詳細

Stray light is defined as unwanted light in an optical system, a familiar concept for anyone who has taken a photograph with the sun in or near their camera's field of view. In a low-cost consumer camera, stray light may be only a minor annoyance, but in a space-based telescope, it can result in the loss of data worth millions of dollars. It is imperative that optical system designers understand its consequences on system performance and adapt the design process to control it.

This book addresses stray light terminology, radiometry, and the physics of stray light mechanisms, such as surface roughness scatter and ghost reflections. The most-efficient ways of using stray light analysis software packages are included. The book also demonstrates how the basic principles are applied in the design, fabrication, and testing phases of optical system development.

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Errata (PDF)

Chapter 1 Introduction and Terminology
　1.1 Book Prerequities
　1.2 Book Organization
　1.3 Stray Light Terminology
　　1.3.1 Stray light paths
　　1.3.2 Specular and scatter stray light mechanisms
　　1.3.3 Critical and illuminated surfaces
　　1.3.4 In-field and out-of-field stray light
　　1.3.5 Internal and external stray light
　　1.3.6 "Move it or Block it or Paint/coat it or Clean it"
　1.4 Summary
Chapter 2 Basic Radiometry for Stray Light Analysis
　2.1 Radiometric Terms
　　2.1.1 Flux, or power, and radiometric versus photometric units
　　2.1.2 Reflectance, transmittance, and absorption
　　2.1.3 Solid angle and projected solid angle
　　2.1.4 Radiance
　　2.1.5 Blackbody radiance
　　2.1.6 Throughput
　　2.1.7 Intensity
　　2.1.8 Exitance
　　2.1.9 Irradiance
　　2.1.10 Bidirectional scattering distribution function
　2.2 Radiative Transfer
　　2.2.1 Point source transmittance
　　2.2.2 Detector field of view
　　2.2.3 Veiling glare index
　　2.2.4 Exclusion angle
　　2.2.5 Estimation of stray light using basic radiative transfer
　　2.2.6 Uncertainty of stray light estimates
　2.3 Detector Responsivity
　　2.3.1 Noise equivalent irradiance
　　2.3.2 Noise equivalent delta temperature
　2.4 Summary
Chapter 3 Basic Ray Tracing for Stray Light Analysis
　3.1 Building the Stray Light Model
　　3.1.1 Defining optical and mechanical geometry
　　3.1.2 Defining optical properties
　3.2 Ray Tracing
　　3.2.1 Using ray statistics to quantify speed of convergence
　　3.2.2 Aiming scattered rays to increase the speed of convergence
　　3.2.3 Backward ray tracing
　　3.2.4 Finding stray light paths using detector FOV
　　3.2.5 Determining critical and illuminated surfaces
　　3.2.6 Performing internal stray light calculations
　　3.2.7 Controlling ray ancestry to increase speed of convergence
　　3.2.8 Using Monte Carlo ray splitting increase speed of convergence
　　3.2.9 Calculating the effect of stray light on modulation transfer function
　3.3 Summary
Chapter 4 Scattering from Optical Surface Roughness and Coatings
　4.1 Scattering from Uncoated Optical Surface Roughness
　　4.1.1 BSDF from RMS surface roughness
　　4.1.2 BSDF from PSD
　　4.1.3 BSDF from empirical fits to measured data
　　4.1.4 Artifacts from roughness scatter
　4.2 Scattering from Coated Optical Surface Roughness
　4.3 Scattering from Scratches and Digs
　4.4 Summary
Chapter 5 Scattering from Particulate Contaminants
　5.1 Scattering from Spherical Particles (Mie Scatter Theory)
　5.2 Particle Density Function Models
　　5.2.1 The IEST CC1246D cleanliness standard
　　5.2.2 Measured (tabulated) distribution
　　5.2.3 Determining the particle density function using typical cleanliness levels, fallout rates, or direct measurement
　5.3 BSDF Models
　　5.3.1 BSDF from PAC
　　5.3.2 BSDF from Mie scatter calculations
　　5.3.3 BSDF from empirical fits to measured data
　　5.3.4 Determining the uncertainty in BSDF from the uncertainty in particle density function
　　5.3.5 Artifacts from contamination scatter
　5.4 Comparison of Scatter from Contaminants and Scatter from Surface Roughness
　5.5 Scattering from Inclusions in Bulk Media
　5.6 Molecular Contamination
　5.7 Summary
Chapter 6 Scattering from Black Surface Treatments
　6.1 Scattering from Black Surface Treatments
　　6.1.1 BRDF from empirical fits to measured data
　　6.1.2 Using published BRDF data
　　6.1.3 Artifacts from black surface treatment scatter
　6.2 Selection Criteria for Black Surface Treatments
　　6.2.1 Absorption in the sensor waveband
　　6.2.2 Specularity at high AOIs
　　6.2.3 Particulate contamination
　　6.2.4 Molecular contamination
　　6.2.5 Conductivity
　6.3 Types of Black Surface Treatments
　　6.3.1 Appliques
　　6.3.2 Treatments that reduce surface thickness
　　6.3.3 Treatments that increase surface thickness
　　　6.3.3.1 Painting
　　　6.3.3.2 Fused powders
　　　6.3.3.3 Black oxide coatings
　　　6.3.3.4 Anodize
　6.4 Survey of Widely Used Black Surface Treatments
　6.5 Summary
Chapter 7 Ghost Reflections, Aperture Diffraction, and Diffraction from Diffractive Optical Elements
　7.1 Ghost Reflections
　　7.1.1 Reflectance of uncoated and coated surfaces
　　　7.1.1.1 Uncoated surfaces
　　　7.1.1.2 Coated surfaces
　　7.1.2 Reflectance from typical values
　　7.1.3 Reflectance from the stack definition or predicted performance data
　　7.1.4 Reflectance from measured data
　　7.1.5 Artifacts from ghost reflections
　　7.1.6 "Reflective" ghosts
　7.2 Aperture Diffraction
　　7.2.1 Aperture diffraction theory
　　7.2.2 Calculation of aperture diffraction in stray light analysis programs
　　7.2.3 Artifacts from aperture diffraction
　　7.2.4 Expressions for wide-angle diffraction calculations
　7.3 Diffraction from Diffractive Optical Elements
　　7.3.1 DOE diffraction theory
　　7.3.2 Artifacts from DOE diffraction
　　7.3.3 Scattering from DOE transition regions
　7.4 Summary
Chapter 8 Optical Design for Stray Light Control
　8.1 Use a Field Stop
　8.2 Use an Unobscured Optical Design
　8.3 Minimize the Number of Optical Elements between the Aperture Stop and the Focal Plane
　8.4 Use a Lyot Stop
　　8.4.1 Calculating Lyot stop diameter from analytic expressions
　　8.4.2 Calculating Lyot stop diameter from coherent beam analysis
　8.5 Use a Pupil Mask to Block Diffraction and Scattering from Struts and Other Obscurations
　8.6 Minimize Illumination of the Aperture Stop
　8.7 Minimize the Number of Optical Elements, Especially Refractive Elements
　8.8 Avoid Optical Elements at Intermediate Images
　8.9 Avoid Ghosts Focused at the Focal Plane
　8.10 Minimize Vignetting, Including the Projected Solid Angle of Struts
　8.11 Use Temporal, Spectral, or Polarization Filters
　8.12 Use Nonuniformity Compensation and Reflective Warm Shields in IR Systems
　8.13 Summary
Chapter 9 Baffle and Cold Shield Design
　9.1 Design of the Main Baffles and Cold Shields
　9.2 Design of Vanes for Main Baffles and Cold Shields
　　9.2.1 Optimal aperture diameter, depth, and spacing for baffle vanes
　　9.2.2 Edge radius, bevel angle, and angle for baffle vanes
　　9.2.3 Groove-shaped baffle vanes
　9.3 Design of Baffles for Cassegrain-Type Systems
　9.4 Design of Reflective Baffle Vanes
　9.5 Design of Masks
　9.6 Summary
Chapter 10 Measurement of BSDF, TIS, and System Stray Light
　10.1 Measurement of BSDF (Scatterometers)
　10.2 Measurement of TIS
　10.3 Measurement of System Stray Light
　　10.3.1 Sensor radiometric calibration
　　10.3.2 Collimated source test
　　10.3.3 Extended source test
　　10.3.4 Solar tests
　　　10.3.4.1 Using direct sunlight
　　　10.3.4.2 Using a heliostat
　10.4 Internal Stray Light Testing
　10.5 Summary
Chapter 11 Stray Light Engineering Process
　11.1 Define Stray Light Requirements
　　11.1.1 Maximum allowed image plane irradiance and exclusion angle
　　11.1.2 Inheritance of stray light requirements from comparable systems
　11.2 Design Optics, Pick Surface Roughness, Contamination Levels, and Coatings
　11.3 Build Stray Light Model, Add Baffles and Black Surface Treatments
　11.4 Compute Stray Light Performance
　11.5 Build and Test
　11.6 Process Completion
　11.7 Summary
　11.8 Guidelines and Rules of Thumb