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A compact, solid state, zenith looking 94 GHz meteorological radar is described. Samples of the reflectivity data obtained from representative samples of hydrometeors, including cirrus cloud and fog, are presented. This bistatic FMCW radar delivers continuous information on the distribution and thickness of cloud layers, permitting accurate determination of the cloud base altitude and upper limit. The maximum range is 16 km, with a corresponding resolution of 30 m: both range and averaging time are user selectable in ranges 2-16 km and 5-60 s respectively. A radiated millimetre wave power of below 200 mW yields a dynamic range of over 60 dB in the received signal.

Since many years CILAS developed active mirrors for synchrotron radiation beamlines. The paper presents the recent developments of bimorph structures usable for x ray mirrors, monochromator crystals, and gratings. The adaptation of the structure to the 3 applications above mentioned is done by choosing the upperplate material and surface coating. The bimorph structure is designed to produce a simple spherical bending of the active plate, or more sophisticated shapes as ellipsoids or parabola. The bimorph structure can be delivered in a mechanical housing able to properly support it. High voltage amplifiers with digital input fitted to control the shape as well as a curvature measurements system may be delivered providing the possibility of closed loop operation. Standard versions of bimorph mirrors and gratings are available. Most of the development works was done under ESRF support.

Since approximately 5 years, several experimental Adaptive Optics Systems have been tested on different astronomical sites. This paper describes a general purpose AOS designed for new or existing telescopes for diameters ranging from 2 to 4 meters. Investigations on actually available Adaptive Mirrors and Wavefront sensors are made. The use of a bimorph mirror and simplified Shack Hartmann is proposed. Results of simulation to evaluate the Strehl ratios for different wavelengths are given versus seeing conditions and star magnitudes. This leads to the conclusion that low cost, turn key AOS are a new attractive possibility for Astronomy.

The problem to be solved is to maintain the best efficiency of an Adaptive Optics System (AOS) during an observing run, versus different seeing conditions and star magnitudes. The paper uses the modal control and partial correction concepts as defined in previous works. It has been demonstrated in these works that the Strehl ratio of images corrected by an AOS can be evaluated by a simple criteria. Such a criteria uses only the temporal covariance of the controls applied to the AO mirror. Using these different results a method to optimize the loop gains is suggested. This method can be applied during real time run of the AOS. It uses the only knowledge of the modal control values applied to the AO mirror and the knowledge of the residual wavefront errors as measured by the wavefront sensor.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The COME-ON+ adaptive optics system was set up on the ESO 3.6-meter telescope for two technical runs (in December 1992 and April 1993) and is now routinely used for astronomical observations. This system is an upgrade of the COME-ON adaptive optics prototype system. During the technical runs, images were recorded in the V, I, J, K and L' spectral bands. Currently, the best resolution obtained is 0.1' in H (1.65 micrometers ) under bad seeing conditions (seeing > 1' and averaged wind speed > 10 m/s) and reference star magnitudes of 6 to 8. The corresponding Strehl ratio is 35%. 70% Strehl ratio was obtained at 2.2 micrometers (K band). At 0.9 micrometers (I band), in the partial correction regime, the resolution is of the order of 0.2' for 0.8' seeing and 10 m/s averaged wind speed. The optimized modal control has been used on faint reference stars. The limiting magnitude (in V band) for wavefront sensing has been measured to 14 and 15 depending on the spectral type of the reference star and the seeing conditions for a low frequency tip-tilt correction.

LASERDOT has acquired a wide experience in Adaptive Optics Systems: components and hardware manufacturing, dedicated software, system integration and maintenance. Associated with several research organizations, it has taken advantage of having installed the first AO systems routinely used by astronomers. This paper presents deformable mirrors as well as tip- tilt mirror designed and achieved at Laserdot jointly with Observatoire de Paris-Meudon. Some comparisons between the different types of deformable mirrors are done.

The design of an Adaptive Optics System must take into account at least the following main criterias. First, correction efficiencies versus the atmospherical turbulences, i.e., the Fried diameter and the turbulence power spectrum. Second, sky coverage versus star magnitudes and star classes. To answer these criteria an optimization method is defined. It uses as main parameter the residual mean phase errors of the corrected wavefronts. It is demonstrated that this parameter able us to optimize the System performances: number of modes to be controlled, sampling rates of phase measurements, and noise minimization. Finally an application is done for a 3.6 m class telescope and 2 different adaptive mirror types.

The paper defines the concept of optimized modal correction for adaptive optics systems. The objective is to achieve the best image quality versus the disturbances to be corrected and the level of light coming from the observed object. Examples of optimized modal correction effects on optical transfer functions are given and compared to the results obtained without optimization. This work has been supported by DRET (Direction des Recherches, Etudes et Techniques) and CFH Corp. (Canada France Hawaii Corp.).

Following the successful astronomical runs of the Come-On adaptive optics prototype on the ESO 3.6 m telescope in La Silla, Chile an upgraded version called Come-On-Plus is currently being constructed and was set up in December 1992. This paper describes the main improvements of this new system. In particular, the 52 actuator deformable mirror with 30 Hz closed loop bandwidth, the modal control, the high detectivity wavefront sensor channel, and the infrared imaging channel are presented. Finally, the laboratory tests of each subsystem are analyzed. This second prototype is dedicated to routine astronomical observing as well as providing design parameters for the adaptive optics for the ESO Very Large Telescope (VLT).

Adaptive optics systems have proven their efficiency for obtaining high resolution images in the field of large astronomical telescopes. The same techniques can be applied to correct x-ray mirror shapes. The paper describes the principle of an adaptive x-ray mirror system (mirror architecture, measurement subassembly, control unit). In the second part, first results obtained during the design study of the ESRF adaptive x-ray mirror are given. The possibility of achieving cylindrical or elliptical mirror surfaces using adaptive optics techniques are suggested.

Over the past two years, laserdot has developed a new machine vision system for obstacle detection by mobile robots. A pulsed laser illuminates the road in a zone from 100 to 150 meters in front of the vehicle and the backscatter is analyzed by a linear array of photodetectors connected to a computer. Each obstacle is detected and its position is determined. The distance is calculated by measuring the pulse time-of-flight, producing a complete three-dimensional image without scanning. The system was jeep-mounted for testing in a military environment at the Angers Technical Center (ETAS) in France. This article describes the laserdot vision system and its design features, as well as the test results from ETAS. The system is capable of providing information on the shape of the road in front of the vehicle, including slope and banking measurements. Lastly, the future integration of the detector in a mobile robot is detailed. These works have been supported by Direction des Recherches, Etudes et Techniques (DRET).© (1992) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Laserdot has been working on adaptive optics systems for over 15 years. The first applications were about laser beam control. This has led to the first kind of deformable mirrors we use for the correction and dithering of the wavefront. These mirrors may be cooled depending on the laser beam power. Lately, with the participation of different European institutions, this knowledge has been applied to astronomical imaging. The `Come On' project showed how interesting such a technique is. `Come On Plus,' the project to be carried out, will certainly improve these first results. At the same time, jointly with Francois Roddier and for astronomical purposes too, Laserdot has achieved some bimorph mirrors which are to be used with a curvature sensor. This paper aims to oversee the mechanical components which have been designed for these different studies.

This paper reports the results of the observations made with the VLT Adaptive Optics Prototype System 'COME-ON' at the ESO 3.6 meter telescope. The analysis of uncorrected and corrected images in the near-IR wavelength range (below 5 microns) leads to a detailed assessment of the system performance in terms of improvement of angular resolution that nearly achieves the ideal diffraction profiles down to 1.7 micron wavelength, as well as a Strehl ratio approaching 0.6-0.8 at 3.8 microns. A resolution of 0.12 arcsec has been obtained with this system at 1.7 microns which is wavelength-dependent on the temporal parameters of the observation. The current limiting magnitude for the reference source is m sub R = 11.5 when applying the full correction capabilities of the system, and m sub R = 13 if only the wavefront tilt is corrected.

This paper is a presentation of the Come-On-Plus adaptive optics system, based on the Come-On prototype. Come-On-PIus will be set up in 1992 on the ESO 3.6 m telescope in La Silla (Chile). It is an upgrade of the Come-On instrument, with a 52 actuator deformable mirror, and 30 Hz correction bandwidth. But the main improvement concerns the wavefront sensing, designed in this instrument for astronomical applications, with a high detectivity wavefront sensor and a specific mirror control algorithm. This system is planned for routine astronomical observing as well as providing design parameters for the adaptive optics system of the ESO Very Large Telescope (VLT).

In a preceding paper the authors calculated the mean value of the Optical Transfer Function (OTF) for a high-resolution imaging instrument corrected by adaptive optics. The Come_On experiments carried out during 1990 show good correlation with the mathematical model. In the present paper the model described in the 1987 paper is revised to introduce modal control and take into account the effects of time lags and/or angular depointings on the corrected OTF. These lags represent the time needed to perform the computations between phase measurements and corrections, and the angular depointings define the angular field where the corrections are valuable. The model permits an evaluation of the OTF decay in respect to the Fried diameter. Numerical results are given using the modified model with the Come_On project specifications. These works have been sponsored by the French Defense Ministry through the Direction des Recherches, Etudes et Techniques (DRET).

This paper is a presentation of the so-called COME-ON adaptive optics prototype system developed jointly by four European institutions. This system has been tested on the 1.52m telescope of the Observatoire de Haute Provence on October 12 to 23 and November 13 to 24, 1989. Diffration-limited infrared imaging has been achieved during these first tests. The adaptive optics system consists of a 19 actuator deformable mirror and a Hartmann-Shack type wavefront sensor. In this instrument the wavefront sensing is performed at visible wavelengths while the correction is performed for near infrared imaging (1 .2 to 5 .tm). Specialized computers drive the deformable mirror and a tip-tilt mirror. The bandwidth of the servo-loop is 9 Hz at 0 dB point in open-loop. The results obtained with this instrument will be very useful for the design of the future adaptive optics system for the ESO Very Large Telescope (VLT).

An adaptive optics system is considered as a multi loops servo system. The main components of the ioops are: - the wavefront sensor, - the real time digital processor, - the adaptive mirror and the high voltage control amplifiers. These loops are closed via the wavefront itself. Generally the detector of the wavefront sensor is a CCD camera. At first, images of the CCD matrix are digitized and the processor computes the local slopes of the wavefront ; secondly, the processor performs the calculation needed to output the values of the controls. Finally data are sended to the adaptive mirror through a digital/analog converter and the power amplifiers. A scheme of the loops is given where each major constituent is replaced by its transfer function. The time lags due to the CCD matrix and calculations are expressed. Using the Nichols criterion which defines the stability of the loops, the effects of the sampling rate and time lags on gain and bandwidth are studied. The results of a numerical model are given and comparisons are made with the COME-ON experiments. Same paper has been presented during the SPIE's 1990 Symposium on Astronomical Telescopes and Instrumentation for the 21St Century in February 1990.© (1990) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

An adaptive optics prototype system has been tested at the 1.52 m telescope of the Observatoire de Haute Provence, resulting in diffraction-limited images at near infrared wavelengths (2.2 to 5 microns). This paper presents the first results and a short analysis, which demonstrate the considerable gain in resolution and sensitivity achieved by this technique. Single stars, close binary stars, and a satellite have been resolved. In some cases another star several arcseconds apart has been used as reference for the wavefront sensing.

The paper presents the status of the COME-ON (C GE Observatoire de Meudon ESO ONERA) experiment. This instrument, developed and tested by several European laboratories, is an adaptive optical system with a 19 actuators deformable mirror and a Hartmann Shack type wavefront sensor. The wavefront sensing is performing at visible wavelengths; a special computer drives the deformable mirror which should achieve diffraction limited infrared imagery with large optical telescope. The different components and their individual characteristics are described. The results of the tests of some components are given: 19 actuators deformable mirror, tip-tilt mirror. The expected performances are summarized and possible applications of the instrument to astronomical sources are presented. The isoplanaticity aspect, the required temporal bandwidth and reference source brightness is discussed. The conclusions of the experiment will be used for the design of adaptive optics for the ESO Very Large Telescope.

Most of the adaptive optics experimented for astronomy uses a Shack-Hartmann wavefront sensor. By their principle these sensors require a large amount of real time calculations. The time spent to perform these calculations may become a limiting factor of the bandwidth. It should be probably the case for the mirrors with high numbers of actuators which will be built for the very large telescope projects. Recently, F. Roddier has proposed an analog curvature sensing method which could theoritically avoid any calculations. We will demonstrate that optical filterings which transform wavefront distorsions in intensity modulations can be used with a reasonable amount of calculations to perform the control of an adaptive optical system. Some of these filtering which permits differential measurements offers the possibility to eliminate the inexpected speckle intensity modulations.

High resolution imaging in ground-based astronomy is limited by the wave front degradation through the turbulent atmosphere. Adaptive optics offers the possibility to overcome these limitations. It employs a real-time phase compensation with a phase shifting optical element, which is usually a deformable mirror. The information for the control of the mirror surface is gained from a wavefront sensor. Thispaper describes an adaptive optics prototype for infrared imaging using a visible wavefront sensor and its expected performances in astronomy.