Electro optics handbook 2e waynant, ediger

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HANDBOOK

Food and Drug Administration

Sydney Tokyo Toronto

Library of Congress Cataloging-in-Publication Data

Electro-optics handbook / Ronald W Waynant, editor, Marwood N Ediger, editor.—2nd ed.

Includes bibliographical references and index.

ISBN 0-07-068716-1 (hc)

1 Electrooptical devices—Handbooks, manuals, etc I Waynant, Ronald W.

II Ediger, Marwood N., date.

621.36—dc21

99-044081

Copyright  2000 by The McGraw-Hill Companies, Inc All rights reserved.

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retrieval system, without the prior written permission of the publisher.

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ISBN 0-07-068716-1

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CONTRIBUTORS

Georg F Albrecht,Lawrence Livermore National Laboratory, Livermore, California (CHAP 5)

John E Bowers,University of California at Santa Barbara (CHAP 29)

George R Carruthers,E O Hulburt Center for Space Research, Naval Research Laboratory, ington, D.C (CHAP 15)

Wash-Y J Chen,Department of Electrical Engineering, University of Maryland, College Park, Maryland

( CHAP 22)

James J Coleman,Microelectronics Laboratory, University of Illinois, Urbana, Illinois (CHAP 6)

Charles M Davis,Centerville, Virginia (CHAP 21)

J G Eden,Department of Electrical Engineering, University of Illinois, Champaign, Illinois (CHAP 20)

Marwood N Ediger,Food and Drug Administration, Rockville, Maryland (CHAP 1)

T J Harris,Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland (CHAP 11)

Masamitsu Haruna,Department of Electronic Engineering, Osaka University, Osaka, Japan (CHAP 26)

P.-T Ho,Joint Program for Advanced Electronic Materials, Department of Electrical Engineering, versity of Maryland, College Park, Maryland (CHAPS 9, 22)

Uni-Michael Ivanco,Atomic Energy of Canada Limited, Chalk River Laboratories, Chalk River, Ontario

Beth A Koelbl,Nulight, Virginia Station, Virginia (CHAP 28)

Chi H Lee,Joint Program for Advanced Electronic Materials, Department of Electrical Engineering, University of Maryland, College Park, Maryland (CHAP 9)

Thomas Liljeberg,University of California at Santa Barbara (CHAP 29)

James T Luxon,Associate Dean, Graduate Studies, Extension Services and Research, GMI Engineering and Management Institute, Flint, Michigan (CHAP 25)

Sharon Miller,Food and Drug Administration, Rockville, Maryland (CHAP 2)

Hiroshi Nishihara,Department of Electronic Engineering, Osaka University, Osaka, Japan (CHAP 26)

John A Pasour,Mission Research Corporation, Newington, Virginia (CHAP 8)

Stephen A Payne,Lawrence Livermore National Laboratory, Livermore, California (CHAP 5)

G Rodriguez,Everitt Laboratory, University of Illinois, Urbana, Illinois (CHAP 20)

Frederick A Rosell,Westinghouse Electric Corporation, Defense and Space Center, Baltimore, land (CHAP 18)

Mary-Roland Sauerbrey,Department of Electrical and Computer Engineering and Rice Quantum Institute, Rice University, Houston, Texas (CHAP 3)

William T Silfvast,Center for Research in Electro-Optics and Lasers, Orlando, Florida (CHAP 4)

Edward J Sharp, Department of the Army, U.S Army Research Laboratory, Fort Belvoir, Virginia

( CHAP 13)

David H Sliney, Department of the Army, U.S Army Environmental Hygiene Agency, Edgewood, Maryland (CHAP 23)

Suzanne C Stotlar,Yorba Linda, California (CHAPS 16, 17)

Toshiaki Suhara,Department of Electronic Engineering, Osaka University, Osaka, Japan (CHAP 26)

M E Thomas,Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland (CHAP 11)

W J Tropf,Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland (CHAP 11)

Carlton M Truesdale,Corning Industries, Corning, New York (CHAP 12)

M J C van Gemert,College of Engineering, The University of Texas at Austin, Austin, Texas (CHAP.

24)

Osamu Wada,Deputy Manager, Fujitsu Laboratires, Limited, Optical Semiconductor Devices ratories, Atsugi Kanagawa, Japan (CHAP 27)

Labo-Ronald W Waynant,Food and Drug Administration, Rockville, Maryland (CHAP 1)

Ashley J Welch,College of Engineering, The University of Texas at Austin, Austin, Texas (CHAP 24)

Gary L Wood,Director, Center for Night Vision and Electro-Optics, Department of the Army, U.S Army Research Laboratory, Fort Belvoir, Virginia (CHAPS 13, 14)

Li Yan,Department of Electrical Engineering, University of Maryland, Baltimore, Maryland (CHAP 9)

Clarence J Zarobila,Optical Technologies, Incorporated, Herndon, Virginia (CHAP 21)

McGraw-Hill Optical and Electro-Optical Engineering Series Robert E Fischer and Warren J Smith, Series Editors

Published

Hecht•THE LASER GUIDEBOOK

Melzer & Moffitt•HEAD MOUNTED DISPLAYS

Miller & Friedman•PHOTONICS RULES OF THUMB

Mouroulis•VISUAL INSTRUMENTATION

Smith•MODERN OPTICAL ENGINEERING

Smith•MODERN LENS DESIGN

Smith•PRACTICAL OPTICAL SYSTEM LAYOUT

Waynant & Ediger•ELECTRO-OPTICS HANDBOOK

Wyatt•ELECTRO-OPTICAL SYSTEM DESIGN

Other Books of Interest

Optical Society of America•HANDBOOK OF OPTICS,SECOND EDITION,VOLUMES I,II

Keiser•OPTICAL FIBER COMMUNICATIONS

Syms, Cozens•OPTICAL WAVES AND DEVICES

Chomycz•FIBER OPTICAL INSTALLATIONS

ABOUT THE EDITORS

R ONALD W W AYNANTis Editor in Chief of IEEE Circuits and Devices

Maga-zine and senior optical engineer at the Food and Drug Administration’s

Elec-tro-Optical Branch He also gathered the distinguished contributors for and

edited the first edition of this Handbook He resides in Clarksville, Maryland.

M ARWOOD N E DIGER has over 12 years’ experience in the use of lasers in medical applications Marwood lives in Vienna, Virginia.

CONTENTS

Contributors xv

Preface to Second Edition xvii

Preface to First Edition xix

2.4 Measurements and Calibration / 2.10

2.5 Sources of Noncoherent Optical Radiation / 2.21

2.6 References / 2.35

Chapter 3 Ultraviolet, Vacuum-Ultraviolet, and X-Ray Lasers

3.1 Lasers in the Electromagnetic Spectrum / 3.1

3.2 Principles of Short-Wavelength Laser Operation / 3.4

3.3 Ultraviolet and Vacuum Ultraviolet Lasers / 3.11

3.4 X-Ray Lasers and Gamma-Ray Lasers / 3.36

3.5 References / 3.43

viii CONTENTS

4.1 Introduction / 4.1

4.2 Visible Lasers in Gaseous Media / 4.2

4.3 Visible Lasers In Liquid Media—Organic Dye Lasers / 4.14

4.4 Visible Lasers in Solid Materials / 4.18

4.5 References / 4.21

Chapter 5 Solid-State Lasers Georg F Albrecht and Stephen A Payne 5.1

5.1 Introduction / 5.1

5.2 Solid-State Laser Devices / 5.2

5.3 Solid-State Laser Materials / 5.34

5.4 Future Directions / 5.56

5.5 References / 5.57

6.1 Compound Semiconductors and Alloys / 6.1

6.2 Energy Band Structure / 6.3

6.3 Heterostructures / 6.6

6.4 Double Heterostructure Laser / 6.7

6.5 Stripe Geometry Lasers / 6.10

6.6 Index-Guided Stripe Geometry Lasers / 6.12

6.7 Materials Growth / 6.13

6.8 Quantum Well Heterostructure Lasers / 6.14

6.9 Vertical Cavity Surface Emitting Lasers / 6.17 6.10 Laser Arrays / 6.18

6.11 Modulation of Laser Diodes / 6.21 6.12 Reliability / 6.23

6.13 References / 6.25

Chapter 7 Infrared Gas Lasers Michael Ivanco and Paul A Rochefort 7.1

7.1 Introduction / 7.1

7.2 Gas Laser Theory / 7.1

7.3 Specific Gas Lasers / 7.12

CONTENTS ix

Chapter 9 Ultrashort Optical Pulses: Sources and Techniques Li Yan,

9.1 Principles of Ultrashort Pulse Generation / 9.1

9.2 Methods of Generation / 9.5

9.3 Ultrashort Pulse Laser Systems / 9.18

9.4 Methods of Pulse Width Measurements / 9.26

9.5 Conclusions / 9.31

9.6 References / 9.32

10.1 Fundamental Physical Properties / 10.3

12.1 Theory of Fiber Transmission / 12.1

12.2 Materials for the Fabrication of Optical Fiber / 12.10

13.2 Linear Optics: The Harmonic Potential Well / 13.1

13.3 Nonlinear Optics: The Anharmonic Potential Well / 13.4

13.4 Second-Order Nonlinearities:␹ / 13.7

13.5 The Third-Order Susceptibilities:␹ / 13.9

13.6 Propagation Through Nonlinear Materials / 13.12

13.7 Acknowledgments / 13.27

13.8 References / 13.27

x CONTENTS

14.1 Phase Conjugation: What It Is / 14.1

14.2 Phase Conjugation: How to Generate It / 14.5

14.3 Applications / 14.30

14.4 References / 14.34

Chapter 15 Ultraviolet and X-Ray Detectors George R Carruthers 15.1

15.1 Overview of Ultraviolet and X-Ray Detection Principles / 15.1

15.2 Photographic Film / 15.1

15.3 Nonimaging Photoionization Detectors / 15.2

15.4 Imaging Proportional Counters / 15.7

16.7 Detection Systems and Selection Guide / 16.19

16.8 References and Further Reading / 16.21

17.6 Detection Systems and Selection Guide / 17.21

17.7 References and Further Reading / 17.23

18.1 Introduction / 18.1

18.2 Photosurfaces / 18.2

18.3 Imaging Tubes / 18.5

18.4 Solid-State Imaging Devices / 18.10

18.5 Imaging System Performance Model / 18.13

18.6 Modulation Transfer Functions / 18.19

18.7 Applications / 18.22

18.8 References / 18.23

CONTENTS xi

19.1 Introduction / 19.1

19.2 Theory of Holographic Imaging / 19.1

19.3 Volume Holograms—A Graphic Model / 19.6

19.4 Material Requirements / 19.9

19.5 General Procedures / 19.12

19.6 Current Applications / 19.13

19.7 References / 19.15

Chapter 20 Laser Spectroscopy and Photochemistry G Rodriguez,

20.1 Introduction / 20.1

20.2 Laser-Induced Fluorescence and Absorption Spectroscopy / 20.3

20.3 Photoionization and Photoelectron Spectroscopy / 20.12

21.2 Fiber-Optic Sensor Transduction / 21.1

21.3 Fiber-Optic Sensor Components / 21.9

Chapter 22 High-Resolution Lithography for Optoelectronics

23.5 Laser Hazard Classification / 23.7

23.6 Laser Hazard Assessment / 23.12

23.7 Laser System Safety / 23.13

23.8 The Safe Industrial Laser Laboratory / 23.14

23.9 Laser Eye Protection / 23.16 23.10 Laser Accidents / 23.23 23.11 Electrical Hazards / 23.24 23.12 Visitors and Observers / 23.24 23.13 Delayed Effects and Future Considerations / 23.24 23.14 Conclusions and General Guidelines / 23.25 23.15 References / 23.26

Chapter 24 Lasers in Medicine Ashley J Welch and M J C van Gemert 24.1

Chapter 25 Material Processing Applications of Lasers James T Luxon 25.1

25.1 Material Processing Lasers / 25.1

25.2 Laser Characteristics For Material Processing: Advantages and

Chapter 26 Optical Integrated Circuits Hiroshi Nishihara,

26.1 Features of Optical Integrated Circuits / 26.1

26.2 Waveguide Theory, Design, and Fabrication / 26.1

26.3 Grating Components For Optical Integrated Circuits / 26.9

26.4 Passive Waveguide Devices / 26.17

26.5 Functional Waveguide Devices / 26.24

26.6 Examples of Optical Integrated Circuits / 26.31

26.7 References / 26.35

CONTENTS xiii

Chapter 27 Optoelectronic Integrated Circuits Osamu Wada 27.1

27.1 Introduction / 27.1

27.2 Categories and Features / 27.1

27.3 Materials, Basic Devices and Integration Techniques / 27.3

27.4 Optoelectronic Integrated Circuits / 27.15

28.2 Optical Fiber Amplifiers / 28.1

28.3 Semiconductor Optical Amplifiers / 28.7

28.4 Planar Waveguide Amplifiers / 28.8

28.5 Performance Parameters / 28.8

28.6 Applications / 28.14

28.7 Conclusions / 28.15

28.8 References / 28.15

Chapter 29 High-Speed Semiconductor Lasers and Photodetectors

PREFACE TO SECOND EDITION

It’s often difficult to predict which areas of a field will become rejuvenated and grow rapidly

or spin off to fit with another to form something new The field of electro-optics is alsounpredictable, but currently it has numerous forces acting on it First is the development ofnew optical sources such as ultrafast lasers and fiber lasers to compete with semiconductordevices for pumping and lasing The vast riches that can be obtained by work outside thevisible seem to be opening up Sources and fibers for telecommunications are moving aheadrapidly and new display devices may eventually bring an end to the vacuum tube cathoderay tubes We believe that the material in this book will find an interested audience for manyyears

This second edition of the Electro-Optics Handbook both updates individual chapters

where needed and adds additional chapters where new fields have emerged Electro-opticsremains a dynamic area and that will continue and broaden into many new areas Our thanks

to Steve Chapman for his help getting this edition in progress and to Marcia Patchan andPetra Captein for much of the work to move it toward composition

Ronald W Waynant Marwood N Ediger

PREFACE TO FIRST EDITION

Our concept for a new handbook on electro-optics integrates sources, materials, detectorsand ongoing applications The field of electro-optics now encompasses both incoherent op-tical sources and lasers that operate from the millimeter wavelength region to the x-rayregion In this handbook we provide coverage of the most important laser sources in thiswavelength range Having chosen a broad range of wavelengths from our sources, we thendefine the properties of the materials through which these sources might travel From there

we consider the detectors that might be used to observe them When all the componentshave been covered, we consider the applications for which electro-optical systems can beused

The applications for electro-optics systems is growing at a phenomenal rate and will mostlikely do so for the next fifty years or more Applications range from the astronomical tothe microscopic Laser systems can track the moon and detect small quantities of atmosphericpollution Laser beams can trap and suspend tiny bacteria and help measure their mechanicalproperties They can be used to clip sections of DNA The applications that we have included

in this handbook are only the beginning of applications for this field

This handbook is intended as a reference book It can be used as a starting place to learnmore about sources, materials, detectors and their use and applications Most chapters have

a considerable list of references to original research articles, or else refer to books that containsuch lists of references Liberal use is made of tables of data and illustrations that clarifythe text The authors are all experts in their fields

We make no statement that this handbook is complete although it was our goal to worktoward complete coverage of this field It is a dynamic field continually advancing andchanging We hope to follow these changes and to strive for further completeness in futureeditions We believe electro-optics will be part of a new field with new ways of transferringknowledge We hope to use these new fields to find additional ways to present data andknowledge that will be even more comprehensive

We are indebted to Daniel Gonneau of McGraw-Hill for suggesting this project and thenproviding the encouragement and motivation to see it through As editors we are grateful tothe authors who made great sacrifices to complete their contributions and who made our jobquite pleasant We hope that references are made to the authors and their sections because

it is with these authors that the knowledge presented here really resides We would be remissnot to mention Paul Sobel for his help and encouragement during the finishing stages of thisbook and to thank Eve Protic for her help during the many stages of production

Ronald W Waynant Marwood N Ediger

ACRONYMS

periodic table

Gyroscope

Vestigal Side Band

Institute

etching

spectroscopy

Radiological Health (of FDA)

FAFAD fast axial flow with axial

discharge

Administration

FET-SEED field-effect transistors

self-electro-optic effect devices

transverse discharge

GRIN-SCH graded index waveguide

separate confinementheterostructure

epitaxy

compensation

Commission

ACRONYMS xxiii

tellurium phosphate

anastomosis

LiTaO3 lithium tantalate

LLLTV low light level television

Laboratory

photodiode

and Technology

resonance

multiphoton ionization

spectroscopy

spectroscopy

mode-locking

dischargeSAM-APD separate absorption and

multiplication layers

heterostructure

bombardment-inducedresponse

SEED self-electro-optic effect

amplifiers

SNRD signal to noise ratio of a

displaySNRDT signal to noise ratio of a

display at thresholdSNRVO signal to noise ratio of video

(for white noise)

amplifiers

ACRONYMS xxv

TVL / PH television lines / picture height

emitting lasers

multiplexer

multiplexing

amplifiers

fluoride

The second edition of this handbook attempts to cover a broad spectral bandwidth—fromx-rays to far infrared A primary motivation in extending the short-wavelength limit of thesource spectrum, and the handbook’s coverage of it, is the demand for higher resolvingpowers in materials and device fabrication applications as well as medical and biologicalimaging Figure 1.1 depicts the size of objects of interest in the biological, materials science,and electronics worlds, and the wavelength necessary to resolve them as prescribed by theRayleigh criterion The infrared boundaries of the spectrum are also continually beingstrained by sources, materials, and detectors in the development of a variety of applicationssuch as imaging, optical diagnostics, and spectroscopy.

Each chapter of this handbook falls into one of four categories: sources, materials, andtheir properties (e.g., nonlinear optics), detectors, and applications In the remainder of thischapter we present some simple overlying principles of each category and a topical map toaid the reader in finding the desired information

1.2 TYPES OF LIGHT SOURCES

Chapter 2 takes a detailed look at incoherent sources, and Chaps 3 through 8 are devoted

to the numerous laser sources grouped in part by media and in part by wavelength Ultrashort

1.2 CHAPTER ONE

FIGURE 1.1 Relation of object size and resolving wavelength.

pulse lasers and techniques are covered in Chap 9 Chapter 28 picks up the new field offiber lasers and amplifiers—an important new direction

Although the activity in the field of electro-optics has often been mirrored by events inlaser development, incoherent sources still have an important role Lasers are much newerand more space is devoted to them in the chapters to follow; however, the inescapable fact

is that lamps currently have a much greater effect on our everyday lives than do lasers Withhundreds of millions of plasma discharge lamps and billions of incandescent light bulbs inconstant use on a worldwide basis, power expenditure on lighting alone approaches theTerawatt level Even the 22 percent or lower efficiency of most lamps still exceeds that ofmost lasers

Arc lamps are characterized by high currents (several amperes) and high pressures mospheres) with ballast resistors used to prevent complete runaway The lamps can be ex-ceedingly bright Examples include high-pressure (3 to 10 atmosphere) mercury vapor arclamps, high-pressure metal halide lamps, high-pressure xenon arc lamps, high-pressure so-dium arc lamps, as well as xenon flash lamps and rf excited lamps They are used wherehigh brightness is required for such purposes as movie projection, solar simulation, large-area illumination, and other special-purpose illumination

(at-Lower-pressure discharges (a few Torr) are used to excite atomic gases such as mercuryvapor, hydrogen, cesium, the rare gases, and other elements The best-known example of

INTRODUCTION TO ELECTRO-OPTICS 1.3

FIGURE 1.2 Location of generic lasers on the wavelength scale.

these low-pressure lamps is the fluorescent lamp The low-pressure discharge gives rise toemissions characteristic of the gas in the tube Mercury is especially valuable, since a mer-cury discharge gives about 90 percent of its emission in the mid-ultraviolet at 253.7 nm.This mid-ultraviolet emission is capable of exciting a thin phosphor coating on the inside ofthe glass tube The phosphor subsequently fluoresces rather uniformly over the visible spec-trum, thereby giving off ‘‘white’’ light The entire process is quite efficient compared withincandescent bulbs An essentially similar energy transfer process produces compact fluo-rescent tubes, germicidal ultraviolet lamps, low-pressure sodium lamps, neon signs, glowlamps, and hollow-cathode lamps

There is still work to do to understand and improve lamps Because of the great usagefor fundamental necessities of life, improvements such as greater efficiency, lower emission

of ultraviolet (uv) and infrared (ir), and longer life can be of great benefit The currentunderstanding of nonequilibrium plasmas, near local thermal equilibrium (LTE), and LTEplasmas can be found in several references.1,2An improved understanding of the mechanisms

of these plasmas is the key to producing better light sources

Lasers are of such importance to modern electro-optics that six chapters have been voted to them They are categorized both according to the spectral region in which they emitand according to the type of material used to obtain lasing This categorization seems to suitthe majority of lasers rather well In Chap 3 x-ray, vacuum-ultraviolet (vuv), and uv lasersare covered Most of the lasers in this spectral region are gaseous (atom, ion, or plasma),but occasionally a solid medium is available and more are expected in the future Chapter

de-4 considers visible lasers including dye lasers, except solid-state lasers, which have becomeimportant enough to warrant both Chap 5 on conventional solid-state lasers and Chap 6 onsolid state semiconductor lasers The lasers in these two chapters fall over parts of the visibleand infrared The remainder of the infrared belongs largely to gas lasers and is covered inChap 7 Figure 1.2 gives an overview of where the various generic types of lasers fall onthe wavelength scale Specific lasers, most of which have been commercialized or otherwisehave noteworthy characteristics, are denoted in detail in Fig 1.3 Further information onspecific lasers can be found in several places in the open literature.3,4

Chapter 8 covers free electron lasers (FELs) which operate by magnetically perturbing

an accelerated electron beam and which have vast tunability To date these lasers have erated primarily in the infrared, but they are anticipated to operate tunably in the visible inthe near future and eventually may provide ultraviolet and x-ray beams

op-1.4 CHAPTER ONE

FIGURE 1.3 Detailed location of specific lasers.

Many lasers have yielded to a variety of techniques that produced incredibly shortpulsewidths—some only a few femtoseconds wide—and these lasers will be used in a widevariety of electro-optics, physics, chemistry, and biology experiments which will yield newinformation, new insight, and further progress and products The techniques for producingultrashort pulses are given in Chap 9 Applications of these lasers will grow rapidly as soon

as the production of the ultrashort lasers themselves becomes solidly commercialized ter 29—new—points to high-speed semiconductor lasers and photodetectors which maybranch into better communications devices and span other new applications

Chap-It is interesting to reflect on the reasons that so many lasers occur in the visible and nearinfrared It is primarily a matter of materials, pumping sources, and the basic physics oflasers themselves Because the human eye responds to radiation in the 400 to 700-nm region,considerable development of materials which transmit in the visible has taken place Infraredinstruments, especially military instruments, have also encouraged development of infraredmaterials Most optical sources, lamps, arcs, and flashlamps (and now diode lasers) emitmost easily in the infrared as well In addition, the small signal gain of a laser is directlyproportional to the square of the wavelength Related factors increase the dependence ofgain on wavelength to the third or fourth power For all these reasons, it is much harder tomake uv, vuv, or x-ray lasers than it is to make infrared lasers

1.3 MATERIALS

Materials that are nonabsorbing over a broad bandwidth are critical to source (and detector)development We first consider the linear optical properties of materials—the responses thatare proportional to the incident electric field Optical materials are covered in two chapters

INTRODUCTION TO ELECTRO-OPTICS 1.5

FIGURE 1.4 Transmission windows of some common optical materials.

that are roughly divided by wavelength Material properties in the ultraviolet and shorterwavelengths are dealt with in Chap 10, while Chap 11 contains information about visibleand infrared optical materials The special material properties and techniques of optical fibersare covered in Chap 12 Perhaps the most crucial linear optical specification of a material

is its transmission bandwidth, since this determines its suitability for use as a window, filtersubstrate, or fiber Figure 1.4 gives a quick survey of the transmission bandwidth of somecommon optical materials

Optical fields can also induce polarizations in materials that depend upon second- andhigher-order powers of the field intensity These nonlinear material responses lead to a variety

of elastic and inelastic interactions between the media and the optical field Nonlinear actions of both categories including harmonic generation, four-wave mixing, and stimulatedscattering are described in Chap 13 while phase conjugation is treated in Chap 14

in the visible and infrared region Figure 1.5 surveys the spectral coverage of numerous

1.6 CHAPTER ONE

FIGURE 1.5 Spectral response windows of numerous detector types.

detector types, subgrouped by operational mode including photoemissive, quantum, and mal devices Some data, e.g for thermophiles, could work over the entire range of wave-lengths, but are given here for the most common region Finally, imaging detectors aredescribed in Chap 18

ther-1.5 CURRENT APPLICATIONS

Two-thirds of our space has been devoted to the principles of generation of light, transmission

of light through optical materials, and detection of light The remainder of the handbook isdevoted to specific applications which extend the techniques and devices to broad areascapable of generating new knowledge

Holography is the subject of Chap 19 Holography has a tremendous number of cations, primarily in the area of nondestructive testing Holographic interferometric anddouble-exposure techniques can determine small movements in surfaces and thereby detectfaults in materials or structures These techniques are extremely valuable, but holographyalso has value in creating unique art forms This chapter sets forth basic principles whilealso giving new techniques for practical implementation of holography

appli-Laser spectroscopy is presented in Chap 20 This topic has many direct and ongoing uses

in basic research in physics, chemistry, and biology and in applications such as remotesensing, combustion diagnostics, and medical diagnostics and imaging

Fiber-optic sensors, covered in Chap 21, is an emerging field that shows great potential.The ability to position these sensors discretely in perhaps hazardous or inaccessible locations

is but a part of their allure Already fiber sensors are used in numerous applications includingsurveillance, temperature, pressure, and displacement measurements, and a variety of medicalprobes

INTRODUCTION TO ELECTRO-OPTICS 1.7

The principles of lithography for optoelectronics are presented in Chap 22 Lithographyinvolves many of the topics covered in this handbook including vuv and x-ray sources andoptics, holography, material properties, and laser chemistry of resists

The important subject of laser safety is covered in Chap 23 While laser safety in theresearch lab will continue to be an essential concern, as more lasers continue to appear inindustrial and consumer settings laser safety issues will become even more diverse and acute.Chapter 24 presents a broad view of lasers in medicine Medical applications both inpractice and in development include a range of uses such as diagnostics, surgery, laser-induced activation of pharmaceuticals (photodynamic therapy), and imaging This chapterdiscusses the current usage of lasers in medicine and surgery, the underlying physics pertinent

to those applications, and an array of information regarding tissue optics

Applications of lasers in material processing are described in Chap 25 Processes such

as hardening, alloying, and cladding where the laser has unique attributes are presented Theadvantages and disadvantages of the use of lasers in lieu of traditional tools for welding,cutting, drilling, and marking are detailed Also, the use of lasers for microelectronic appli-cations is surveyed

The principles of optical integrated circuits and optoelectronic integrated circuits are ered in Chaps 26 and 27 Combining an array of electro-optic devices in miniature forminvolves integrating diode lasers, detectors, materials, and fiber optics The topics and devicesdescribed in these last two chapters are undoubtedly critical to the future of computing,communication, and a continuing development of smaller but smarter devices that will furtherimprove our quality of life

cov-Finally, the two new chapters have been added to cover the newly emerged fields ofoptical amplifiers (Chap 28) and fast lasers and detectors (Chap 29) We believe thesedevices will have a large impact

3 R Beck, W Englisch, and K Ours, Table of Laser Lines in Gases and Vapors, Springer-Verlag, 2nd

ed New York, 1978.

4 R Waynant and M Ediger, Selected Papers on UV, VUV and X-Ray Lasers, vol MS71, SPIE

Mile-stone Book Series, 1993.

dis-In addition, the practical aspects of proper measurements and the problems associated withthis task are discussed.

2.2 DEFINITION OF TERMS

The wavelength region for optical radiation spans from approximately 100 nanometers (nm)

to 1000 micrometers (␮m) The optical radiation spectrum can be broken up into three basicregions:

to 14␮m), and ‘‘far’’ (14 to 1000␮m) categories in the ir In photobiology or photomedicine,

it is more common to use biologically meaningful divisions, or the A,B, and C categories

as defined by the CIE.1They are: UVC (100 to 280 nm), UVB (280 to 315 nm), and UVA(315 to 400 nm) for the uv region, and IRA (760 to 1400 nm), IRB (1400 to 3000 nm), andIRC (3␮m to 1 mm) for the ir region

In order to discuss the characteristics of noncoherent optical radiation, it is first necessary

to define certain terms and quantities Tables 2.1 and 2.2 list several of the commonly used

2.2 CHAPTER TWO

TABLE 2.1 Radiometric Units

Radiant exposure (dose)†

† Common terminology in photobiology.

TABLE 2.2 Photometric Units

* These units still appear in some texts, although the SI units are now the preferred system.

SI units2of optical radiation for radiometry and photometry Although most of the quantities

in Tables 2.1 and 2.2 are listed in terms of the square meter (m2), the preferred unit of areafor optical radiation is cm2because this more closely approximates the sensitive area of mostdetectors The nm is the preferred unit of wavelength in the ultraviolet to mid-infrared portion

of the electromagnetic spectrum Thus, when discussing ‘‘spectral’’ quantities, i.e., ‘‘per unitwavelength,’’ all terms in Tables 2.1 and 2.2 would be modified by the suffix ‘‘per nm’’ andsubscript ␭ The spectral quantity may then be integrated over the wavelength region ofinterest to obtain total flux, intensity, etc., in a specified wavelength band If one is talking

NONCOHERENT SOURCES 2.3

FIGURE 2.1 Pictorial demonstration of ‘‘solid angle’’

in a spherical coordinate system The solid angle is fined by the area intercepted by the irregular cone on a

de-sphere of radius r.

about wavelengths in the infrared region greater than 1000 nm, the convention is to use␮m

or microns, instead of nm

2.2.1 Solid Angle

Shown in Fig 2.1, the solid angle⍀is defined as the area of some ‘‘irradiated’’ surface da s,

divided by the distance from the source r squared.

da s

r This distance r equals the radius of a sphere which is centered at the vertex of the solid angle Thus the area da sis the area of the intercepted spherical surface In spherical coor-dinates,

2.4 CHAPTER TWO

FIGURE 2.2 Schematic diagram of a simple radiometer demonstrating invariance of radiance.

As long as the optical radiation from the source overfills the input aperture of area A1 , the power

per unit area at the detector surface A2 will not change.

D

r

2.2.2 Radiant Intensity and Radiance

In the previous section, the concept of solid angle was introduced This quantity is an

im-portant geometrical concept for the discussion of radiant intensity I and radiance L The

formal definition of intensity in the field of radiometry is different from the definition in thefield of physical optics (W / m2) In the field of radiometry, radiant intensity is defined as theflux of radiation in a given angular direction (W / sr) The radiant intensity in any solid angle

is the flux, or power, emitted within that angle divided by the size of that solid angle, in sr

The radiance can be thought of as the radiant intensity of a source divided by the projected

image area of this source, where the projected area lies in the plane normal to the direction

of propagation

The significant characteristic of radiance is its property of invariance through a lossless

optical system It can be shown3that, within an isotropic medium, the value of L in the

direction of any ray has the same value at all points along that ray, neglecting losses by

absorption, scattering, or reflections This is known as the radiance theorem.4Knowledge ofthe radiance of a source enables one to determine the radiant power flowing through anysurface if the cross-sectional area of the surface and its solid angle are known This isespecially useful in complex optical systems that may contain multiple aperture and fieldstops An aperture stop is defined as any element, be it the edge of a lens or an opendiaphragm, that forms a boundary which limits the amount of light that passes through theoptical system The amount of light is limited by the reduction in the number of rays (from

an object) reaching the final image plane The field stop governs the size of the final imageand thus determines the FOV (field of view) of the optical system

The invariance of radiance can be easily visualized with the aid of Fig 2.2 This

config-uration could be used as a simple radiometer with a detector of sensitive surface area A2and

input aperture of area A1 Assuming X is significantly larger than the diameter of the detector,

the detector will subtend the same solid angle at all points of the input aperture If we place

an ‘‘extended’’ (i.e., of finite dimension) source in front of this instrument, such that theradiation field overfills the input aperture, then

NONCOHERENT SOURCES 2.5

LA A1 2

X where P⫽total radiant power incident on the detector (This neglects losses due to absorp-tion, reflection, or scattering.) This equation will hold regardless of the distance between thesource and the input aperture, as long as the beam overfills the input aperture If the distancefrom the source is increased further, the beam no longer overfills the input aperture Thisresults in a reduction of the crosssectional area on the detector and, therefore, a reduction

in the power measured by the detector The quantity A⍀is solely dependent upon the ometry of the optical system and is known as the throughput, or the ‘‘entendue’’ of thesystem

ge-2.2.3 Photometric Units vs Radiometric Units

Radiometric quantities are applicable across the entire electromagnetic spectrum There isanother analogous system of units that is applicable only in the visible portion of the spec-trum (from 380 to 780 nm) as defined by the CIE These are used in the field of photometry(the measurement of visible light) and are listed in Table 2.2 In radiometry, the primary unit

of radiation transfer, or radiant flux, is the watt (W) In photometry, the corresponding unit

is the lumen (lm), which signifies the visual response produced by a light source with a

given output power (W)

There is no direct method of converting from luminous flux (lumens) to radiant flux,unless the exact spectral distribution is known and is limited to the visible portion of thespectrum Ordinarily, one would apply the following equations:

K (␭) is defined as the spectral luminous efficacy, which is the ratio of any photometric unit

to its radiometric equivalent and has units of lumens per watt If normalized to its peak value

Kmax, it is referred to as spectral luminous efficiency V (␭) The term ‘‘efficiency’’ as usedhere refers to the relative ability of the light to stimulate the visual response in the eye.Thus,

K (␭)

Kmax

V (␭) is defined as the photopic (daylight-adapted sensitivity of the human eye) spectral

luminous efficiency and V⬘(␭) is the scotopic (night-adapted) spectral luminous efficiency

Plots of both V (␭) and V⬘(␭) are shown in Fig 2.3

For photopic weighting,

Kmax⫽673 lm / Wand for scotopic,

Kmax⫽1725 lm / WTherefore, Eqs (2.6) and (2.7) and the appropriate above constants can be applied to cal-culate the equivalent photometric quantities from their radiometric counterparts

† The subscriptsv and e are used to differentiate between photometric and radiometric quantities.

2.6 CHAPTER TWO

FIGURE 2.3 Spectral plot of the photopic V (␭) and scotopic V⬘ ( ␭ ) functions The photopic function defines the spectral daylight-adapted sensitivity of the eye, while the scotopic function defines the spectral night-adapted sensitivity of the eye.

The current standard unit in photometry is defined as the candela, the luminous intensity

of monochromatic radiation at 555 nm whose radiant flux is equal to 1 / 683 W The humaneye is most sensitive at this wavelength Between 1948 and 1979, the unit of luminousintensity was defined as one-sixtieth of the luminous intensity of 1 cm2from a blackbody atthe freezing point of platinum This is consistent with the current definition, which lies withinthe error limits that resulted from the uncertainty in the freezing point of platinum.5Previous

to 1948, the standard was based on the output of a group of carbon-filament vacuum lamps.The predictability of this standard was limited by the fact that the lamp intensities werehighly dependent on their physical construction or manufacture

2.3 CHARACTERISTICS

2.3.1 Point Sources

A frequently encountered concept in radiometry is that of a point source A point sourceradiates uniformly in all directions (i.e., it is isotropic); the waves emanating from it can beconsidered to be spatially coherent, and its radiative transfer obeys the inverse square law.The inverse square law simply states that either the irradiance or the intensity of a sourcefalls off in a manner proportional to the square of the distance from the source Althoughthe ideal point source does not exist, it is acceptable to talk about sources whose dimensionsare very small in relation to their distance of observation A star is a good example, itsdistance being so great that it subtends an extremely small angle as seen from the earth In

general, if the maximum source dimension D is less than one-tenth of the distance r from

the source, then assuming inverse square law behavior will result in an error of less than 1

NONCOHERENT SOURCES 2.7

percent If D is less than one-twentieth of the distance r, the error will be less than 0.1

percent However, if one is dealing with a highly collimated light source, the distance essary to achieve inverse square law behavior will be much greater, owing to the effects ofthe collimating optics.6

nec-2.3.2 Lambertian Sources

Lambertain sources are defined as sources which have a constant radiance L for all viewing

angles A blackbody is, by definition, Lambertian A good approximation to a Lambertiansurface is a white piece of paper The radiance, or apparent brightness, does not change as

a function of viewing angle An example of an extremely non-Lambertian source would be

a bank of fluorescent lamps When viewed normal to their surface, the dark areas betweenthe bulbs would be clearly visible However, if one were to view them at grazing incidence,they would appear to be a solid sheet of light Therefore, the brightness, or radiance, would

be different depending on the viewing angle If we look at the relationships between radiance,intensity, and solid angle from Table 2.1:

d⌽ I cos␪

FIGURE 2.4 Spherical coordinate system

demon-strating projected area, where da⫽dA cos␪

This equation demonstrates Lambert’s cosinelaw, which states that the irradiance de-creases as the observation angle increases.Integrating both sides of Eq (2.8) and sub-

stituting for d␾, we obtain

I⫽冕L cos␪d A (2.13)Since the radiance of a Lambertian source isindependent of angle ␪, Eq (2.13) can beeasily integrated to yield

I⫽LA cos␪ (2.14)

2.8 CHAPTER TWO

FIGURE 2.5 Spherical coordinate system as an aid to

the calculation of the exitance M of a source of area dA1

at a distance of R from the source.

The product LA will be a fixed quantity; therefore, I is solely dependent on the viewing

angle of the source This decrease in intensity as the viewing angle increases from 0⬚ (orfrom the normal to the surface) is entirely due to the decreased projected area of the source

2.3.3 Extended Sources

The term ‘‘extended source’’ is commonly used to describe most real sources, i.e., sources

of a finite size (as opposed to the ideal point source) that are not necessarily Lambertian.When evaluating the irradiance, or illuminance, from general extended sources, it is often

useful to speak of the radiant or luminous exitance M of the source In lighting engineering,

the exitance is the starting point for determining the illuminance of numerous differentgeometrical configurations In fact, illumination engineers use tables of ‘‘configuration fac-tors’’ to calculate light levels based on the geometry of their task Referring to Fig 2.5, the

exitance M can be calculated from a knowledge of the radiance L of the source by the

following series of equations:

Once the exitance M is known, the illuminance or irradiance can be determined for any

source configuration The general expression is

where E2⫽ the illuminance or irradiance at a point P2, M1is the exitance of A1, and C2⫺1

is the configuration factor from surface 1 to point 2 The configuration factor is determined

by an area integral which describes the relationship between the area of the source and the

point P2 Assume we want to determine the irradiance at the point P2of the disk Lambertiansource in Fig 2.6 The formal derivation can be found in Boyd.7The final solution is

This case obeys the inverse square law since the irradiance is dependent on the fixed quantity

␲Lr2and falls off as a function of the square of the distance from the source

E⫽ ␲L

4 rⰇD

This results because r2⫹ D2⬃ r2as long as D is sufficiently smaller than r as to be

insignificant This demonstrates that the irradiance remains almost constant for a large, planarsheet of light until one is at least half a radius away from it An excellent reference forconfiguration factors is the ‘‘Catalog of Selected Configuration Factors.’’8

2.4 MEASUREMENTS AND CALIBRATION

Accurate measurements of noncoherent optical radiation are very difficult and can only beaccomplished by accounting for all the potential sources of error For instance, reflectors andapertures will affect the spatial distribution and therefore the intensity variation with distance.Most sources do not produce uniform illumination over an irradiated surface, and this must

be considered when choosing the location of the detector It is important to know the sourcecharacteristics and geometry before attempting to perform high-accuracy measurements

2.4.1 Instrumentation

The power (or flux) from a noncoherent light source can be measured with a variety ofinstruments, depending on the application or the desired degree of precision To determinetotal light output, one could use a photometer or radiometer Photometers measure visiblelight in lumens, while radiometers are capable of measuring the entire spectrum of opticalradiation, in watts These instruments measure total light incident upon a detector (either asolid-state or photomultiplier tube) and are therefore highly dependent on the spectral sen-sitivity of the particular detector Filters placed in front of the detector can significantly alterthe instrument’s spectral response, as is demonstrated by Fig 2.7

A photometer’s detector is filtered so that its response closely matches that of the humaneye A typical portable photometer uses a photovoltaic or photoconductive cell, connected

to a meter which is calibrated directly in lux (lumens / m2), or footcandles Photovoltaicdetectors operate by generating a voltage as the result of the absorption of a photon Thesetypes of detectors have poor linearity of response at high levels of incident illumination,which must be compensated for by external circuitry Photoconductive detectors are con-structed of materials whose resistance changes with photon absorption (For a detailed dis-cussion of solid-state detector characteristics, see Chaps 15–18.)

For laboratory, or low-light-level applications, a photomultiplier tube (PMT) is more likely

to be used The photomultiplier tube is a photoemissive detector as opposed to a photovoltaic

or photoconductive detector The PMT operates via the photoelectric effect These detectorsproduce current when light is absorbed by a photoemissive surface which is then amplified

in sequential stages Photomultipliers (PMTs) are extremely sensitive and are capable ofrapid response times but require a high voltage (500 to 5000 V) for operation The disad-

NONCOHERENT SOURCES 2.11

FIGURE 2.7 The spectral response of a bare silicon detector, and of a

silicon detector modified by a radiometric filter (Adapted from Ref 14

with permission.)

vantages of these detectors are their fragility—they are extremely sensitive to mechanicalshock, interference from electromagnetic fields, moisture, and temperature Some are rec-ommended for use at temperatures down to 45⬚C below ambient (⬇⫺20⬚C) Thus, in addition

to the high-voltage supply, the PMT may require an external cooling device For thesereasons, a PMT-based instrument is not well suited to field use PMTs also tend to producehigh dark currents (signal when no light is incident on the tube) which must be subtractedfrom the intended signal Figure 2.8 shows the spectral response characteristics of severalcommercially available PMTs

The spectral sensitivity of a radiometer will depend on what type of semiconductor (fornon-PMT instruments) and filters are used in the detector Currently, most of these types ofdetectors are classified generically as ‘‘photodiodes’’ which produce current in proportion tothe incident illuminance Ideally, a radiometer will have a detector that is ‘‘spectrally flat’’over the wavelength region of interest Silicon detectors (most sensitive in the visible andnear-ir region) can be doped to increase the sensitivity in the ultraviolet region Anothertechnique which is sometimes employed in broadband uv meters is to place fluorescentphosphors in front of the photodetector The uv radiation impinges on the phosphor surfaceand is then transformed into visible radiation to which the semiconductor is more sensitive.The most pervasive obstacle in making accurate measurements of uv radiation with unso-phisticated instrumentation is the fact that most sources which emit uv also emit visible, andeven ir, radiation in much greater intensities A uv-transmitting, but visible-blocking filter isnormally inserted above the phosphor to limit the transmission of the undesired visiblewavelengths from the source to the detector The spectral transmittance of a commerciallyavailable filter which exhibits this type of behavior is shown in Fig 2.9 Unfortunately, thesefilters’ transmittance usually starts to increase again in the near-ir When it is desired tomeasure the ir radiation from a source, detectors made of materials other than silicon [e.g.,germanium (Ge) and lead sulfide (PbS)1 are often chosen The spectral sensitivity of severalcommercially available detectors is shown in Fig 2.10

2.12 CHAPTER TWO

FIGURE 2.8 The spectral response characteristics of several commercially available

photo-multiplier tubes (PMTs) (Modified with permission from Hamamatsu Corp Jan / 89 (Rev),

T-7000, p 77.)

FIGURE 2.9 The spectral transmittance of a commercially available (Hoya Optics U-330) uv-passing, visible blocking glass filter.