Fritz Merkle

First diffraction-limited astronomical images with adaptive optics

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.

Synthetic-aperture imaging with the European Very Large Telescope

The European Southern Observatory Very Large Telescope is a project for a linear array of four independent 8-m telescopes. This concept offers the possibility of operating the telescopes in the synthetic-aperture mode as an interferometer with a maximum baseline of approximately 112 m. The first target for the interferometric operation is phasing in the infrared range, with a gradual expansion toward shorter wavelengths. Two smaller movable telescopes are added to the linear array for a complete filling of the spatial-frequency plane. Adaptive optics is applied for a real-time phase compensation of the individual pupils for atmospheric distortions. The whole array, in addition to the individual pupils of the independently mounted telescopes, must be phased, including pupil position corrections due to pupil foreshortening and shift effects, in order to reach a reasonable phased field of view.

Adaptive optics prototype system for infrared astronomy: I. System description

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).

Come-on-plus project: an upgrade of the come-on adaptive optics prototype system

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).

Latest developments of active optics of the ESO NTT and the implications for the ESO VLT

The latest developments of active optics of the ESO NTT include the reduction of friction in the lateral supports of the primary mirror and in the positioning system of the secondary mirror. The most important remaining problem is the local air condition. The implications for the ESO VLT and the latest developments in the design of its active optics are discussed.

Come-On: An Adaptive Optics Prototype Dedicated To Infrared Astronomy.

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.

Application Of Adaptive Optics To Astronomy

Adaptive optical systems and their applications in astronomy have been discussed for over a decade. Meanwhile the main components like deformable mirrors, wavefront sensors etc. for these real time correction systems of atmospheric turbulence effects, are commercially available. The principles of of this technology, its predicted performance and the current programs underway to implement adaptive optics for astronomical purposes are summarized.

Adaptive Optics for Large Telescopes

The performance of large telescopes is determined both by their angular resolution and by their collection area. It is, therefore, important to achieve as high an angular resolution as possible by site selection, by avoiding image deterioration by the telescope and its environment, and by real time image restoration by adaptive optics. We summarize the principles of adaptive optics, their predicted performance and the current programs underway to implement adaptive optics for astronomical purposes.

The Interferometric Mode of the European Very Large Telescope

The European Very Large Telescope program has been approved in 1987. It aims to consists of an array of four 8 m telescopes, plus two additional 2 m class auxiliary telescopes, the latter being fully dedicated to optical (infrared and visible) interferometry, with possible combination of some and, in the long term, all large telescopes. We discuss the implementation of this program in the next ten years.

Adaptive Optics For The European Very Large Telescope (VLT)

The linear array concept for ESOs Very Large Telescope (VLT) project opens the possibility of observations with very high angular resolution. Realistic target for an interferometric operation is the infrared range from 5 to 20μm and later a gradual expansion to shorter wavelengths. In the interferometric mode the gain of the 8-meter diameter single apertures of the VLT is only given if adaptive optics is applied for a real-time partial or full phase compensation of the degradations due to atmospheric turbulences.