Adaptive optics engineering handbook : [Recurso electrónico] / edición, Robert K. Tyson.

Incluye referencias bibliográficas e índice.

From the Series Editor.--

Preface.--

Contributors.--

1. Introduction (Robert K. Tyson).--
2. System Design and Optimization (Ronald R.Parenti).--
3. Guide Star System Considerations (Richard J.Sasiela John D.Shelton).--
4. Wavefront Sensors (Joseph M.Geary).--
5. Deformable Mirror Wavefront Correctors (Ralph E.Aldrich).--
6. Innovative Wavefront Estimators for Zonal Adaptive Optics Systems (Walter J.Wild).--
7. Micromachined Membrane Deformable Mirrors (Gleb Vdovin).--
8. Surface Micromachined Deformable Mirrors (William D.Cowan Victor M.Bright).--
9. Liquid Crystal Adaptive Optics (Gordon D.Love).--
10. Wavefront Sensing and Compensation for the Human Eye (David R.Williams Junzhong Liang Donald T. Miller Austin Roorda).--
11. Wide Field-of-View Wavefront Sensing (Erez N.Ribak).--
Index.

Introduction (Robert K.Tyson) :

Adaptive optics are used to enhance the capability of optical systems by actively compensating for aberrations. These aberrations, such as atmospheric turbulence,optical fabrication errors, thermally induced distortions, or laser device aberrations, reduce the peak intensity and smear an image or a laser beam propagating to a target. Normally, increasing the aperture size decreases the diffraction angle and makes an image sharper. However, for many optical systems,the beam or image quality is limited, not by the aperture, but by the propagation medium.

The twinkling of stars or distorted images across a paved road on a hot summer day is caused by turbulence in the atmosphere. Distortions like these can be corrected by adaptive optics. The result of more than three decades of technology development, adaptive optics systems are being used at observatories around the world. This Handbook is a guide to the implementation of adaptive optics, a collection of analysis tools for system design and development, and an introduction to up-to-date developments in the multidisciplinary adaptive optics field.

The principal uses for adaptive optics are improving image quality in optical and infrared astronomical telescopes, imaging and tracking rapidly moving space objects, and compensating for laser beam distortion through the atmosphere.Although these missions differ, the techniques used to compensate for the underlying distortions are similar.

Adaptive optics are real-time distortion-compensating systems. Although many types of adaptive optics systems have been tried in the laboratory or field,the most common adaptive optics system in use today consists of three subsystems. A wave-front sensor measures the distortion induced by the atmosphere by evaluating the light from a natural source or an artificial beacon placed high above the telescope. An active mirror, called a deformable mirror, can rapidly change its surface shape to match the phase distortions measured by the wavefront sensor. A control computer is used to evaluate the wavefront sensor measurements and translate the signals into control signals to drive the actuators of the deformable mirror. Over large apertures, like those used in modern astronomical telescopes,the wavefront tilt is a dominant effect which, as it varies rapidly during the exposure time, further distorts the image. Adaptive optics systems often offload the tilt wavefront measurement to a specialized tilt control mirror to remove the large stroke requirements from the deformable mirror.

Because the adaptive optics compensation is performed by macroscopic movement of an optical element, the system is called inertial. Because the compensation is linearly proportional to the disturbance, the system is considered linear. These terms are in contrast to nonlinear phase conjugation techniques which employ atomic or molecular changes in optical materials and exploit their nonlinear phase compensation properties. Nonlinear systems are discussed elsewhere in the literature and will not be a topic of discussion in this practical examination of adaptive optics.

There are innovative variations on the standard design. For example, the 6.5-m Smithsonian Institution-University of Arizona Monolithic Mirror Telescope located at the Steward Observatory in Arizona will put the deformable mirror on the Cassegrain secondary mirror surface instead of using the separate deformable mirror.

In astronomy, adaptive optics provide the means for increasing the angular resolution in direct imaging, and they provide higher performance for many spectroscopic, interferometric and photometric measurements. For example, if the scientific goal is to make a simple detection of a faint point source such as a star in the presence of a bright sky background, the final detected signal-to-noise ratio is proportional to D/α, where D is the aperture diameter of the telescope’s primary mirror and α is the angular resolution at the time of detection. Large telescopes now have apertures up to 10 meters, today’s practical engineering limit. From the above ratio, decreasing a is just as important as increasing D. Adaptive optics provides the opportunity to decrease a to the theoretical limit.

Área de Ciencias Básicas e Ingenierías

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