Preface

Chapter 9 **Point Diffraction Interferometry 187**

Huang and Abeer Al Mohtar

**and Imaging 211**

**VI** Contents

Daodang Wang and Rongguang Liang

Chapter 10 **Interferometry Using Generalized Lock-in Amplifier (G-LIA): A Versatile Approach for Phase-Sensitive Sensing**

Chapter 11 **120° Phase Difference Interference Technology Based on 3 × 3**

Yang Fei, Xu Dan, Cai Haiwen and Qu Ronghui

Aurélien Bruyant, Julien Vaillant, Tzu-Heng Wu, Yunlong Zhu, Yi

**Coupler and its Application in Laser Noise Measurement 233**

The aim of this book is to present readers with the latest progress in optical interferometry. It has descriptions of some of the state-of-the-art interferometry techniques and their applica‐ tions and implications for future research. At present, optical methods of measurements are the most sensitive techniques of noncontact investigations, and at the same time, they are fast as well as accurate which increases reproducibility of observed results. In recent years, the im‐ portance of optical interferometry methods for research has dramatically increased, and appli‐ cations range from precise surface testing to finding extrasolar planets.

The book has a wide variety of topics in interferometry including detailed descriptions of nov‐ el apparatuses and methods, as well as application interferometry for studying biological ob‐ jects, surface qualities, materials characterization, and optical testing. The book consists of eleven chapters. Chapter 1 reviews the techniques for interferogram processing and interpre‐ tation. Chapter 2 presents in situ study of local polymer deformation using Mach-Zehnder in‐ terferometer. Chapter 3 covers two approaches based on optical interferometry for accurate surface inspection. Chapter 4 discusses the application of optical interferometry for characteri‐ zation of thin-film systems. Chapter 5 contains fundamentals of interferometry and its applica‐ tion in investigation of surface shapes. Chapter 6 describes the theory and experimental basis of dynamic speckle interferometry and its application in the investigation of biological ob‐ jects. . Chapter 7 includes basics of fiber-optic interferometry techniques and their applications in sensor fields. Chapter 8 deals with applications of interferometric techniques in all-optical communications networks. Chapter 9 discusses point diffraction interferometer systems for wavefront and surface testing. Chapter 10 covers the method based on generalized lock-in am‐ plifier for extracting phase and amplitude when arbitrary phase modulations are used. The examples of practical implementation of the method are described. Chapter 11 describes 120 degree phase difference technology and its application in laser phase and frequency noise measurement. The book will be interesting for scholars who are exploring theory and experi‐ ment in developing advanced interferometric techniques and their applications.

We would like to thank all the contributors who invested time and shared their expertise in deter‐ mining the scientific merit of the chapters submitted to this book. Our special acknowledgment to the Publishing Process Manager, Ms. Martina Usljebrka, and other staffs of InTech publishing whose constant support and great efforts made this book both possible and successful.

> **Alexander Banishev** University of Illinois at Urbana-Champaign, USA

> **Mithun Bhowmick** University of Illinois at Urbana-Champaign, USA

#### **Jue Wang**

University of Illinois at Urbana-Champaign, USA
