Optical Methods of Measurement

Wholefield Techniques, Second Edition

Rajpal Sirohi

• Publisher: CRC Press
• Year: 2018
• Print ISBN: 9781574446975
• eBook ISBN: 9781351837248
• Topic: Technology & Engineering
• Subtopic: Optics & Light
• Index: Technology & Engineering

Optical Methods of Measurement: Wholefield Techniques, Second Edition provides a comprehensive collection of wholefield optical measurement techniques for engineering applications. Along with the reorganization of contents, this edition includes a new chapter on optical interference, new material on nondiffracting and singular beams and their applications, and updated bibliography and additional reading sections.

The book explores the propagation of laser beams, metrological applications of phase-singular beams, various detectors such as CCD and CMOS devices, and recording materials. It also covers interference, diffraction, and digital fringe pattern measurement techniques, with special emphasis on phase measurement interferometry and algorithms. The remainder of the book focuses on theory, experimental arrangements, and applications of wholefield techniques. The author discusses digital hologram interferometry, digital speckle photography, digital speckle pattern interferometry, Talbot interferometry, and holophotoelasticity.

This updated book compiles the major wholefield methods of measurement in one volume. It provides a solid understanding of the techniques by describing the physics behind them. In addition, the examples given illustrate how the techniques solve measurement problems.

1 Waves and Beams

Optics pertains to the generation, amplification, propagation, detection, modification, and modulation of light. Light is considered a very tiny portion of the electromagnetic spectrum responsible for vision. In short, optics is science, technology, and engineering with light. Measurement techniques based on light fall into the subject of optical metrology. Thus, optical metrology comprises varieties of measurement techniques, including dimensional measurements, measurement of process variables, and measurement of electrical quantities such as current and voltages.

Optical methods are noncontact and noninvasive. Indeed, the light does interact with the measurand, but does not influence its value in the majority of cases, and hence such measurements are termed noncontact. Further, information about the whole object can be obtained simultaneously, thereby giving optical methods the capability of wholefield measurement. The measurements are not influenced by electromagnetic fields. Further, light wavelength is a measurement stick in length metrology, and hence high accuracy in measurement of length/displacement is attained. Some of these attributes make optical methods indispensable for several different kinds of measurements.

1.1 THE WAVE EQUATION

Light is an electromagnetic wave, and therefore satisfies the wave equation

${\nabla }^{2}E\left(r,t\right)-\frac{1}{c^2}\frac{{\partial }^{2}E\left(r,t\right)}{\partial t^2}=0$

(1.1)

where E(r, t) is the instantaneous electric field of the light wave and c is the velocity of light. [The instantaneous magnetic field of the wave, B(r, t), satisfies a similar equation.] Equation 1.1 is a vector wave equation. We are interested in those of its solutions that represent monochromatic waves, that is,

$E\left(r,t\right)=E\left(r\right)\exp \left(-i\text{ω}t\right)$

(1.2)

where E(r) is the amplitude and ω is the circular frequency of the wave. Substituting Equation 1.2 into Equation 1.1 leads to

${\nabla }^{2}E\left(r\right)+k^{2}E\left(r\right)=0$

(1.3)

where k² = ω²/c². This is the well-known Helmholtz equation. A solution of the Helmholtz equation for E(r) will provide a monochromatic solution of the wave equation.

1.2 PLANE WAVES

There are several solutions of the wave equation; one of these is of the form

$E\left(r\right)=E_0\exp \left(ik\cdot r\right)$

(1.4)

This represents a plane wave, which has constant amplitude E₀ and is of infinite cross-section. A plane monochromat...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• From the Series Editor
• Preface
• Preface to First Edition
• Author
• Chapter 1 Waves and Beams
• Chapter 2 Optical Interference
• Chapter 3 Diffraction
• Chapter 4 Phase-Evaluation Methods
• Chapter 5 Detectors and Recording Materials
• Chapter 6 Holographic Interferometry
• Chapter 7 Speckle Metrology
• Chapter 8 Photoelasticity
• Chapter 9 The Moiré Phenomenon
• Index