Over the past two years ESO has reinforced its efforts in the field of Adaptive Optics. The AO team has currently the challenging objectives to provide 8 Adaptive Optics systems for the VLT in the coming years and has now a world-leading role in that field. This paper will review all AO projects and plans. We will present an overview of the Nasmyth Adaptive Optics System (NAOS) with its infrared imager CONICA installed successfully at the VLT last year. Sodium Laser Guide Star plans will be introduced. The status of the 4 curvature AO systems (MACAO) developed for the VLT interferometer will be discussed. The status of the SINFONI AO module developed to feed the infrared integral field spectrograph (SPIFFI) will be presented. A short description of the Multi-conjugate Adaptive optics Demonstrator MAD and its instrumentation will be introduced. Finally, we will present the plans for the VLT second-generation AO systems and the researches performed in the frame of OWL.

The purpose of this paper is to report on new adaptive optics (AO) developments at the W. M. Keck Observatory since the 2000 SPIE meeting. These developments include completion of the Keck I AO system, interferometric combination of the full apertures of the two Keck telescopes using AO on both telescopes, commissioning of two science instruments with the Keck II AO system, first projection of the Keck II sodium laser beacon, progress on laser guide star AO, improved automation of the AO systems and a diversity of AO science programs.

We present an overview of Subaru Cassegrain adaptive optics system and its performance verified at the engineering run. The system is based on a curvature wavefront sensor with 36-element sub-apertures and a bimorph deformable mirror with identical number of elements. We had the first light in Dec. 2000. The AO system has been in service for two instruments, IRCS; infrared camera and spectrograph, and CIAO; coronagraph imager with adaptive optics. The Strehl ratio at the K band is around 0.30 under 0.4- 0.5 arcsec K-band seeing condition for bright guide stars. The sensitivity of the wavefront sensor is so high that we have significant improvement of image quality even for a faint guide star down to R=18^th magnitude. The measurement of stars in a globular cluster suggests an isoplanatic angle, about 40 arcsec, wider than that expected from the equivalent turbulence layer assumed at the height of 6.5 km. The system has been offered for common use since Apr. 2002. Some scientific results using this AO system are shown in this paper.

A 36-elements curvature adaptive optics (AO) system has been operating on the Subaru telescope for about one and a half year. We achieved a Strehl ratio of 0.3 in the K-band, which is a rather smaller value than we expected. While we are investigating the discrepancy between the obtained performance and the simulated performance of the current AO system and we are also improving the current AO system in terms of the Strehl performance and the observing efficiency. Meanwhile we have started to plan a next generation of Subaru AO system. Two major upgrades are proposed in this paper. One is to increase the number of subapertures as much as possible. Practically, the number of subapertures lies between 100 and 200. The size of subaperture becomes half to one-third of that of the current system and we expected that the K-band Strehl ratio will improve to more than 0.6. The first light of the higher order curvature AO system is scheduled for 2004. Another upgrade plan is to use a laser guide star (LGS). A single LGS is projected at the sodium layer with an output power of 4 W. Conceptual designs for the laser system, beam relay system, laser launching telescope and control system have begun. The first test of launching laser from Subaru telescope will be in 2005.

A laser guided adaptive optics system called UnISIS -- University of Illinois Seeing Improvement System -- has been commissioned at the Mt. Wilson 2.5-m Telescope. The UnISIS laser guide star is created via Rayleigh scattering of 351 nm photons from a 30 W excimer laser. The laser guide star is focused at an altitude of 20 km above msl. The UnISIS adaptive optics system sits at the fixed f/30 Coude focus of the 2.5-m telescope while the 30 W excimer laser sits on the observatory ground floor. The collimated laser beam is projected first into the Coude room where it is converted to f/30 and projected into the sky off the 2.5-m primary mirror. We describe the practical experience gained in installing and commissioning UnISIS, and we present simulations of the expected system performance based on the characteristic C_n² distribution above Mt. Wilson.

The multi-conjugate adaptive optics (MCAO) system design for the Gemini-South 8-meter telescope will provide near-diffraction-limited, highly uniform atmospheric turbulence compensation at near-infrared wavelengths over a 2 arc minute diameter field-of-view. The design includes three deformable mirrors optically conjugate to ranges of 0, 4.5, and 9.0 kilometers with 349, 468, and 208 actuators, five 10-Watt-class sodium laser guide stars (LGSs) projected from a laser launch telescope located behind the Gemini secondary mirror, five Shack-Hartmann LGS wavefront sensors of order 16 by 16, and three tip/tilt natural guide star (NGS) wavefront sensors to measure tip/tilt and tilt anisoplanatism wavefront errors. The WFS sampling rate is 800 Hz. This paper provides a brief overview of sample science applications and performance estimates for the Gemini South MCAO system, together with a summary of the performance requirements and/or design status of the principal subsystems. These include the adaptive optics module (AOM), the laser system (LS), the beam transfer optics (BTO) and laser launch telescope (LLT), the real time control (RTC) system, and the aircraft safety system (SALSA).

The adaptive optics system for the Gemini South telescope, currently in the design phase, consists of several major subsystem. The largest subsystem, called the AO module, contains most of the optics and electronics and is mounted on one of the Cassegrain instrument ports. The initial system will be a conventional laser guide star AO system, but the plan is to eventually expand it to a multi-conjugate system. The system is being designed to readily add the components necessary to upgrade to a multi-conjugate system. This paper describes the design challenges encountered and solutions that were derived for the AO module design. The complexity of the multi-conjugate version is illustrated, including optical, mechanical, electronic and controls issues.

Since a few years we are developing a low cost adaptive optics system for the GI2T optical interferometer. Our AO is based on a curvature sensor and a 31 actuator bimorphe mirror. We designed a wavefront sensor using an array of prisms to split the pupil image and photon counting avalanche photodiodes modules as detectors. We present here the design and the first results obtained on a test bench. This AO system will be used for the tests of a laser guide star and for observations of stars and asteroids. Latter, another system will be built to equip GI2T-Regain with two AO.

The goal of this paper is to discuss the turbulent effects on the laser beam of the lunar laser ranging (LLR), and to use the real-time tilt compensation for the LLR. In this new technique, a small area near the retroreflector array on the moon surface will be used as an extended source to detect the wavefront tilt. Then the absolute difference algorithm will be used to calculate the wavefront tilt and to reconstruct it, and it will be used to drive a tip-tilt mirror in the laser transmit path to carry on the real-time tilt compensation for the laser beam on the LLR. After the compensation, the returned laser photons from the moon retroreflector to the ground telescope will be increased a factor of 6 to 40, depend on the turbulence.

We discuss the image improvement from an adaptive optics system that selectively corrects for phase perturbations with large angular coherence lengths. Selecting phase perturbations with large angular coherence lengths effectively sets the correction to turbulence of all spatial frequencies at the ground and to turbulence of progressively lower spatial frequencies at higher altitudes. The performance of a high-order curvature system (85 elements) on a small telescope (4 meters) across a field of view of roughly six arcminutes diameter is simulated using Monte Carlo simulations. The implementation studied assumes a single correcting element conjugate to the ground with multiple wave front sensors each pointed at a different star within the field of view. The image full-width at half maximum (FWHM) is reduced by up to a factor of two over the uncorrected case. Even though the number of guide stars is large (n~3), the sky coverage is similar to that for a classical adaptive optics system since the acquisition field is much larger (~35 square arcminutes). In principle the approach could be extended to multiple laser guide stars and larger apertures. The requirements for the laser are relaxed since the sampling of turbulence is preferentially at low-altitudes (e.g. Rayleigh beacons).

Affordable adaptive optics on small telescopes allow to introduce the technology to a large community and provide opportunities to train new specialists in the field. We have developed a low order, low cost adaptive optics system for the 1.6m telescope of the Mont Megantic Observatory. The system corrects tip-tilt, focus, astigmatisms and one trefoil term. It explores a number of new approaches. The sensor receives a single out-of-focus image of the reference star. The central obstruction of the telescope can free the focus detection from the effect of seeing and allows a very small defocus. The deformable mirror is profiled so as to preserve a parabolic shape under pressure from actuators located at its edge. A separate piezoelectric platform drives the tilt mirror.

We have designed, realized and tested a dedicated software tool defined so as to enable a wide non-specialist community to perform optimal adaptive optics observations with VLT instrument NAOS-CONICA. We first precise the requirements derived from NAOS complexity due to a large number of configurations, ESO/VLT operational policy including service mode observations and limited human interaction during observations, and astronomical observation requirements. We then present the developed software tool, so-called "Preparation Software", that couples a user-friendly interface that accepts observation conditions (including seeing, star magnitude etc...) and an elaborate simulator of adaptive optics based on the NAOS characteristics.

Use of a highly sensitive curvature wavefront sensor (WFS) with avalanche photodiode (APD) detectors at the Gemini North telescope has allowed direct AO guiding on very low mass stars (V=18-20, I=14-16) producing 0.1” images in K’. This resolution (which is near to the 0.07” diffraction limit) has enabled us to conduct ground-based searches for substellar companions (<0.075 M) to within ~3 AU of their primary stars. We have been able to use the faint science targets themselves to close the AO loop. The key to this capability is the zero readout noise, photon-counting APDs used in the curvature WFS. The amplification of incident photons from low luminosity sources allows sufficient signal at the subapertures to reconstruct the aberrated wavefronts with relatively little reconstruction error. This is advantageous compared to typical Shack-Hartmann WFSs which require greater signal from their guide stars to compensate for their CCDs’ readout noise. The technique presented here is currently the only working one from the ground studying such cool and faint targets. Additionally, we report the discovery of 3 new binary stellar systems from a survey of 30 low mass stars (~0.095 M, spectral type M6.0-M7.5, V=18-20) at separations between 0.12-0.29” (3.5-8.3 AU) using this technique.

At TNO TPD we have realized an Adaptive Optics test bench. The bench has an in-house built turbulent atmosphere simulator. For the wavefront sensors there is the possibility to choose between a Shack-Hartmann sensor and a pyramid sensor. Compensation of the wavefront error is performed by a separate tip-tilt mirror and a deformable mirror. Both are off the shelf products. The AO system is controlled by a Multi-Input-Multi-Output control system with 40 actuator channels and 50 sensor channels. The proposed control strategy corresponds to a Linear Quadratic approach, in which the sum of the mean squared wavefront error over the sensor points and the weighted control effort is minimized. In the optimization process the dynamic properties (spatial-temporal correlation) of both the turbulence-induced wavefront error and the mirror/sensor combination are taken into account. Furthermore, important issues like closed-loop stability and robustness are included in the control design. An adaptive control algorithm has been derived, which converges to the LQ-solution and also enables tracking of changes in the characteristics of the turbulent wavefront. This paper presents the first results achieved with the Adaptive optics test bench. It shows that a simplified version of the adaptive feedback control strategy already gives promising results, both implemented in a commonly used AO simulation software package and in real-time on the AO test bench.

NAOS is the first adaptive optics system installed at the VLT 8m telescopes. It was designed, manufactured and tested by a french Consortium under an ESO contract, to provide compensated images to the high angular resolution IR spectro-imaging camera (CONICA) in the 1 to 5 μm spectral range. It is equipped with a 185 actuator deformable mirror, a tip/tilt mirror and two wavefront sensors, one in the visible and one in the near IR spectral range. It has been installed in November at the Nasmyth focus B of the VLT UT4. During the first light run in December 2001, NAOS has delivered a Strehl ratio of 50 under average seeing conditions for bright guide stars. The diffraction limit of the telescope has been achieved at 2.2 μm. The closed loop operation has been very robust under bad seeing conditions. It was also possible to obtain a substantial correction with mV=17.6 and mK=13.1 reference stars. The on-sky acceptance tests of NAOS-CONICA were completed in May 2002 and the instrument will be made available to the European astronomical community in October by ESO. This paper describes the system and present the on-sky performance in terms of Strehl ratio, seeing conditions and guide star magnitude.

Observing at high angular resolution from the ground is not made possible with Adaptive Optics alone, and besides the turbulence residuals, atmospheric refraction, thermal background or instrument's mechanical flexures may also severely limit the gain of optical quality that AO techniques are supposed to provide. We describe here how NAOS, the newly installed AO system on the VLT, has been designed to accommodate for these unavoidable effects. In particular, beam chopping, flexures compensation and AO tracking on reference objects with a significant relative motion will be addressed. It will thus be shown how long term astronomical observations at the diffraction limit can be carried out with an AO system under regular ground level conditions, thanks to the implementation of original technical solutions.

In this communication, we present the progress of the 6.5m MMT adaptive optics system. During the last part of 2001 and the 1^st part of 2002, the system has been validated in the laboratory statically and dynamically with sample frequencies of up to 550 Hz. In June 2002, an attempt has been made to make this system work on the telescope but has been hampered by mechanical failures. However, ease of installation of the system and open-loop operation of the mirror was demonstrated at this occasion and offers reasons to be optimistic on the future of the system. The MMT-AO system is the first AO system to compensate the aberrated wavefront at the telescope's secondary mirror. This approach has unique advantages in terms of optical simplicity, high throughput and low emissivity. Its realization presents many technical challenges, which have now been overcome. Today, the deformable mirror is characterized and accepted. It features a 1.8 mm thick 640mm diameter convex aspheric mirror (manufactured at the Steward Observatory Mirror Lab), mounted on a 50 mm thick ULE reference body with 336 actuators, as well as a cluster of 168 DSP’s and associated analog circuitry for position sensing and actuator driving. The system has been characterized in the laboratory at sampling speeds up to 550 Hz and had been integrated on the telescope.

The paper describes the design of the single conjugate Adaptive Optics system to be installed on the LBT telescope. This system will be located in the Acquisition, Guiding and Wavefront sensor unit (AGW) mounted at the front bent Gregorian focus of LBT. Two innovative key features of this system are the Adaptive Secondary Mirror and the Pyramid Wavefront Sensor. The secondary provides 672 actuators wavefront correction available at the various foci of LBT. Due to the adaptive secondary mirror there is no need to optically conjugate the pupil on the deformable mirror. This allows having a very short sensor optical path made up using small dimension refractive optics. The overall AO system has a transmission of 70 % and fits in a rectangle of about 400×320mm. The pyramid sensor allows having different pupil sampling using on-chip binning of the detector. Main pupil samplings for the LBT system are 30×30, 15×15 and 10×10. Reference star acquisition is obtained moving the wavefront sensor unit in a field of view of 3×2 arcmin. Computer simulations of the overall system performance show the good correction achievable in J, H, and K. In particular, in our configuration, the limiting magnitude of pyramid sensor results more than one magnitude fainter with respect to Shack- Hartmann sensor. This feature directly translates in an increased sky coverage that is, in K band, about doubled with respect to the same AO system using a Shack-Hartmann sensor.

MACAO stands for Multi Application Curvature Adaptive Optics. A similar concept is applied to fulfill the need for wavefront correction for several VLT instruments. MACAO-VLTI is one of these built in 4 copies in order to equip the Coude focii of the ESO VLT's. The optical beams will then be corrected before interferometric recombination in the VLTI (Very Large Telescope Interferometer) laboratory. MACAO-VLTI uses a 60 elements bimorph mirror and curvature wavefront sensor. A custom made board processes the signals provided by the wavefront detectors, 60 Avalanche Photo-diodes, and transfer them to a commercial Power PC CPU board for Real Time Calculation. Mirrors Commands are sent to a High Voltage amplifier unit through an optical fiber link. The tip-tilt correction is done by a dedicated Tip-tilt mount holding the deformable mirror. The whole wavefront is located at the Coude focus. Software is developed in house and is ESO compatible. Expected performance is a Strehl ratio sligthly under 60% at 2.2 micron for bright reference sources (star V<10) and a limiting magnitude of 17.5 (Strehl ~0.1). The four systems will be installed in Paranal successively, the first one being planned for June 2003 and the last one for June 2004.

The design of a detector array intended for use as a Shack-Hartman wavefront sensor is presented. The chip will output voltages that represent local tilts and currents that represent inferred piston information by processing the optical signals from a lenslet array. Each pixel in the array contains four phototransistors, arranged in a square, along with transistors needed to perform algorithms necessary to output signals. Each pixel has four built-in amplifiers to output a voltage for each of the four phototransistors. By combining these voltages off-chip, tilt information is obtained, and allows for positive and negative tilts to be output from a single-supply chip. All pixels contain a self-biasing circuit, allowing tilt information to be consistent across all pixels for apertures that are not uniformly illuminated. Algorithms for inferring piston information are generated by using CMOS transistors in current mode. The piston information is output as a current with a magnitude that is proportional to the actual piston value. The pixels are selected by means of bit-parallel row and column select. The outputs consist of four voltages, four currents to monitor the phototransistor behavior, and one current representing piston. There are inputs that allow the user to set a global piston offset, and overall bias for overriding the amplification of the tilt voltages. Simulations of this design suggest refresh rates in excess of 2kHz are easily attainable. The design of this wavefront sensor is optimized for low light levels and high refresh rates. Prototype detectors will be fabricated using a 0.5micron CMOS process. This detector could greatly simplify the process of wavefront reconstruction, and could even allow for direct hardware control of deformable mirrors in adaptive optics systems with an order of magnitude more channels than are currently used.

Only a very few examples of near-infrared wavefront sensors can be found in the litterature. However, none of these sensors provide routine observation yet. Our sensor is the only one to be operated routinely on a large AO system. Entirely cryogenized, this sensor is built around a so-called HAWAII array from Rockwell (HgCdTe, 1024×1024). It is working in the huge spectral band ranging from 0.8 to 2.55 microns, and may use -when required- all the flux from this very whole band. It allows to switch between several optical configurations in order to match all atmospheric and observing conditions, while its original mechanical design allows to keep, even at cryogenic temperatures, a mechanical stability lower than 4 microns in any position. It also has some particular read-out schemes, allowing to obtain frame rates as high as 1200 Hz while keeping a read-out noise performance of 10 electrons rms/pixel. The analysis of the design parameters (pixel size, field of view) is exposed in this article. Some results, obtained during the comissioning runs at ESO, will also be presented.

In an adaptive optical system, it is essential that the wavefront sensor be accurately calibrated and aligned to the wavefront corrector. For the case of the Shack Hartmann sensor, there are at least three quantities which must be measured: a. the response of the subapertures to local wavefront tilt, b. the location of the zero point for each subaperture from a plane wave input, and c. the spatial relationship between the wavefront sensor subapertures and the wavefront corrector actuators. This paper present a method which verifies the calibration of a Shack Hartmann wavefront sensor by simultaneously measuring static wavefront with a phase shifting interferometer. These measurements were made using an apparatus we constructed in the laboratory to build and test the adaptive optical system for the 6.5 m MMT.

The estimation accuracy of wavefront sensors in strong scintillation is examined. Wave optical simulation is used to characterize the performance of several wavefront sensors in the absence of measurement noise. The estimation accuracy of a Schack-Hartmann sensor is shown to be poor in strong scintillation due primarily to the presence of branch points in the phase function. The estimation accuracy of a unit-shear, shearing interferometer is found to be significantly better than that of a Hartmann sensor in strong scintillation. The estimation accuracy of a phase shifting point diffraction interferometer is shown to be invariant with scintillation.

Use of ground-based observatories for astronomy has been greatly improved through the use of active correction systems based on subaperture wavefront sensing techniques such as Hartmann and curvature sensing. While the resulting performance significantly exceeds the performance of the unaided observatory, the use of a large number of independent subapertures to determine the necessary local corrections results in a requirement for relatively bright guidestars. This, in turn, limits the available area of the sky that supports high quality imagery of target using natural guidestar operation. The use of artificial guidestars increases the available region of the sky for viewing, but the resulting imagery is not as good as is achievable in the vicinity of a natural guidestar. The use of image-based sensing such as focus diverse phase retrieval produces higher quality wavefront sensing, but, if used as the sole WFS machine, generally requires longer processing times than can used for real-time correction. In this paper, we discuss the potential of using secondary wavefront sensing and correction systems within individual instruments to supplement the observatory active system. In particular, we present simulation results demonstrating the performance of a potential real-time focus diverse phase retrieval based WFS&C subsystem. We discuss the required observatory active correction performance, the secondary guidestar characteristics, and the processing speed requirements.

A new tracker is under development at the Starfire Optical Range (SOR). The tracker system's tilt sensor is based on an optical pyramid that creates a quad-cell effect into avalanche photo diodes, sampled at 5000 frames per second. A suite of hardware and software that allows unprecedented flexibility in control system design and implementation delivers the mirror control signals. The control problems associated with this tracking system are interesting due to lightly damped mirror resonances; these dynamics are handled via a tight inner cage loop. Thus, the controller makes use of both optical feedback and mirror position feedback. This paper discusses the design and implementation of the entire tracker system, including sensor characteristics, steering mirror characteristics, electronics, and control algorithms implemented. Experimental results are presented.

The NAOS adaptive optics system was installed in December 2001 on the Nasmyth focus of the ESO VLT. It includes two wavefront sensors: one is working at IR wavelength analysis and the other at visible wavelengths. This paper describes the NAOS Visible Wave Front Sensor based on a Shack-Hartman principle and its performances as measured on the sky. This wavefront sensor includes within a continuous flow liquid nitrogen cryostat: 1) a low noise fast readout CCD camera controlled by the ESO new generation CCD system FIERA using a fast frame rate EEV/Marconi CCD-50 focal plane array. This 128×128 pixels focal plane array has a readout noise of 3 e- at 50 kilopixel/sec/port. FIERA provides remotely controlled readout modes with optional binning, windowing and flexible integration time. 2) two remotely exchangeable micro-lens arrays (14×14 and 7×7 micro-lenses) cooled at the CCD temperature ( -100 °C) within the cryostat. The CCD array is directly located in the micro lenses focal plane at a few millimeters apart without relay optics. 3) Additional opto-mechanical functions are also provided (atmospheric dispersion compensator, flux level control, field of view limitation). On sky performances of the wavefront sensor are presented. Adaptive Optics corrections was obtained with a reference star as faint as a visible magnitude 17 with a band-path of 40 Hz in close loop.

In Astronomy the goal of the Adaptive Optics systems is the real time correction of the aberrations introduced from the turbolence of the air in the wavefront of the observed field of view. A wavefront sensor with pyramidic shape has being developed by a group of Italian researchers that offers the advantage of either variable gain against the wavefront deformation and tunable sampling of the telescope pupil. Single pyramid prototypes were made using the classical figuring and polishing techniques. This approach however, is not only very time consuming but also does not guarantee a uniform repeatability of the optical characteristics of the pyramids requested by this application (the implementation of a high number of these devices is needed for multi-conjugated adaptive optics). We therefore are investigating a manufacturing process for the pyramidal optical components based on the Deep X-ray Lithography (DXRL) technology, using X-ray synchrotron radiation, and exploiting a lithography dedicated beamline already operating at the ELETTRA Synchrotron in Trieste. This method foresees the irradiation of a transparent and amorphous plastic polymer like PMMA (Plexiglass) with a collimated high intensity X-ray beam. The radiation modifies the internal structure of the irradiated polymer that, once immersed into an appropriate chemical bath, permits its dissolution. In this way, by means of a mask and a series of exposures, it is possible to form a four-faces pyramid. After some preliminary tests, a mechanical system has been built to manufacture the plastic pyramids with tight tolerances. The pyramids manufactured with DXRL can be seen as the final product to be implemented in an AO system. To manufacture large numbers of this components (mass production) we are investigating their molding starting from a pyramid template made with DXRL. The manufactured mold, made by electrodeposition of a metal on the template pyramid, could then be used for the production of pyramids by Injection molding or hot embossing.

Shack-Hartmann based wavefront sensors, used to compensate atmospheric turbulence, appear to be less sensitive than cur-vature based wavefront sensors by more than a magnitude. Besides their read noise free APD detectors and different meas-urement principle, the sensitivity of curvature sensors may benefit from the keystone shaped lenslet geometry which opti-mally balances aperture coverage and illumination of individual subapertures. This paper describes the implementation of a keystone shaped lenslet array for the ALFA Shack-Hartmann based AO system. We compare the novel design with hexago-nal shaped lenslets under different operating conditions such as selected modal basis set and number of compensated modes theoretically and in practice.

Until now, only avalanche photodiodes (APD) have been used as the detectors in curvature wavefront sensors in astronomy. This is due to the strict requirements of very short integration time and very low readout noise. In 1999, Beletic et al. invented a new CCD design which should achieve the same performance as APDs but with higher reliability and lower cost. In addition, this CCD has higher quantum efficiency than APD modules and larger dynamic range, eliminating the need for neutral density filters on bright objects. The CCD was designed and fabricated by MIT Lincoln Laboratory in collaboration with ESO and IfA. R. Dorn extensively tested the CCD in laboratory at ESO and proved that it achieves the predicted performance. CFHT is currently implementing this CCD on PUEO, CFHT’s Adaptive Optics system, to assess its performance for the first time in real conditions on the sky for a direct comparison with the current 19 APD detector system. In this article we present the current implementation scheme and discuss the upgrade we foresee for PUEO NUI, a 104-element high-order curvature AO system envisaged to replace the current AO system at Canada-France-Hawaii Telescope.

The objective of the PYRAMIR project is to complement the Calar Alto Adaptive Optics System - ALFA - with a new pyramid wavefront sensor working in the near IR, replacing the previous tip-tilt tracker arm. Here we describe the Science as well as the Technical motivation for such a system. The optical design will be presented, discussing the particular requirements posed by sensing the wavefronts in the infrared like a cooling system for the opto-mechanical components, etc. We will also talk about the components, like the IR detector we plan to use - PICNIC, as one option, the sucessor of NICMOS3 from Rockwell, together with the AO-Multiplexer. It is described how we expect to integrate the system into the optical, machanical, electronical and control architecture of ALFA.

In the pyramid wavefront sensor some dynamic range is accomplished by modulating the optical signal across the four faces of the pyramid before the dissection and detection of the light. Although this can be realized in different ways, including systems which do not require any moving part, we question and discuss the real needs for such a modulation. In fact, when the closed-loop performance is not perfect, some residual errors on the wavefront sensor are expected and one should take care to allow for enough dynamic range to get a linear response within such a residual range. However, the non-corrected aberrations themselves can be considered as a form of modulation. Higher order uncompensated residuals are equivalent to a modulation for the lower compensated modes. We present a preliminary study showing that this sort of 'natural' modulation could be, at least under certain conditions, enough to reach comparable results with respect to dynamical modulation during correction, hence rising the question of the need of a modulation in the realization of the pyramid wavefront sensor.

A demonstrator of the multi-conjugate adaptive optics concept is under construction at ESO and will be installed on the Nasmyth focus of the VLT. This demonstrator called MAD will have two different wavefront sensor channels: Shack-Hartmann and Layer-Oriented; in this article we only describe the Layer-Oriented one. The Layer-Oriented wavefront sensor can select eight reference stars in the two arc-minutes corrected field of view in order to have a maximum of two references in each quarter of the field. XY stages will remotely adjust the position of each reference star selector. The starlight will be fed onto two detectors and two completely independent loops will drive the deformable mirrors, one conjugated to the ground and the other to an altitude of approximately 8 km. The Layer-Oriented wavefront sensor will use the same CCDs than the Shack-Hartmann channel and the pupil will be divided into 9×9 subapertures both for the high and for the ground layer. The spatial sampling of the subapertures will be different for the two CCDs and their integration time will be tuned to typical values of the conjugated altitudes characteristic wind speed. The overall status of the instrument with respect to optics, mechanics, electronics and software is given hereafter. We also summarize the progress on the procurement phase and give the time schedule for the assembling, integration and testing phases.

We describe some novel technical approaches to implement multi-pyramid wavefront sensing, partially extendable to single pyramid and to any MCAO system. First we introduce an achromatic version of the pyramid, which allows for a much better spatial resolution on the pupil and also relaxes the specifications in term of turned edges. Another item that we discuss is the distribution of tolerances in a layer-oriented AO system which makes attractive, at least in some cases, the usage of pairs of lenslet arrays, leaving only the pyramids free to move over the Field of View, hence relaxing the requirements in terms of roll and yaw in their positioning. Then we discuss the effect of pupil distortion occurring in the layers above the ground during the open loop phases of a MCAO system. Finally we discuss a possible usage of the Modulation Transfer Function as a valuable tool to estimate the correction of a certain Zernike polynomial, achievable with a pyramid wavefront sensor. These items are sketched along with a status of their practical implementation and possible future extensions.

Multi-Conjugate Adaptive Optics (MCAO) is working on the principle to perform wide field of view atmospheric turbulence correction using many Guide Stars located in and/or surrounding the observed target. The vertical distribution of the atmospheric turbulence is reconstructed by observing several guide stars and the correction is applied by some deformable mirrors optically conjugated at different altitudes above the telescope. The European Southern Observatory together with external research institutions is going to build 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 telescope OWL. In this paper we present the conceptual design of the MAD module that 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.

The European Southern Observatory (ESO) and the Max Planck Institut fur extraterrestrische Physik (MPE) are jointly developing SINFONI, an Adaptive Optics (AO) assisted Near Infrared Integral Field Spectrometer, which will be installed in the first quarter of 2004 at the Cassegrain focus of YEPUN (VLT UT4). The Adaptive Optics Module, a clone of MACAO, designed and built by ESO, is based on a 60 elements curvature system. It feeds the 3D spectrograph, SPIFFI, designed and built by MPE, with higher than 50% K band Strehl for bright (V<12) on-axis Natural Guide Stars (NGS) and less than 35 mas/hour image motion. The AO-Module will be the first curvature AO system operated in Laser Guide Star (LGS) mode, using a STRAP system for the tip/tilt sensing. The Strehl performance in the LGS mode is expected to be better than 30% in K band.

The Lick Observatory laser guide star adaptive optics system has undergone continual improvement and testing as it is being integrated as a facility science instrument on the Shane 3 meter telescope. Both Natural Guide Star (NGS) and Laser Guide Star (LGS) modes are now used in science observing programs. We report on system performance results as derived from data taken on both science and engineering nights and also describe the newly developed on-line techniques for seeing and system performance characterization. We also describe the future enhancements to the Lick system that will enable additional science goals such as long-exposure spectroscopy.

A rationale is presented for the use of a relatively low-altitude (15km) Rayleigh Laser Guide Star to provide partial adaptive optics correction across a large fraction of the sky on the 4.2m William Herschel Telescope. The scientific motivation in relation to the available instrumentation suite is discussed and supported by model performance calculations, based on observed atmospheric turbulence distributions at the site. The proposed implementation takes the form of a laser system, beam diagnostics, tip-tilt mirror and beacon launch telescope, together with a range-gated wavefront sensor and processing system. It is designed to operate in conjunction with the telescope’s existing facility-class natural guide star AO system, NAOMI. Aspects of the proposed implementation are described as well as the technical features related to the system model and the error budget. In a separate paper the NAOMI AO system itself is presented. Other papers describe a demonstrator system and preliminary Rayleigh beacon wavefront sensing measurements at the site.

This paper describes the upgrades to the Keck II Adaptive Optics (K2 AO) system needed for laser guide star observing. The upgrade, including integration with the laser, is scheduled for completion in the winter of 2003. This upgrade includes the addition of a Low Bandwidth Wavefront Sensor (LBWFS) measuring focus and higher order terms, and a Lawrence Livermore National Lab quad-lens avalanche photodiode detector which monitors tip/tilt. Both observe a dim natural guide star. LBWFS corrections are applied as corrections to the high bandwidth wavefront sensor, which is observing the laser beacon. These subsystems drive focus stages, a deformable mirror, a tip/tilt mirror for the incoming starlight, and a tip/tilt mirror for pointing the propagating laser beam. Taken together, and in concert with the rest of the components of the K2 AO system, they provide the tools and the means to observe the universe as never before.

We report on the ongoing VLT Laser Guide Star Facility project, which will allow the ESO UT4 telescope to produce an artificial reference star for the Adaptive Optics systems NAOS-CONICA and SINFONI. A custom developed dye laser producing >10W CW at 589nm is installed on-board of the UT4 telescope, then relayed by means of a single mode optical fiber behind the secondary mirror, where a 500mm diameter lightweight, f/1 launch telescope is projecting the laser beam at 90 km altitude. We described the design tradeoffs and provide some details of the chosen subsystems. This paper is an update including subsystems results, to be read together with our previous paper on LGSF design description.

For the successful operation of laser referenced adaptive optic systems very powerful lasers for the creation of sodium guide stars are necessary. Here we introduce the design of PARSEC, the cw sodium-line laser for the VLT, and present out first laboratory results on the performance of the system. So far we have achieved a stable output power of 12.8W in a single spatial mode and a single frequency.

One of the critical design drivers for the PARSEC laser was that by the time it is integrated into the VLT Laser Guide Star Facility in 2003 it should be able to run remotely without any hands-on tuning for a period of at least one week. In this contribution we describe some of the methods we have employed to achieve this and take a brief look at the proposed operating procedure.

It is foreseen that Extremly large telescope (ELT) will include Adaptive Optics Systems to provide diffraction-limited images in the near infrared. The preliminary atmospheric turbulence properties which affects laser guide star (LGS) generation are presented here. The results of modern model developed in optical communication through atmosphere is used to evaluate LGS size for many different atmospheric situation, with the turbulence intensity concentrate to different heights. This introduce the focusing problem and requirements above the observatory where the adaptive optics system with a reference source will be install. In other case, focus a laser in the mesosphere is impossible in a generic place. In high altitude observatories this is possible, like in canarian observatories. We took 6 experimental turbulence profile to evaluate the beam radius with altitude. A mean value of 0.2 m are found for the diameter of mesospheric volume illuminated by the laser. This is small enough to create an useful LGS for adaptive optics proposes.

We report on our research to develop a fiber Raman laser for multiple sodium laser guide star adaptive optics. Our goal is a fiber laser source at 589 nm with a diffraction-limited continuous-wave output power of at least 10 W and a linewidth of less than 3 GHz. In this paper we present and model our concept of a frequency-doubled fiber Raman amplifier. Recent advances in commercially available pump and seed laser technologies are making the amplifier approach a highly attractive solution for a turn-key sodium-guide star laser system.

The Gemini Laser Launch Telescope will reside behind the secondary support structure of the Gemini 8m telescope, where it will expand an incoming sodium laser beam to 450 mm diameter and launch it into the sky, co-axial to the main telescope. The tight space and stringent performance specifications have required some innovative approaches in optical and mechanical design.

We present the design, laboratory tests and preliminary field tests of a dynamic refocus system for 351nm Rayleigh beacon laser guide stars. The purpose of dynamic refocus is to increase the beacon signal from a pulsed laser, by maintaining focus in a fixed plane while the laser pulse travels through the atmosphere over an extended height range. The focusing element in our system is a moving concave mirror. The optics have been designed and built to focus on a ring of 5 beacons at 1 arc minute radius at the 6.5 m MMT, covering the range 18 through 40 km. Laboratory tests of image quality resulted in 0.5 arcsec refocused images corresponding to the height range 22 through 28 km, free from spherical aberration. Preliminary field tests were performed on the Mt. Bigelow Observatory 1.5 m telescope, with a frequency tripled, Q switched YLF laser beam projected from a 25 cm telescope. To simulate an off axis sub aperture of the MMT, the laser and telescope axes were set 3 m apart and reimaging optics were placed ahead of the refocus unit to image at the same plate scale as the MMT (500 μm/arcsec). Returns from different heights were selected by gating the detector with a Pockels cell. Returns over a 10 km height range from 8km to 18km were brought into focus for a total mirror motion measured to be 900 μm. The system is now ready for testing dynamic refocus, which will be accomplished by attaching the mirror to a metal resonator tuned to the laser pulse frequency. The range from 23 to 35 km to be used will require a motion of 500 μm.

We briefly recall the principle of the polychromatic laser guide star, which aims at providing measurements of the tilt of incoming wavefronts with a 100% sky coverage, We describe the main results of the feasibility study of this concept undertaken within the ELP-OA porgramme. We finally summarize our plans for a full demonstrator at Observatoire de Haute-Provence.

The idea of achieving Adaptive Optics over the majority of the sky using sodium laser guide stars is reaching maturity on Mauna Kea. However, Mauna Kea is a shared astronomical site with 13 institutions and 11 telescopes. Coordination between observatories with laser guide stars and facilities without laser guide stars must be accomplished to prevent sodium light (Rayleigh scatter and the laser guide star itself) from interfering with science observations at the non-laser facilities. To achieve this goal, a technical working group was organized with participation from several Mauna Kea observatories to discuss and agree upon an automated system for avoiding laser “beam” collisions with other telescopes. This paper discussed the implementation of a Laser Traffic Control System (LTCS) for Mauna Kea including a brief history of the coordination effort, technical requirements and details surrounding implementation of laser beam avoidance software, critical configuration parameters, algorithmic approaches, test strategies used during deployment, and recommendations based upon experiences to date for others intending to implement similar systems.

We measured the Rayleigh scattered light from the laser beam launched from Keck II telescope. The illumination at the pupil of Subaru telescope was recorded using the APDs of the Subaru AO system wavefront sensor. Since the field of view of our wavefront sensor is only 5 arcsec in diameter, it was possible to follow the laser beam as it travels across the telescope pupil. The maximum surface brightness of the laser beam is estimated at 16.2 mag/arcsec².

An important requirement for the VLT Laser Guide Star Facility is the ability to measure the centroid height of the atmospheric sodium layer, located at an altitude of about 90km, to an accuracy of 200m. In this paper, we describe the sodium profiler system designed to achieve this and the expected performance.

In the near future several astronomical observatories in Chile are planning to use sodium laser guide stars to increase the sky coverage provided by their adaptive optics facilities. Knowledge of the mesospheric sodium layer behavior is crucial to predict the performance of future laser guide star adaptive optics systems. Whereas the sodium layer has been observed quite extensively at several locations, many of them in the Northern Hemisphere, very little measurements have been made in Chile. The Gemini Observatory therefore initiated a year-long sodium monitoring campaign at the Cerro Tololo Inter-American Observatory located only a few kilometers away from the Gemini South telescope where a conventional laser guide star facility will be offered to the community in 2005, soon to be upgraded to a multi-conjugate adaptive optics system with five laser guide stars. This paper reports on the laser-based sodium monitoring experimental set up and data reduction techniques, and presents some preliminary results on the sodium column density and layer altitude variations observed from February 2001 to February 2002. Implications for the Gemini South Adaptive Optics system expected performance are presented as well.

The realtime knowledge of the altitude and optical characteristics of a generated Laser Guide Star may be necessary for an independent control of the performances of the associated adaptive optics system. For this ourpose a robotic laser guide star monitoring facility, based on a small telescope physically separated from the observatory has been studied, as a subsystem of the VLT LGS project. After reviewing the state of the art on sodium layer dynamical characteristics, we describe the rationale of the project and the main technical choices. Some particular aspects such as differential field motion and laser plume centroiding algorithms are reviewed in detail. The data processing architecture and the associated pipeline is described, and the expected performances are estimated.

An experimental Adaptive Optics system utilizing a low-altitude Rayleigh Laser Guide Star is presented. The current status of the project is described together with plans for future work, with the ultimate goal of providing demonstration Rayleigh LGS AO science on the 4.2m William Herschel Telescope. The implementation of the demonstration system is described in detail as are the technical challenges encountered during the development of the current shared-launch based system. Other papers in this conference describe a proposal for a facility class LGS system for the WHT and the performance of the observatory's NAOMI adaptive optics system.