Chapter 1. Image Stabilization

1.1 Introduction

1.2 Wavefronts

1.3 Wavefronts and Optical Systems

1.4 Beam Wander

1.5 Image Jitter

1.6 Beam Wander versus Image Jitter

Chapter 2 Effects of Turbulence on a Wavefront

2.1 Introduction

2.2 Effect of the Atmosphere

2.3 Description of a Wavefront

2.4 Angle of Arrival Fluctuations

2.5 Higher Order Modes

2.6 Global Tip and Tilt

2.7 Effect of the Atmosphere on Intensity at a Receiver

Chapter 3 Wavefront Sensors

3.1 Introduction

3.2 Transforming Optical Path Length Differences into Intensity Variations

3.3 Interferometery

3.3.1 Mach Zhender Interferometer

3.3.2 Shearing Interferometer

3.3.3 Ronchigrams

3.4 Phase Contrast

3.4.1 Foucault Knife Edge Test

3.4.2 Phase Diversity Sensors

3.5 Local Slope Measurements

3.5.1 Babcock Detector

3.5.2 Pyramid Sensor

3.5.3 Shack-Hartmann Sensor

Chapter 4 Low Order Wavefront Compensation

4.1 Introduction

4.2 Wavefront Compensation

4.3 Wavefront Correctors for Piston, Tip and Tilt

4.3.1 Mirror Correctors

4.3.2 Optically Powered Correctors

4.4 Use of Tilt Correctors in Laser Guide Stars

4.5 Mechanical Operation of Tilt Stages

Chapter 5 Image Stabilization Systems Simplified

5.1 Introduction

5.2 Integrating Sensor and Compensator

5.3 System Control

5.4 Model Image Stabilizer

5.4.1 Light Source

5.4.2 Wavefront Sensor

5.4.3 Wavefront Compensator

5.4.4 Control System

5.5 Information Flow for Image Stabilization

5.6 Types of Controllers

Chapter 6 Performance

6.1 Introduction

6.2 Image Structure

6.3 Strehl Ratio

6.4 Performance Evaluation

Chapter 7 Image Stabilization Systems

7.1 Introduction

7.2 Astronomical Imaging Tip-Tilt Systems

7.3 Programs using Image Stabilization Systems

7.4 Beam Steering for Interferometers

7.5 Stabilized Long Baseline Interferometers

Chapter 8 Alternative Approaches

8.1 Introduction

8.2 Liquid Crystal Spatial Light Modulators

8.3 Orthogonal Transfer Charge Coupled Devices

8.4 Micro-electrical Mechanical Devices

Chapter 9 Bibliography

Preface

This volume of the SPIE Tutorial Text explores the fundamental aspects of image stabilization in optical systems used for astronomy and optical communication systems. The material is presented with few assumptions about the reader's previous experience in the field and should be accessible to most interested readers.

Chapter 1 serves as an introduction to wavefronts, optical systems, and the challenges surrounding image stabilization. Chapter 2 provides an overview of the effects of atmospheric turbulence on a wavefront and Chapters 3 and 4 discuss how to sense and minimize these effects, respectively. In Chapter 5, the devices introduced in the previous two chapters are combined into an image-stabilization system, with Chapter 6 discussing key performance issues of such systems. Chapter 7 provides a brief survey of existing image-stabilization systems. Chapter 8 describes several alternative approaches to image stabilization that, while less common, can also be effective.

Complete coverage of all possible approaches and methods available for image stabilization is not possible in an introductory text, so the authors have focused on the most commonly encountered approaches. Also, many of the subtleties of advanced image-stabilization systems have been left for the interested reader to explore on his/her own. Many useful reference texts and articles are provided in Chapter 9.

Scott Teare
Sergio Restaino
May 2006