is currently being developed. Prototypes will be developed with increasing number of actuators.

The trend towards ever larger telescopes and more advanced adaptive optics systems such as multi-conjugate adaptive optics is driving the need for deformable mirrors with a large number of low cost actuators. Other applications require strokes larger than those readily available from conventional mirrors. Magnetically deformable liquid mirrors are a potential solution to both these problems. Depositing a thin silver colloid known as a metal liquid-like film (MELLF) on the ferrofluid surface solves the problem of low reflectivity of pure ferrofluids. This combination provides a liquid optical surface that can be precisely shaped in a magnetic field. We have demonstrated a reflective coating that is stable for more than 30 days with a reflectivity of 50% in the near infrared. Additional experiments indicate that MELLF coatings can provide near infrared reflectivity values in excess of 80%. We also report on recent response time measurements of liquid deformable mirrors. We have demonstrated liquid mirror actuators with slew rates of 800 μm/s, corresponding to an actuator bandwidth of approximately 40 Hz and 80 Hz for strokes of 10 μm and 5 μm respectively.

In the frame of the Large Binocular Telescope (LBT) adaptive secondary project, we developed a new dedicated electronics that controls the thin shell by means of 672 force actuators and capacitive sensor, while performing also the Real Time Reconstructor (RTR) computations. Within the adaptive optics system, the Slope Computer is also implemented using the same electronics, directly interfaced to the wavefront sensor CCD output by means of built-in fast parallel I/O channels. The system design has been tailored to balance the computational power, in the range of hundreds of Gigaflops, with an effective and time-deterministic real-time communication scheme. Diagnostic and maintenance are performed through an additional, fully independent communication line. Modularity, flexibility and remote in-system reconfigurability make this compact electronic suitable for real time adaptive optics control systems within a wide range of size and complexity, up to several thousands of actuators. In this paper we describe the general hardware and software architecture and the application results of this electronics within the LBT first light adaptive optics system.

We present here results using two novel adaptive optic elements, an electro-static membrane mirror built by OKO Technologies, and a dual frequency multi-segment nematic liquid crystal built by Meadowlark Optics. These devices have the advantage of low cost, low power consumption, and compact size. The total cost for these adaptive optics elements is hundreds of dollars per actuator as compared to a cost of thousands of dollars per actuator for conventional adaptive optics. Field experiments were performed on the Air Force Research Laboratory 3.67 meter telescope on Maui, Hawaii, with the aperture stopped down to 1.15 meters. It is believed that this is the first ever experimental demonstration of these two devices for adaptive correction of images of satellites. Recently, the control electronics for the liquid crystal device were rebuilt and we were able to increase the closed loop bandwidth from 40 to 80 Hz.

A study of the scintillation effects on the PSF halo of the high-contrast imaging instrument (CHEOPS) for direct exo-planet detection from the ground is presented. The fundamental goal of our analysis is to quantify the perturbations induced by the amplitude (scintillation) variations compared to those induced by the phase variations of a perturbed wavefront. Simulations of amplitude and phase screens are obtained for different seeing conditions and for a wavefront propagating at different zenith angles. For all cases a set of simulations of the PSFs in the ideal mirror-limited case (perfect AO-system) and an estimation of the detection limit Δm vs. angular separation obtained with and without scintillation are presented. The whole study is made in I-band (λ = 0.9 μm) i.e. the centered wavelength of the CHEOPS polarimetric imager. A maximum loss of contrast (obtained with and without scintillation) of ~ 25% over a FOV of 5 arcsec is found in the speckle noise-limited regime and of ~ 18% in the photon noise-limited regime. Results are discussed and conditions in which the scintillation effects cannot be neglected are investigated.

In this communication we study the utility and limitations of ground based coronagraphy with adaptive optics (AO). In very high AO correction regimes, residual speckles are pinned on the diffraction rings of the Airy pattern. It can be shown that these speckles are due to small defaults of the wavefront, amplified by the coherent part of the wave. Their statistics can be described by a modified Rice distribution, under reasonable physical assumptions. Using properties of the Moment Generating Function (MGF), simple expressions are obtained for the variances of the noise at high flux and at photon counting levels. We discuss the relative importance of speckle and photon noise and present conclusions on the limits of coronagraphy for the detection of an exoplanet. The total variance can be partitioned into two contributions: one that can be suppressed by a coronagraph and one that cannot, and different regimes can be identified. These results enable analysis of when a coronagraph can defeat the noise variance, and they provide a criterion for effectiveness of such instruments.

Strehl ratio is the most commonly used metric for adaptive optics (AO) performance. It is also the most misused metric. Every Strehl ratio measurement algorithm has subtle differences that result in different measured values. This creates problems when comparing different measurements of the same AO system and even more problems when trying to compare results from different systems. To determine how much the various algorithm difference actually impacted the measured values, we created a series of simulated point spread functions (PSF). The simulated PSFs were then sent around to the various members of the project who then measured the Strehl ratio. The measurements were done blindly, with no knowledge of the true Strehl ratio. We then compared the various measurements to the truth values. Each measurement cycle turned up impacts which were further investigated in the next cycle. We present the results of our comparisons showing the scatter in measured Strehl ratios and our best recommendations for computing an accurate Strehl ratio.

Direct detection and characterization of terrestrial extrasolar planets are now a high-priority scientific program where new major results from extremely large telescopes (ELTs) are expected. This application is also the most demanding for the adaptive optics (AO) and the mirror segment cophasing. To optimize the fundamental performances of an ELT in high-contrast imaging, we compare the effects of segment cophasing errors with the effects of each AO residual phase errors (wavefront sensor noise, fitting, aliasing, servo-lag) on the long-exposure point-spread function halo. We emphasize that an adaptive correction of the differential segment piston at a nanometric level is needed to keep the contrast gain provided by a high-order AO. We show the potential advantages of an adaptive primary mirror for this purpose. Lastly, we present the planet detection performances in the photon-noise-limited case for different telescopes, AO parameters, and observational conditions (star magnitudes and sites).

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.

High dynamic range coronagraphy targeted at discovering planets around nearby stars is often associated with monolithic, unobstructed aperture space telescopes. With the advent of extreme adaptive optics (ExAO) systems with thousands of sensing and correcting channels, the benefits of placing a near-infrared coronagraph on a large segmented mirror telescope become scientifically interesting. This is because increased aperture size produces a tremendous gain in achievable contrast at the same angular distance from a point source at Strehl ratios in excess of 90\% (and at lower Strehl ratios on future giant telescopes such as the Thirty Meter Telescope). We outline some of the design issues facing such a coronagraph, and model a band-limited coronagraph on an aperture with a Keck-like pupil. We examine the purely diffractive challenges facing the eXtreme AO Planetary Imager (XAOPI) given the Keck pupil geometry, notably its inter-segment gap spacing of 6~mm. Classical Lyot coronagraphs, with hard-edged occulting stops, are not efficient enough at suppressing diffracted light, given XAOPI's scientific goal of imaging a young Jupiter at a separation as close as 0.15 arcseconds (4λD at H on Keck) from its parent star. With a 4000 channel ExAO system using an anti-aliased spatially-filtered wavefront sensor planned for XAOPI, we wish to keep diffracted light due to coronagraphic design at least as low as the noise floor set by AO system limitations. We study the band-limited Lyot coronagraph (BLC) as a baseline design instead of the classical design because of its efficient light suppression, as well as its analytical simplicity. We also develop ways of investigating tolerancing coronagraphic mask fabrication by utilizing the BLC design's mathematical tractability.

The ultimate limitation of visible light high-dynamic-range imaging systems such as shaped pupil coronagraphs comes from scattering caused by imperfections in the optical surfaces of the collecting system, and from the non-uniform reflectivity of those surfaces. This paper focuses on the correction of these imperfections using two deformable mirrors in a zero path length difference Michelson interferometer. Simulations show the advantages and limitations of introducing such a device into a wavefront control loop. Laboratory work shows progress towards high resolution amplitude control.

The separation principle of optimal adaptive optics control is derived, and definitions of controllability and observability are introduced. An exact finite dimensional state space representation of the control system dynamics is obtained without the need for truncation in modes such as Zernikes. The uncertainty of sensing uncontrollable modes confuses present adaptive optics controllers. This uncertainty can be modeled by a Kalman filter. Reducing this uncertainty permits increased gain, increasing the Strehl, which is done by an optimal control law derived here. A general model of the atmosphere is considered, including boiling.

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.

We report on observations with MACAO-VLTI to feed the VLT Interferometer in November 2003. The purpose of this observing run was to optimize the feed to the VLTI by varying certain parameters of the curvature AO system and of the interferometer instrument VINCI. All along the main concern about this instrument combination was the differential piston introduced by 2 independent AO systems. A special so-called “piston removal algorithm” has been developed especially for this purpose. Each DM Influence Function is carefully characterized and a pure piston mode is defined to compensate piston over the pupil produced by a given voltage set. Piston is reduced by ~20 using this algorithm. It was found that decreasing the system main gain, while reducing strehl ratio, also reduces high frequency vibrations on the DM and therefore OPD variations. A control frequency of 420 Hz instead of the nominal 350 Hz was found to improve substantially the coupling by reducing the excitation of the DM resonance (~700Hz). On bright stars, an improvement of a factor of 30 in the flux injection into the VINCI fibers was measured. Following these tests a successful observation of the active nucleus of NGC 1068 was performed leading to a visibility of 40.4±5.4% on an average baseline of 45.84 m. The K magnitude in the 60 mas central source is 9.2±0.4. The results already put some interesting constraints on the inner torus and central engine of the nucleus of NGC 1068 but mostly show that the combination MACAO-VLTI and VINCI opens the realm of extragalactic astronomy to interferometry.

NACO is a VLT/Yepun instrument which provides adaptive optics corrected images in the near and thermal infrared. It is composed of the NAOS adaptive optics system and of an infrared imager CONICA. NACO has been operating since October 2001 and has already delivered a large amount of scientific results in various fields, eg the Solar System (Titan), the Interstellar Medium (outflows in Orion-OMC1), the Galactic Center, the central regions of AGN and ULIRG, ... We present the instrument performance in terms of image quality after two years of operation at Paranal. We first remind the system performance obtained from simulations, design, tests and compare them to the original specifications. We point out the telescope vibrations as a source of performance degradation. We then evaluate the impact of these vibrations on the Strehl ratio. We eventually analyze studies of the telescope vibrations to identify the systems that could excite the telescope vibration modes.

An on-line estimation of turbulence parameters (r₀, L₀ and wind speed) and Adaptive Optics (AO) performance using NAOS [Nasmyth Adaptive Optics System] is presented. The method is based on the reconstruction of open-loop data from deformable mirror voltages and residual wavefront sensor slopes obtained in closed loop. This dedicated tool implemented in the real time computer of the NAOS system (first AO of the Very Large Telescope) allows without any loop opening to automatically monitor and display (every 15 seconds) both the atmospheric conditions and the system performance. We have validated the algorithm and tested its robustness on simulated and experimental data (both in laboratory and on sky). Using data obtained during more than two years of operations, statistical study on NAOS performance and turbulence characteristics are proposed. An on-line estimation of turbulence parameters (r₀, L₀ and wind speed) and Adaptive Optics (AO) performance is presented.

SINFONI is an Adaptive Optics assisted near infrared Integral Field Spectrometer, currently in the process of installation and commissioning at the Cassegrain focus of VLT Unit Telescope 4 (YEPUN) in Paranal (Chile). The focal plane instrument (SPIFFI) provides simultaneous spectra of 2048 contiguous spatial pixels covering a two dimensional field of view with almost 100% spatial fill factor and with a spectral resolution of ~3500 in the J, H and K bands. It is fed by the Adaptive Optics Module, a 60 elements bimorph deformable mirror technology / curvature sensing system, derived from MACAO and upgraded to Laser Guide Star operations. This papers reports on the Adaptive Optics Module first light (May 31st 2004). Performances in Natural Guide Star mode were validated during the first commissioning and tests were carried out in preparation to the Laser Guide Star mode. Combined operations of the AO-Module with SPIFFI will start during the second commissioning in July. SINFONI is scheduled to be offered to the community in Natural Guide Star mode in April 2005. The commissioning of the instrument in Laser Guide Star mode will take place in the course of 2005 after successful completion of the Laser Guide Star Facility commissioning.

The accurate calibration of an AO system is fundamental in order to reach the top performance expected from design. To improve this aspect, we propose procedures for calibrating a curvature AO system in view of optimizing performances and robustness, based on the experience accumulated by the ESO AO team through the development of MACAO systems for VLTI and SINFONI. The approach maximizes the quality of the Interaction Matrix (IM) while maintaining the system in its linear regime and minimizing noise and bias on the measurement.

When doing high angular resolution imaging with adaptive optics (AO), it is of crucial importance to have an accurate knowledge of the point spread function associated with each observation. Applications are numerous: image contrast enhancement by deconvolution, improved photometry and astrometry, as well as real time AO performance evaluation. In this paper, we present our work on automatic PSF reconstruction based on control loop data, acquired simultaneously with the observation. This problem has already been solved for curvature AO systems. To adapt this method to another type of WFS, a specific analytical noise propagation model must be established. For the Shack-Hartmann WFS, we are able to derive a very accurate estimate of the noise on each slope measurement, based on the covariances of the WFS CCD pixel values in the corresponding sub-aperture. These covariances can be either derived off-line from telemetry data, or calculated by the AO computer during the acquisition. We present improved methods to determine 1) r₀ from the DM drive commands, which includes an estimation of the outer scale L₀ 2) the contribution of the high spatial frequency component of the turbulent phase, which is not corrected by the AO system and is scaled by r0. This new method has been implemented in an IDL-based software called OPERA (Performance of Adaptive Optics). We have tested OPERA on Altair, the recently commissioned Gemini-North AO system, and present our preliminary results. We also summarize the AO data required to run OPERA on any other AO system.

The adaptive optics system of the 6.5m MMT, based on a deformable secondary mirror has been of the sky now for 6 runs of roughly 2 weeks each. Altogether its performance has been quite satisfactory with a crop of science results. However, even if the mirror has shown it promises, it has proven difficult to improve the system in terms of wavefront quality much beyond what it achieved during 1st light. In particular, it has not been possible to improve image quality by using a larger number of modes than the 52 modes used originally. One reason for this behavior could be that the interaction matrix used to build the AO controller has been measured in lab conditions using a different optical set-up than the one on the telescope. In a Cassegrain adaptive secondary AO system measuring the interaction matrix in the way all other AO systems do is impossible when the secondary is mounted on the telescope. In this paper, we present a way of measuring the interaction matrix on the telescope using real natural guide stars as sources. We present simulations results that show that this method can be used to measure the interaction matrix to a high signal-to-noise ratio.

This paper is a continuation of the characterization of adaptive optics (AO) at Keck Observatory (SPIE 5169-01). The bandwidth and measurement noise error terms are often the important sources of wave-front error. Here, we show how the magnitude of these two terms is estimated. First, the Bayesian wave-front reconstructor employed at Keck Observatory is presented and shown to perform better than a conventional SVD reconstructor. A novel technique used to estimate the size of the spot on a Shack-Hartmann wave-front sensor quad cell detector is introduced, along with experimental results using this technique. The spot size is an essential component of the dynamic model of the AO system, which is presented and used to find the bandwidth and noise error terms.

Adaptive Optics (AO) systems provide real time correction for atmospherical aberrations. They have become an indispensable tool for ground based astronomical observations. However, correction provided by AO is only partial. Further correction can be achieved using post-processing techniques. Post-processing techniques such as deconvolution rely on a good estimation of the long exposure Point Spread Function (PSF). In the case of Solar Physics obtaining a long exposure PSF can be particularly difficult due to the lack of point sources in the field of view and the highly variable seeing conditions. We present a method to estimate the long exposure PSF of an AO corrected image using AO loop data. AO closed loop data provides enough information about the residual aberrations that were not corrected by the system and about the seeing conditions present at a certain time. With this information an estimated long exposure PSF can be constructed for each captured image. The PSF can be used to deconvolve the images. We will be presenting first results of applying this method to solar images.

We will report on the 4-year activities performed by the European Research and Training Network dedicated to Adaptive Optics for Extremely Large Telescopes. This Research Network, funded by the European Commission, has contributed to the development of MCAO techniques which are being evaluated with the so-called MCAO demonstrator (MAD) as well as to several original on-sky wavefront sensing methods for the cophasing of large aperture telescope. We will present an overview of the results obtained in the frame of this project.

The Nasmyth Adaptive Optics Multipurpose Instrument (NAOMI) is the adaptive optics (AO) platform on the 4.2m William Herschel Telescope (WHT) at the Isaac Newton Group of Telescopes (ING). Until recently NAOMI has been concentrating on near infrared observations using the Isaac Newton Group Red Imaging Device (INGRID). Recent developments have added an extra optical port to NAOMI. The observer can now rapidly switch between infrared and optical instrumentation during AO observing, making the system more appealing for visiting instruments. To allow for the operation of the common user optical spectrograph OASIS, a new optical path was created around the existing NAOMI optics. Various mechanisms were also added to the whole optical system. The OASIS beam was reshaped to f/20. The original optical/IR beam remains unchanged at f/16, and forms a new universal science port (USP). The existing Nasmyth Calibration Unit (NCU) has been replaced with a new design. This new NCU has multiple fibre-fed light sources that include continuum and arc lamps. The intensity of light can be individually adjusted via computer control. A new acquisition camera is mounted such that it can be used simultaneously with the spectral lamps. Software upgrades now allow faster deformable mirror calibration. A moveable mirror is used to select which science port will receive the light. Enhancements to the NAOMI AO system are discussed in this paper and suggestions for possible future upgrades.

This paper describes the preliminary optomechanical design and analysis of the Gemini Adaptive Optics Bench being built by EOS Technologies, Inc. The overall optical arrangement is described, the optical tolerances are discussed, and an overview of the optomechanical packaging is provided. Emphasis is placed on integrated modeling of the optomechanical system to predict the effect of mechanical deformation on optical performance

The ESO Multi-conjugate Adaptive optics Demonstrator (MAD) is a prototype intended to be tested at the VLT Nasmyth focus. With its development raises the problem of calibration of an AO system composed of several correcting devices and wave front sensors. One part of this process is the calibration of the static aberrations of the system, always present in spite of the best efforts made during the design, the manufacturing of the optics and their alignment. In this paper we present a study to find an optimized way to correct for the static aberrations in the scientific FoV of an MCAO system. Thanks to images from the camera, the WF error in the FoV is computed, the contribution of several altitudes reconstructed, and finally projected on the deformable mirrors in order to compensate for the measured aberrations. This technique, inspired from the calibration of the static aberration of the system NAOS-CONICA, allows bringing the best quality to the scientific instrument fed by an MCAO system, by taking the most of the presence of correcting devices in the optical path.

Work is underway at the University of Chicago and Caltech Optical Observatories to implement a sodium laser guide star adaptive optics system for the 200 inch Hale telescope at Palomar Observatory. The Chicago sum frequency laser (CSFL) consists of two pulsed, diode-pumped, mode-locked Nd:YAG lasers working at 1.064 micron and 1.32 micron wavelengths. Light from the two laser beams is mixed in a non-linear crystal to produce radiation centered at 589 nm with a spectral width of 1.0 GHz (FWHM) to match that of the Sodium-D2 line. Currently the 1.064 micron and 1.32 micron lasers produce 14 watts and 8 watts of TEM-00 power respectively. The laser runs at 500 Hz rep. rate with 10% duty cycle. This pulse format is similar to that of the MIT-Lincoln labs and allows range gating of unwanted Rayleigh scatter down an angle of 60 degrees to zenith angle. The laser system will be kept in the Coude lab and will be projected up to a laser launch telescope (LLT) bore-sited to the Hale telescope. The beam-transfer optics, which conveys the laser beam from the Coude lab to the LLT, consists of motorized mirrors that are controlled in real time using quad-cell positioning systems. This needs to be done to prevent laser beam wander due to deflections of the telescope while tracking. There is a central computer that monitors the laser beam propagation up to the LLT, the interlocks and safety system status, laser status and actively controls the motorized mirrors. We plan to install a wide-field visible camera (for high flying aircraft) and a narrow field of view (FoV) IR camera (for low-flying aircraft) as part of our aircraft avoidance system.

In preparation for upcoming sodium laser guide star for adaptive optics, a spectroscopic study of the amount of sodium, present in the Earth atmosphere, has been undertaken. Preliminary results of almost 3 years of monitoring are presented here.

Recently, the progress in adaptive optics makes the cone effect of Rayleigh laser guide stars be solved fairly. So that the applications of this kind of beacon in adaptive optics, especially in multiconjugate adaptive optics (MCAO) presents a bright future once again. The photon flux density required by the wavefront sensor of MCAO with certain performance is proportional to the number of layers. This results in that the laser energy required by guide stars for "classical" MCAO is very high. In the "new concept" MCAO, however, the Rayleigh beacons are formed by light scattered from whole higher atmosphere but not only a selected thin layer. Then the required laser energy degrades greatly.

It is necessary for an adaptive optics system to be excepted to achieve established signal-noise ratio that enough signal photon fluxes are there in every subaperture. This requests that either the object imaged is bright enough or there is a bright guide star within the field of view. However, it is unfortunately as often as not in the case in nature and the artificial guide stars have need for. There are two kinds of artificial beacons up to now. They are sodium laser guide star and Rayleigh guide star. The latter among which is generated by the Rayleigh scatter of laser beam from stratosphere. More specially, the laser beam transmitted by ground transmitter propagates upward and undergoes the absorption and the scatter of the atmosphere along the way. It is obvious that only the scattering of the atmosphere within specified altitude range is beneficial. So we always hope that the Rayleigh scattering in this range would be strong and the absorption would be weak to the greatest extent. Under stated altitude, both the scattering and the absorption are the weaker the better. Either the absorbance or the scatterance is dependents on the wavelength of the laser beam and relates to the atmospheric constitution. In this paper, the optimum wavelength for Rayleigh laser beacons is presented by striving for relative extreme values of the transmissivity and the scattering.

In laser beam propagation through the atmosphere under condition where strong scintillation is present, real zeros can appear in the beacon field. On these zero points the phases are undetermined, which are called branch points. The occurrence of branch points causes the conventional least squares phase estimation to fail. The scintillation index is defined of wave front sensor. The relations between branch point number and index versus Rytov variance are simulated numerically. The number of branch point increases with Rytov variance and the index increases and saturates with Rytov variance. The branch point is not only related to Rytov variance but also Fresnel number. Under the given Rytov variance, the larger Fresnel has the more branch point number. The corrected Strehl ratios are compared with least square method and extended least square method for various turbulent conditions.

After more than two years of very successful operation in NGS mode, the VLT Shack-Hartmann AO system NAOS will be upgraded to be operational with the VLT LGS in late 2004. The implementation concerns a new STRAP tip-tilt sensor, an optical path including the trombone to accommodate for LGS height variations, a LIDAR device to measure the initial LGS height, and many high and low level software changes (real-time computer, instrument control, templates, preparation software, etc.). The paper presents this upgrade concept as well as some analysis of the predicted performance of NAOS-LGS.

We propose a practical system that can provide a large number of high performance artificial stars, of the order of a few hundred, using an array of small mirrors on an airship supported platform illuminated from the ground by a laser. Our concept offers several advantages over other guide star schemes: Airborne mirror arrays can furnish tip-tilt information; they also permit a considerable reduction in the total ground-laser power required; high intensity guide stars with very small angular image size are possible; and finally they offer very low scattered parasite laser light. More basic & simpler launch-laser & AO technologies can therefore be employed, with potentially huge cost savings, with potentially significant improvement in the quality of the AO correction. The general platform scheme and suitable lift technologies are also discussed. A novel concept for achieving precise positioning is presented whereby the platform & the lifting vehicle are linked by a tether, the platform having a degree of independent control. Our proposal would employ as the lift vehicle an autonomous high altitude airship of the type currently under widespread development in the commercial sector, for use as hubs for telecommunication networks, mobile telephone relay stations, etc.

We present the development status of the laser system for Subaru Laser Guide Star Adaptive Optics System. We are manufacturing the quasi-continuous-wave sum frequency laser as a prototype. The optical efficiency of sum frequency generation normalized by the mode-locked fundamental YAG (1064 nm) laser output power is achieved to be 14 % using the non-linear crystal, periodically poled potassium titanyl phosphate (PPKTP). Output power at sodium D2 line was about 260 mW. The optical relay fiber and the laser launching telescope are also described in this paper. For the optical relay fiber, we are testing an index guided photonic crystal fiber (PCF), whose core material is filled by fused silica, and whose clad has close-packed air holes in two dimension. The coupling efficiency was evaluated as about 80 % using 1mW He-Ne laser. We introduce the design of laser launching telescope (LLT), which is a copy of VLT laser launching telescope, and the interface to the Subaru Telescope.

The laser guide star adaptive optics (AO) module for the Subaru Telescope will be installed at the f/13.9 IR Nasmyth focus, and provides the compensated image for the science instrument without change of the focal ratio. The optical components are mounted on an optical bench, and the flexure depending on the telescope pointing is eliminated. The transferred field of view for the science instrument is 2 arcmin diameter, but a 2.7 arcmin diameter field is available for tip-tilt sensing. The science path of the AO module contains five mirrors, including a pair of off-axis parabolic mirrors and a deformable mirror. It has also three additional mirrors for an image rotator. The AO module has a visible 188-element curvature based wavefront sensor (WFS) with photon-counting avalanche photodiode (APD) modules. It measures high-order terms of wavefront using either of a single laser (LGS) or natural guide star (NGS) within a 2 arcmin diameter field. The AO module has also a visible 2 x 2 sub-aperture Shack-Hartmann WFS with 16 APD modules. It measures tip-tilt and slow defocus terms of wavefront by using a single NGS within a 2.7 arcmin diameter field when a LGS is used for high-order wavefront sensing. The module has also an infrared 2 x 2 sub-aperture Shack-Hartmann WFS with a HgCdTe array as an option. Both high- and low-order visible WFSs have their own guide star acquisition units with two steering fold mirrors. The AO module has also a source simulator. It simulates LGS and NGS beams, simultaneously, with and without atmospheric turbulence by two turbulent layer at about 0 and 6 km altitudes, and reproduces the isoplanatism and the cone effect for the LGS beam.

This paper describes a random vibration, finite element analysis (FEA), performed on the Gemini Laser Launch Telescope (LLT) using ANSYS. A highly detailed model, originally created for static analysis, served as a baseline model but required extensive simplification to be used for random vibration analysis. A reduced spectrum PSD was also required. This paper describes the simplification process and summarizes the results of the analysis.

The W. M. Keck Observatory Adaptive Optics (AO) team recently celebrated a milestone first AO-corrected image with the new Laser Guide Star (LGS) system. This paper details focus and pointing changes implemented for the LGS AO system. The combination of variable sodium altitude, elevation-dependent distance to the LGS, off-axis projection, and equipment flexure require both focus and pointing adjustments to keep the laser spot located and its size minimized on the wavefront sensor. We will describe the current approach to LGS focus and pointing-compensation adjustments, and provide some insight into issues seen thus far during engineering activities at the W. M. Keck Observatory.

Simultaneous wavefront measurements are planned at the 6.5 m MMT telescope of five dynamically refocused Rayleigh laser beacons (RLGS) and a bright natural star to demonstrate tomographic wavefront reconstruction. In this paper, we summarize preliminary data recorded from the five laser beacons during the first telescope run at the MMT in June 2004. Beam projection is from behind the secondary of the MMT to form a regular pentagon of beacons on the sky with a radius of 60 arcseconds around the natural star. Beacon images are recorded over a range gate from 20 to 30 km, with dynamic refocus optics in the focal plane to remove perspective elongation (Stalcup, et. al., these proceedings). Separate externally synchronized Shack-Hartmann sensors record wavefront measurements of the beacons and the star, which will yield the first 33 Zernike modes from each wavefront measurement. A linear tomographic reconstructor, implemented as a matrix multiplication of the combined Zernike modal amplitudes from all five RLGS, has been computed to estimate contributions to the atmospheric aberration in two layers at 0 and 6 km. To validate the tomographic approach, the wavefront of the natural star will be predicted by computing the sum of the aberration in the direction of the star, and the prediction compared to simultaneous measurements recorded from the star directly.

The wavefront-sensor is one of the most important components of any adaptive optics (AO) system. The simplicity of the Shack-Hartmann sensor has made it a popular choice for such systems. Its accuracy, which largely determines its performance depends on having a good and robust centroid algorithm. Despite a large number of studies, the general recipe for selecting the best centroiding algorithm and best pixel size in a Shack-Hartmann wavefront sensor is still lacking. We combine analytical theory with numerical simulations to compare various flavors of centroiding algorithms (thresholding, windowing, correlation, quad-cell) under different conditions of photon flux, read-out noise, and sampling. It is shown that the choice of the best method depends on those parameters. At very low signal to noise ratio, the performance of the quad-cell is close to optimum.

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.

A new hybrid optical detector is described that has many of the attributes desired for the next generation AO wavefront sensors. The detector consists of a proximity focused MCP read out by four multi-pixel application specific integrated circuit (ASIC) chips developed at CERN ("Medipix2") with individual pixels that amplify, discriminate and count input events. The detector has 512 x 512 pixels, zero readout noise (photon counting) and can be read out at 1kHz frame rates. The Medipix2 readout chips can be electronically shuttered down to a temporal window of a few microseconds with an accuracy of 10 nanoseconds. When used in a Shack-Hartman style wavefront sensor, it should be able to centroid approximately 5000 spots using 7 x 7 pixel sub-apertures resulting in very linear, off-null error correction terms. The quantum efficiency depends on the optical photocathode chosen for the bandpass of interest. A three year development effort for this detector technology has just been funded as part of the first Adaptive Optics Development Program managed by the National Optical Astronomy Observatory.