Fundamentals of Infrared Sensing

This book is an outgrowth of a short course that the author has presented for SPIE for the past 25 years or so on the fundamentals of infrared sensing. This field spans several technical disciplines, which can leave the beginner with the “where do I start?” question. The selection of the material included here represents those concepts and terminology that a newcomer in the field of infrared systems needs to understand. These include items that were initially confusing to the author, ones that he has found useful in practice, or concepts that are commonly misunderstood. These are explained in the simplest terms that keep the key ideas. The level of mathematics is generally algebra-based. The book contains sample calculations but does not include problem sets. This is a consequence of the book’s origin as a set of short course notes. It is not intended as a stand-alone college textbook but rather as a self-study reference for the beginning systems engineer. The intended audience is a person with a bachelor’s-level training in science or engineering. It is meant to be an introduction, with sufficient detail to enable the reader to make initial back-of-the-envelope calculations and to understand the basic tradeoffs and trends involved.

Table of Contents:
Preface 1 Introduction References 2 Geometrical Optics 2.1 Introduction 2.2 Imaging Concepts 2.3 Algebraic Rules for Image Formation 2.3.1 Point sources at infinity 2.4 Aperture Stop, Marginal Ray, and F-number 2.5 Field of View 2.6 Detector Footprint 2.7 Image Quality 2.7.1 Diffraction 2.7.2 Aberrations 2.7.3 Image-quality summary 2.8 Infrared Materials 2.9 Modulation Transfer Function 2.9.1 Spatial frequency 2.9.2 Modulation transfer function definition 2.9.3 MTF examples References Bibliography Radiometry 3.1 Introduction 3.1.1 Solid angle 3.1.1 Radiometric nomenclature and units 3.2 Irradiance and Exitance 3.3 Intensity 3.3.1 Inverse-square law for point sources 3.3.2 Irradiance on a tilted receiver 3.4 Radiance 3.4.1 Radiance example for a tilted receiver 3.4.2 Lambertian radiator 3.4.3 Nonzero view angles 3.4.4 Cosine-to-the-fourth falloff 3.4.5 Tilting a Lambertian source 3.4.6 Lambertian radiator: relation of exitance and radiance 3.5 Flux Transfer in Image-Forming Systems 3.5.1 Why is radiance analogous to perceived brightness? 3.5.2 Example calculation of image irradiance (extended source) 3.5.3 When to use a lens? 3.5.4 Cosine-to-the-fourth falloff in imaging systems 3.5.5 Irradiance depends on the image-space F-number 3.5.6 Aperture stop not at the lens 3.5.7 Radiance of an extended source is conserved 3.5.8 Dilution of radiance by a finite impulse response 3.6 Point-Source Imaging Bibliography 4 Thermal Sources 4.1 Introduction 4.2 Blackbody Radiation 4.3 Planck's Equation 4.3.1 Other forms of Planck's equation 4.3.2 Stefan–Boltzmann law 4.3.3 Wien's displacement law 4.3.4 Half-power points 4.3.5 Calculations 4.3.6 Planck's equation in terms of other spectral variables 4.4 Exitance Contrast 4.5 Emissivity 4.5.1 Kirchhoff's law 4.5.2 Graybody 4.5.3 Selective radiator 4.5.4 Emissivity of common materials 4.5.5 Emissivity as a function of ? and T References Bibliography 5 Detectors 5.1 Comparing Thermal Detectors and Photon Detectors 5.2 Responsivity 5.2.1 Spectral responsivity 5.2.2 Blackbody responsivity 5.2.3 Relating R(T) to R(?cut) 5.3 Cooling Requirements for Photon Detectors 5.4 Time Response and Frequency Response 5.5 Thermal Detectors 5.5.1 Temporal response 5.5.2 Bolometric sensors 5.5.3 Pyroelectric sensors 5.6 Photon Sensors 5.6.1 Photoconductive sensors 5.6.2 Photovoltaic mechanism 5.6.3 Schottky-barrier detectors Reference Bibliography 6 Temperature Measurement 6.1 Measurement Configurations 6.2 Radiation Temperature 6.3 Brightness Temperature 6.4 Color Temperature 6.5 Practical Temperature Measurements with an IR Camera Bibliography 7 Noise in the Detection Process 7.1 Basic Noise Nomenclature 7.2 Sources of Noise 7.3 Internally Generated Sensor Noise 7.4 Noise Power Spectral Density 7.5 Calculations with White Noise 7.6 Shot Noise 7.6.1 Development of the shot-noise expression 7.6.2 What process generates the current? 7.7 SNR in the Signal-Shot-Noise Limit 7.8 SNR in the Background-Shot-Noise Limit 7.9 Generation–Recombination Noise 7.10 Johnson Noise 7.10.1 Johnson-noise units 7.10.2 Johnson-noise calculation example: two parallel resistors at different temperatures 7.10.3 SNR in the Johnson-noise limit 7.10.4 Johnson noise root-area and root-bandwidth dependence 7.11 1/f Noise 7.12 Thermal-Fluctuation Noise References Bibliography 8 Detector Sensitivity Figures of Merit 8.1 Noise-Equivalent Power (NEP) 8.1.1 Numerical-calculation example with NEP 8.2 Normalized Detectivity D* 8.2.1 Numerical calculations with D* 8.2.2 Numerical calculations with D* 8.3 Background-Limited D* for Photon Sensors 8.4 Johnson-Noise-Limited (JOLI) D* for Photon Sensors 8.5 Temperature-Fluctuation-Noise-Limited D* for Thermal Sensors 8.6 Comparing the Performance of Thermal and Photon Sensors Reference Bibliography 9 Infrared Systems 9.1 General Comments 9.2 Scan Formats 9.2.1 Multiple-detector scan formats 9.3 Search System: Range Equation 9.3.1 Example of a search system preliminary design 9.4 Thermal Imager: NETD Expression 9.4.1 Calculation example for NETD 9.5 Minimum Resolvable Temperature Difference (MRTD) References Bibliography Index