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Optique adaptative et grands télescopes

Abstract : Severely Iimited by atmospheric turbulence, large ground based telescopes are not capable of attaining their intrinsic resolution in a direct manner. At infrared and visible wavelengths, they cannot resolve more details than a telescope with a diametre of several tens of centimetres. The technique of adaptive optics described here, offers the advantage over other techniques, to increase instrumentation resolution, of processing the wavefront before detection, in real time. When photon noise does not prevail, this allows a significant improvement of the signal to noise ratio. The correction is performed by a deformable mirror driven by a control signal calculated from measurements of the wavefront disturbances.The limitations of this instrumentation are Iinked to the number of mirror actuators, the accuracy of the wavefront measurement precision, due to the available flux for this measurement, and the servo loop bandwidth. The error signal sampling rate and the calculation time for the servo loop control determine the resulting bandwidth. We describe here an instrument tested on the sky during Autumn 1989. A wavefront corrected by means of a deformable mirror with 19 actuators permits us to obtain, in real time, diffraction-Iimited images, for wavelengths down to 2.2 um, at the coudé focus of the Observatoire de Haute Provence 1.52 m telescope. A 5x5 subaperture Shack-Hartmann wavefront analyzer is used to measure the disturbances with a frame rate of 100Hz. The resulting servo loop bandwidth is 9 Hz (0 dB point in open loop). The results presented demonstrate the strong potential of this technique for IR imaging in astronomy.
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Submitted on : Friday, July 6, 2012 - 8:34:43 AM
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  • HAL Id : tel-00714946, version 1

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Pierre Kern. Optique adaptative et grands télescopes. Instrumentation et méthodes pour l'astrophysique [astro-ph.IM]. Université Paris-Diderot - Paris VII, 1990. Français. ⟨tel-00714946⟩

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