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Abstract

This section contains the introduction to the series, the preface, the table of contents, and the glossary of symbols.

Library of Congress Cataloging-in-Publication Data

Daniels, Arnold.

Field guide to infrared systems, detectors, and FPAs / Arnold

Daniels. − 2nd ed.

p. cm. − (The field guide series)

Rev. ed of: Field guide to infrared systems / Arnold Daniels.

© 2007.

Includes bibliographical references and index.

ISBN 978-0-8194-8080-4 (alk. paper)

1. Infrared technology–Handbooks, manuals, etc. 2. Optical detectors—Handbooks, manuals, etc. 3. Focal planes–Handbooks, manuals, etc. I. Title.

TA1570.D36 2010

621.362–dc22

2010000421

Published by

SPIE

P.O. Box 10

Bellingham, Washington 98227-0010 USA

Phone: +1.360.676.3290

Fax: +1.360.647.1445

Email: books@spie.org

Web: http://spie.org

The content of this book reflects the work and thought of the author. Every effort has been made to publish reliable and accurate information herein, but the publisher is not responsible for the validity of the information or for any outcomes resulting from reliance thereon.

Printed in the United States of America.

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Introduction to the Series

Welcome to the SPIE Field Guides—a series of publications written directly for the practicing engineer or scientist. Many textbooks and professional reference books cover optical principles and techniques in depth. The aim of the SPIE Field Guides is to distill this information, providing readers with a handy desk or briefcase reference that provides basic, essential information about optical principles, techniques, or phenomena, including definitions and descriptions, key equations, illustrations, application examples, design considerations, and additional resources. A significant effort will be made to provide a consistent notation and style between volumes in the series.

Each SPIE Field Guide addresses a major field of optical science and technology. The concept of these Field Guides is a format-intensive presentation based on figures and equations supplemented by concise explanations. In most cases, this modular approach places a single topic on a page, and provides full coverage of that topic on that page. Highlights, insights, and rules of thumb are displayed in sidebars to the main text. The appendices at the end of each Field Guide provide additional information such as related material outside the main scope of the volume, key mathematical relationships, and alternative methods. While complete in their coverage, the concise presentation may not be appropriate for those new to the field.

The SPIE Field Guides are intended to be living documents. The modular page-based presentation format allows them to be updated and expanded. We are interested in your suggestions for new Field Guide topics as well as what material should be added to an individual volume to make these Field Guides more useful to you. Please contact us at fieldguides@SPIE.org.

John E. Greivenkamp, Series Editor

College of Optical Sciences

The University of Arizona

The Field Guide Series

Field Guide to Geometrical Optics, John E. Greivenkamp (FG01)

Field Guide to Atmospheric Optics, Larry C. Andrews (FG02)

Field Guide to Adaptive Optics, Robert K. Tyson & Benjamin W. Frazier (FG03)

Field Guide to Visual and Ophthalmic Optics, Jim Schwiegerling (FG04)

Field Guide to Polarization, Edward Collett (FG05)

Field Guide to Optical Lithography, Chris A. Mack (FG06)

Field Guide to Optical Thin Films, Ronald R. Willey (FG07)

Field Guide to Spectroscopy, David W. Ball (FG08)

Field Guide to Infrared Systems, Arnold Daniels (FG09)

Field Guide to Interferometric Optical Testing, Eric P. Goodwin & James C. Wyant (FG10)

Field Guide to Illumination, Angelo V. Arecchi; Tahar Messadi; R.John Koshel (FG11)

Field Guide to Lasers, Rüdiger Paschotta (FG12)

Field Guide to Microscopy, Tomasz S. Tkaczyk (FG13)

Field Guide to Laser Pulse Generation, Rüdiger Paschotta (FG14)

Field Guide to Infrared Systems, Detectors, and FPAs, Second Edition, Arnold Daniels (FG15)

Field Guide to Laser Fiber Technology, Rüdiger Paschotta (FG16)

Field Guide to Infrared Systems, Detectors, and FPAs, 2nd Edition

Field Guide to Infrared Systems, Detectors, and FPAs, Second Edition, is written to clarify and summarize the theoretical and practical principles of modern infrared technology. It is intended as a reference for the practicing engineer and/or scientist who requires effective practical information to design, build, and/or test infrared equipment in a wide variety of applications.

This book combines numerous engineering disciplines necessary for the development of an infrared system. It describes the basic elements involving image formation and image quality, radiometry and flux transfer, and explains the figures of merit for detector performance. It considers the development of search infrared systems and specifies the main descriptors used to characterize thermal imaging systems. Furthermore, this guide clarifies, identifies, and evaluates the engineering tradeoffs in the design of an infrared system.

The 2nd edition provides the reader with an up-to-date view of the various third-generation infrared focal plane array (IRFPA) technologies currently in use or being actively researched. It also includes an overview of a new target acquisition model known as the “Targeting Task Performance (TTP) metric.” The applicability of this range performance model extends to sample imagers, digital image enhancement, and other features of modern imaging systems.

I would like to acknowledge and express my gratitude to my professor and mentor Dr. Glenn Boreman for his guidance, experience, and friendship. The knowledge that he passed on to me during my graduate studies at CREOL ultimately contributed to the creation of this book. I also would like to thank Dr. Boreman for reviewing a draft copy of the IRFPA 2nd edition manuscript.

I extend my sincere appreciation to Dr. Mel Friedman, NVESD, who took upon himself the onerous task of improving and clarifying the TTP metric concepts and its contents.

Above all, I voice a special note of gratitude to my kids Becky and Alex and my wife Rosa for their love and support.

Lastly, I would particularly like to thank you, the reader, for selecting this book and taking the time to explore the topics related to this motivating and exciting field. I trust that the contents of this book will prove interesting and useful to engineers and scientists working in one of the various infrared fields.

This Field Guide is dedicated to the memory of my father and brothers.

Arnold Daniels

October 2010

Table of Contents

Glossary of Symbols xi

Introduction 1

Electromagnetic Spectrum 1

Infrared Concepts 2

Optics 3

Imaging Concepts 3

Magnification Factors 4

Thick Lenses 5

Stops and Pupils 6

F-number and Numerical Aperture 7

Field of View 8

Combination of Lenses 9

Afocal Systems and Refractive Telescopes 10

Cold-Stop Efficiency and Field Stop 11

Image Quality 12

Image Anomalies in Infrared Systems 14

Infrared Materials 15

Ceramic and Amorphous Materials 19

GASIR Chalcogenide Glass Materials 20

Material Dispersion 21

Atmospheric Transmittance 23

Radiometry and Sources 24

Solid Angle 24

Radiometry 25

Radiometric Terms 26

Flux Transfer 28

Flux Transfer for Image-Forming Systems 29

Source Configurations 30

Blackbody Radiators 32

Planck’s Radiation Law 33

Stefan-Boltzmann and Wien’s Displacement Laws 35

Rayleigh-Jeans and Wien’s Radiation Laws 36

Exitance Contrast 37

Emissivity 38

Kirchhoff’s Law 39

Emissivity of Various Common Materials 40

Radiometric Measure of Temperature 41

Collimators 43

Performance Parameters for Optical Detectors 44

Infrared Detectors 44

Primary Sources of Detector Noise 45

Noise Power Spectral Density 46

White Noise 47

Noise-Equivalent Bandwidth (NEDΔf) 48

Shot Noise 50

Signal-to-Noise Ratio: Detector and BLIP Limits 51

Generation-Recombination Noise 52

Johnson Noise 53

1/f Noise and Temperature Noise 54

Detector Responsivity 55

Spectral Responsivity 57

Blackbody Responsivity 58

Noise-Equivalent Power 59

Specific or Normalized Detectivity 60

Photovoltaic Detectors or Photodiodes 61

Sources of Noise in PV Detectors 62

Expressions for D*PV,BLIP, D**PV,BLIP, and D* PV,JOLI 63

Photoconductive Detectors 64

Sources of Noise in PC Detectors 65

Third-Generation Infrared Imagers 66

Indium Antimonite (InSb) Photodiodes 67

Mercury Cadmium Telluride (HgCdTe) Photodetectors 68

Control of the Alloy Composition 69

HgCdTe Photodiodes and FPAs 70

DLHJ Photodiodes 71

Dual-Band HgCdTe FPAs 72

HDVIP Photodiodes 73

Uncooled HgCdTe Photodiodes 75

Quantum Well Infrared Photodetectors (QWIPs) 77

Types of QWIPs 80

Superlattices (SLs) 82

Multispectral QWIPs 83

Light Couplers 85

Pyroelectric Detectors 88

Pyroelectric Detectors—Mathematical Approach 90

Microbolometers 93

Microbolometers—Mathematical Approach 96

Infrared Dynamic Scene Simulators 99

Thermoelectric Detectors 100

Infrared Systems 101

Raster Scan Format: Single-Detector 101

Multiple-Detector Scan Formats: Serial Scene Dissection 103

Multiple-Detector Scan Formats: Parallel Scene Dissection 104

Staring Systems 105

Search Systems and Range Equation 106

Noise-Equivalent Irradiance 109

Performance Specification: Thermal-Imaging Systems 110

Modulation Transfer Function (MTF) Definitions 111

Optics MTF: Calculations 114

Electronics MTF: Calculations 116

MTF Measurement Setup and Sampling Effects 117

MTF Measurement Techniques: PSF and LSF 118

MTF Measurement Techniques: ESF and CTF 119

MTF Measurement Techniques: Noiselike Targets 121

MTF Measurement Techniques: Interferometry 123

Noise-Equivalent Temperature Difference (NETD) 124

NETD Measurement Technique 125

Minimum Resolvable Temperature Difference (MRTD) 126

MRTD: Calculation 127

MRTD Measurement Technique 128

MRTD Measurement: Automatic Test 129

Johnson Metric Methodology 130

Johnson Criteria Flaws 132

Targeting Task Performance (TTP) Metric Methodology 133

Human Vision—Distribution of Retinal Photoreceptors 134

Contrast Threshold Function (CTF) 136

Target Acquisition Performance 141

Probability of Task Performance 144

N50 to V50 Conversion (Example) 146

Acquisition Level Definitions 147

TTP Summary 148

Equation Summary 149

Bibliography 163

Index 167

Glossary

A

Area

Ad

Detector area

Aenp

Area of an entrance pupil

Aexp

Area of an exit pupil

Afootprint

Footprint area

Aimg

Area of an image

Alens

Lens area

Aobj

Area of an object

Aopt

Area of an optical component

As

Source area

AMTIR

Amorphous materials transmitting infrared radiation

ATR

Automatic target recognition

B

3-db bandwidth

B-B

Bound-to-bound

B-C

Bound-to-continuum

B-QB

Bound-to-quasi-bound

b.f.l

Back focal length

BLIP

Background-limited infrared photodetector

c

Speed of light in vacuum

Cd

Detector capacitance

Cth

Thermal capacitance

CQWIP

Corrugated quantum well infrared photodetector

CTF

Contrast transfer function

CTFeye

Contrast threshold function of the eye

CTFn

Contrast threshold function in the presence of external noise

CTFsys

Contrast threshold function of a system

CVD

Chemical vapor deposition

ddiff

Diameter of a diffraction-limited spot

D

Electrical displacement

D*

Normalized detectivity of a detector

D*BF

Background fluctuation D-star

D*BLIP

D-star under BLIP conditions

D*TF

Temperature fluctuation D-star

D**

Angle-normalized detectivity

Denp

Diameter of an entrance pupil

Dexp

Diameter of an exit pupil

Dimg

Image diameter

Din

Input diameter

Dlens

Lens diameter

Dobj

Object diameter

Dopt

Optics diameter

Dout

Output diameter

DDCA

Detector-Dewar cooler assembly

DEE

Digital emitter engine

DLHJ

Double-layer heterostructure junction

DSS

Dynamic scene simulator

e

Energy-based unit subscript

Ebkg

Background irradiance

Eimg

Image irradiance

Esource

Source irradiance

EAPD

Electron-injected avalanche photodiode

ESF

Edge spread function

𝛆

Energy of a photon

𝛆gap

Energy gap of a semiconductor material

f

Focal length

feff

Effective focal length

f0

Center frequency of an electrical filter

f.f.l

Front focal length

f(x,y)

Object function

FB

Back focal point

FF

Front focal point

F(ξ,η)

Object spectrum

FOR

Field of regard

FOV

Full-angle field of view

FOVhalf-angle

Half-angle field of view

FPA

Focal plane array

F/#

F-number

g(x,y)

Image function

G

Gain of a photoconductive detector

G(ξ,η)

Image spectrum

GASIR

Germanium arsenic selenium infrared material

h

Planck’s constant

himg

Image height

hobj

Object height

h(x,y)

Impulse response

H

Heat capacity

H(ξ,η)

Transfer function

HDVIP

High-density vertically integrated photodiode

HIFOV

Horizontal instantaneous field of view

HFOV

Horizontal field of view

i

Electrical current

i¯

Mean current

i1/f

rms 1/f-noise current

iavg

Average electrical current

ibkg

Background rms current

idark

Dark current

ij

rms Johnson noise current

iG/R

Generation-recombination noise rms current

inoise

Noise current

io

Dark current

ioc

Open circuit current

ipa

Preamplifier noise rms current

iph

Photogenerated current

irms

rms current

isc

Short-circuit current

ishot

Shot noise rms current

isig

Signal current

IC

Integrated circuit

IRFPA

Infrared focal plane array

J

Current density

k

Boltzmann’s constant

K

Thermal conductance

𝓚(ξt)

Spatial-frequency dependant MRTD proportionality factor

lw

Width of a well

L

Radiance

Lbkg

Background radiance

Lv

Visual luminance

Lλ

Spectral radiance

LPE

Liquid phase epitaxy

LSF

Line spread function

LWIR

Long-wave infrared

M

Exitance

Mmeas

Measured exitance

Mobj

Exitance of an object

Mλ

Spectral exitance

MBE

Molecular beam epitaxy

MEMS

Micro-electro-mechanical systems

MQW

Multiple quantum well

MRTD

Minimum resolvable temperature difference

MTF

Modulation transfer function

MTFpre

Pre-sampled MTF (optics detector, and line-of-sight jitter)

MTFd

Detector MTF

MTFpost

Post-sampled MTF (display, digital processing, and the eye-brain filter)

MTFsys

System’s MTF

MWIR

Midwave infrared

m*e

Effective mass of an electron

Magnification

ang

Angular magnification

n

Refractive index

ncycles

Number of cycles to discriminate a target

nd

Number of detectors

ne

Number of photogenerated electrons

nlines

Number of lines

NEI

Noise-equivalent irradiance

NEP

Noise-equivalent power

NEΔf

Noise-equivalent bandwidth

OTF

Optical transfer function

p

Object distance

p

Pyroelectric coefficient

p

Momentum of an electron

P

Magnitude of internal polarization

Pavg

Average power

Pchance

Probability of chance

Pmeasured

Field-measured probability

Pobserver

Observer’s probability

PC

Photocurrent

PSD

Power spectral density

PSF

Point spread function

PV

Photovoltaic or photodiode

q

Image distance

QW

Quantum well

QWIP

Quantum well infrared photodetector

R

Resistance

Rd

Detector resistance

Req

Equivalent resistance

Rin

Input resistance

RL

Load resistance

Rout

Output resistance

Rth

Thermal Resistance

RIIC

Read-in integrated circuit

ROIC

Read-out integrated circuit

𝓡

Responsivity

𝓡i

Current responsivity

𝓡v

Voltage responsivity

𝓡(λ)

Spectral responsivity

𝓡(T)

Blackbody responsivity

SCNtmp

Scene contrast temperature

SL

Superlattices

SNR

Signal-to-noise ratio

SR

Strehl-intensity ratio

SSRout

Out-of-band spurious response ratio

t

Time

T

Temperature

TB

Brightness temperature

Tbkg

Background temperature

TC

Color temperature

TCurie

Curie temperature

Td

Detector temperature

Tload

Load temperature

Trad

Radiation temperature

Tsource

Source temperature

Ttarget

Target temperature

TDMI

Time-division-multiplexed integration

TIR

Total internal reflection

TLHJ

Triple-layer heterostructure junction

TTP

Targeting task performance metric

TTPF

Target transfer probability function

υin

Input voltage

υj

Johnson noise rms voltage

υn

rms noise voltage

υoc

Open-circuit voltage

υout

Output voltage

υs

Shot-noise rms voltage

υsc

Short-circuit voltage

υscan

Scan velocity

υsig

Signal voltage

υ¯

Mean voltage

V

Abbe number

VIFOV

Vertical instantaneous field of view

VFOV

Vertical field of view

w.jpg

proportionality factor

x

Alloy composition or molar fraction ratio

α

Thermal resistance coefficient

α

Coefficient of absorption

β

Blur angle caused by diffraction

Δf

Electronic frequency bandwidth

Δt

Time interval

ΔT

Temperature difference

Δλ

Wavelength interval

ε

Emissivity

εo

Permeability of a material

η

Quantum efficiency

ηscan

Scan efficiency

η

Spatial frequency in the vertical direction

θ

Angle variable

θmax

Maximum angle subtense

Θ

Seebeck coefficient

λ

Wavelength

λcut

Cutoff wavelength

λmax

Maximum wavelength

λmax-cont

Maximum contrast wavelength

λpeak

Peak wavelength

λo

Fixed wavelength

Λ

The de Broglie wavelength

µ

Vertical sample frequency

ν

Optical frequency

ξ

Spatial frequency in the horizontal direction

ξcutoff

Spatial cutoff frequency

ξJ

Johnson spatial frequency

ρ

Electric charge

ρ

Reflectance

σ

Standard deviation

σ2

Variance

σe

Stefan-Boltzmann constant in energy units

σeye

rms visual noise expressed at a display

σn

rms noise filtered on by a display

σp

Stefan-Boltzmann constant in photon units

τ

Transmittance

τatm

Atmospheric transmittance

τdwell

Dwell time

τext

External transmittance

τframe

Frame time

τint

Internal transmittance

τline

Line time

τopt

Optical transmittance

τRC

Electrical time constant

τth

Thermal time constant

υ

Horizontal sample frequency

ϕ

Flux

ϕabs

Absorbed flux

ϕbkg

Background flux

ϕd

Detector flux

ϕimg

Flux incident on an image

ϕinc

Incident flux

ϕobj

Flux radiated by an object

ϕsig

Signal flux

ϕtrans

Transmitted flux

ϕλ

Spectral flux

ψ

Eigenfunction

ω

Angular frequency

Ω

Solid angle

Ωd

Detector solid angle

Ωbkg

Background solid angle

Ωexp

Exit pupil solid angle

Ωenp

Entrance pupil solid angle

Ωimg

Image solid angle

Ωlens

Lens solid angle

Ωobj

Object solid angle

Ωs

Source solid angle

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