Adaptive optical

For adaptive optics ro is roughly the spacing of mirror actuators and of wave-front samples required to achieve close to diffraction-limited performance. 

To can be considered as a temporal analogue to the Fried parameter for adaptive optics systems. Another measure used in adaptive optics is the Greenwood frequency. 

Hardy, J.W., Adaptive optics for astronomical telescopes, Oxford University Press, 1998... 

Control Multi-stage, distributed wavefront control phasing, pre-setting, field stabilization, focusing, fine centering, dual conjugates active optics, adaptive optics... 

The OWL optical design is shown in Fig. 1. It is based on a spherical and flat folding secondary mirrors, with a four-element corrector providing for the compensation of spherical and field aberrations as well as advanced active optics and dual-conjugate adaptive optics. A complete discussion would exceed the scope of this report we shall however mention a few key arguments supporting this solution ... 

Low number of surfaces (6) for the complete range of wavefront control functions field stabilization, active focusing and centering, actively deformable surfaces, dual conjugates adaptive optics ... 

Availability of an intermediate focus (after the quaternary mirror) for the calibration of adaptive optics interaction matrices. 

Adaptive optics. atmospheric turbulence, residuals Metrology Wavefront sensor(s)... 

Adaptive optics (AO) undoubtedly constitutes the most daring challenge. It is also absolutely essential seeing-limited observations with a 100-m class telescope would imply impossibly short focal ratio of the instrumentation, and immediate saturation by sky background. A smaller on-sky resolution element is the only way out, which implies at least some degree of adaptive compensation for atmospheric turbulence. 

In conclusion, adaptive optics is the only control system that still requires extensive but not unreasonable technology development. The project is cautiously allocahng more than 10% of its total budget to adaptive optics. Last but not least, an aptly named MAD (Mulh-conjugate Adaptive optics Demonstrator) instrument is currently under construction at ESO to demonstrate the... 

Dierickx, P.,2001, Optical design and adaptive optics properties of the OWL 100-m telescope] ESO Conf. Beyond Conventional Adaptive Optics, Venice, (http //lenin.pd.astro.it/venice2001/proceedings/)... 

Mountain, M., 1996, What is beyond the current generation of ground-based 8-m to 10-m class telescopes and the VLT-17, SPIE 2871, 597 Schumacher, A., Montoya, L., Devaney, N., Dohlen, K., Dierickx, R, 2001, Phasing ELTs for Adaptive Optics preliminary results of a comparison of techniques, ESO Conf. Beyond Conventional Adaptive Optics, Venice (http //lenin.pd.astro.it/venice2001/proceedings/). 

Keywords Micro-optics, MOEMS, multi-object spectroscopy, adaptive optics, astronomi-... 

In the design of MOEMS components, various parameters have to be tuned. These parameters differ according to the functionality of the component. We will consider two different family of devices, programmable slits for Multi-Object Spectroscopy, including Micro-Mirror Arrays (MMA) and Micro-Shutters Arrays (MSA), and Micro-Deformable Mirrors (MDM) for Adaptive Optics systems. 

Micro-Opto-Electro-Mechanical Systems (MOEMS) will be widely integrated in new astronomical instruments for future Extremely Large Telescopes, as well as for existing lOm-class telescopes. The two major applications are programmable slit masks for Multi-Object Spectroscopy (see Ch. 12) and deformable mirrors for Adaptive Optics systems. Eirst prototypes have shown their capabilities. However, big efforts have stiU to be done in order to reach the requirements and to realize reliable devices. 

Zamkotsian, E, Dohlen, K., Buat, V, Burgarella, D., 2000, SPIE 4013, 580 Zamkotsian, E, Dohlen, K., Eerrari, M., 2000b, SPIE 4007, 547 Zamkotsian, E. Dohlen, K., 2001, Conf. Beyond conventional Adaptive Optics Zamkotsian, E, Burgarella, D., Dohlen, K., Buat, V, Eerrari, M., 2001, Proc. 

Figure 1. A ground-based astronomical observatory can be depicted as having four major part telescope, adaptive optics (optional), instmment optics, and the detector.

This chapter will concentrate on the very high quality detectors that are needed in scientific imagers and spectrographs, and other applications that require high sensitivity, such as acquisition and guiding, adaptive optics and interferometry. We limit our discussion to focal plane arrays - large two-dimensional arrays of pixels - as opposed to single pixel detectors (e.g., avalanche photodiodes). 

Limited temporal resolution - Focal plane arrays are aU inherently framing detectors and knowledge of the arrival time of photons is limited to the frame time of the detector. While the frame time can be quite short for adaptive optics detectors ( 1 ms), in most astronomical instruments the frame time is on the order of seconds or minutes, adequate for most astronomical science, but not all. 

Keywords adaptive optics, multiconjugate adaptive optics, extremely large telescopes... 

Another parameter of the turbulence which strongly influences the performance of an adaptive optics (AO) system is the isoplanatic angle. The light... 

Figure 1 outlines the basic AO system. Wavefronts incoming from the telescope are shown to be corrugated implying that they have phase errors. Part of the light is extracted to a wavefront phase sensor (usually referred to as a wavefront sensor, WFS). The wavefront phase is estimated and a wavefront corrector is used to cancel the phase errors by introducing compensating optical paths. The most common wavefront compensator is a deformable mirror. The idea of adaptive optics was first published by Babcock (1953) and shortly after by Linnik (1957). 

Figure 1- Block Diagram of Adaptive Optics system.

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