The use of segmented mirrors in astronomy and adaptive optics is increasing as the ability to measure and control the position of the individual segments to a fraction of the wavelength of light becomes possible. A novel technique is presented in which the relative piston error of adjacent segments is measured using inductive edge-sensors. This technique alleviates the need to have an absolute piston sensor for each of the segment. Modelling of the performance of such a mirror for the case of correcting atmospheric turbulence is presented. This modelling shows that an edge-matched segmented mirror can correct the piston errors in the wavefront even though it does not sense them directly. In addition to this modelling, an experiment. which demonstrates the utility of this technology for adaptive secondary mirrors is described. The results of this experiment, which demonstrates for the first time that an edge-matched mirror can correct for atmospheric piston errors, are presented.

No description available.

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (p. 165-184).

An adaptive optics system consists mainly of a wavefront sensor to detect optical aberrations, a control system to reconstruct the wavefront and compute a correction, and a deformable mirror to apply the correction. In this dissertation, the problem of optimal control of an adaptive optics system is investigated. A direct optimal control approach is used in the controller design. The direct optimal control methodology developed for discrete parameter systems is extended in this study to distributed parameter systems, where the Rayleigh-Ritz method is used for both spatial and temporal variables. The displacement field is written as the product of spatial functions (mode shapes for a vibrating structure, and Zernike modes for deformable mirror) and the generalized coordinates. These generalized coordinates and the control input functions (voltages) are written as simple series expansions in time in terms of selected functions and unknown coefficients. Substitution of these selected functions and their variations into Hamilton's law of varying action results in algebraic equations of motion (AEM) of the structure. These AEM are then considered as the algebraic state equations where the unknown expansion coefficients of the time series (assumed time-modes) for the generalized coordinates are recognized as the states and those of the input functions are recognized as the controls. Using the space-time assumed mode method, the usual variational optimal control problem is transformed into an equivalent algebraic problem. Optimal solutions are then obtained in a closed form and the solution is a global optimum within the time period considered. The solution procedure does not lead to any Ricatti equation or alike. The direct method proved to be simple, computationally efficient, attractive from implementation point of view, and it is general and allows a deterministic modelling of many physical problems. Applied to active vibration control of plates with piezoelectric transducers, the direct methodology exhibits results similar to those obtained through conventional methods. Active shape control of a deformable mirror using the direct approach results in high performance of the controller. The method allows direct control of Zernike modes, and highlights the relationship between the control inputs and Zernike modes through an algebraic controllability measurement index. Robustness of the controller is shown through simulation of smooth and severe random variations of the optical aberrations. In the same line of thought, a space-time finite element method is developed and applied to structural optimal control problems. Finite element method is used for both spatial and temporal discretizations. The unique feature of this method is its ability to analyse the structure-control interaction in the same mathematical framework, which allows simultaneous control and structural model design iterations. However, due to its high dimensionality, the space-time finite element method is computationally less efficient than its counterpart assumed mode. / Graduate

Dissertation (Ph.D. in Astronautical Engineering)--Naval Postgraduate School, March 2009. / Dissertation supervisor: Agrawal, Brij N. "March 2009." Description based on title screen as viewed on April 23, 2009. Author(s) subject terms: Robust control, adaptive optics, segmented mirrors, Shack-Hartmann wavefront sensor, space telescopes, H[infinity], flexible structures. Includes bibliographical references (p. 95-97). Also available in print.

Thesis (Ph. D.)--University of Chicago, Dept. of Astronomy and Astrophysics, December 1997. / Includes bibliographical references. Also available on the Internet.

No description available.

The Pyramid Sensor (PS) is a promising wavefront sensor (WFS) for astronomical adaptive optics (AO) due to its potential to increase the number of accessible scientific targets by more efficiently using guide star (GS) photons. This so-called magnitude gain, as well as the key role played by the PS in several novel multi-reference wavefront sensing schemes have generated intense interest in the device. The diffraction based theory of PS and the underlying optical shop test, the Foucault knife-edge test, is reviewed. The theory is applied to calculate the magnitude gain. The impact of the magnitude gain on the number of galaxies accessible to observation with classical A0 on a TMT sized telescope for the Virgo Cluster Catalogue is assessed via simulations. Additional simulation results are shown to elucidate the impact of various parameters of the pyramidal prism on the magnitude gain. The results of experiments conducted in the UVIC A0 lab with a prototype Id PS are discussed. The Id PS uses a novel optical element called a holographic diffuser to linearize the response of the PS to wavefront tilt. The results of calibrating the sensor are given as well as caveats to the use of such a device. The results of using the Id PS to measure a static aberration as well as spatial and temporal characterization of turbulence produced by the UVIC A0 lab's Hot-Air Turbulence Generator are given.

This thesis describes computer simulations of a new wavefront sensing technique for Adaptive Optics based on local wavefront curvature measurements, along with edge slope measurements. The output signal from the curvature measurements, along with edge slope measurements. The output signal from the curvature sensor can be directly applied to the electrodes of a bimorph or membrane mirror. The mirror is used as an analog device to solve the Poisson Equation, providing a fast real time compensation for atmospheric disturbances. The open loop characteristics of the system are presented. The ideal response is analyzed, and side effects such as non-linearity, photon and diffraction noises are discussed. Closed loop simulations are presented thereafter. A seven actuator system showed a few unstable modes. A 13 actuator system with proper filtering corrects the atmospheric perturbations. To simulate atmospheric distorted wavefronts, an algorithm based on spectral decomposition of the Zernike covariance matrix was derived. This sensor can also be used to test large telescope mirrors using a modified program that solves the Poisson Equation with Neumann boundary conditions.

Thesis (Ph. D.)--University of Chicago, Department of astronomy and astrophysics, December 1999. / Includes bibliographical references. Also available on the Internet.