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Spie Press Book

Fundamentals of Dispersive Optical Spectroscopy Systems
Author(s): Wilfried Neumann
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Book Description

Bridging the gap between basic theoretical texts and specific system recommendations, Fundamentals of Dispersive Optical Spectroscopy Systems addresses the definition, design, justification, and verification of instrumentation for optical spectroscopy, with an emphasis on the application and realization of the technology. The optical spectroscopy solutions discussed within use dispersive spectrometers that primarily involve diffraction gratings. Topics include dispersive elements, detectors, illumination, calibration, and stray light. This book is suitable for students and for professionals looking for a comprehensive text that compares theoretical designs and physical reality during installation.

Book Details

Date Published: 23 June 2014
Pages: 296
ISBN: 9780819498243
Volume: PM242
Errata

Table of Contents
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Table of Contents

Preface

1 Introduction, Terminology, and Scales
1.1 General Introduction
1.2 Photon Energies
1.3 Photon-Energy Conversion Equations
1.4 Naming Convention
1.5 The Spectral Line
1.6 General Rule of Optical Transfer
1.7 Definitions
      1.7.1 Exponential functions and signal damping (attenuation)
      1.7.2 Low-pass filter functions
      1.7.3 Definition of bandwidth in electric versus optical spectroscopy systems
1.8 Spectral Distribution of Thermal Radiation by Planck's Law
1.9 Keeping Optics Clean
References

2 Spectrometer Concepts
2.1 Basic Principle of an Optical Spectrometer
      2.1.1 Attributes of modular spectrometers
2.2 Basic Grating Parameters and Functions
      2.2.1 The free spectral range
      2.2.2 Dispersion of gratings and prisms
2.3 Existing Basic-Spectrometer Concepts
      2.3.1 The Littrow configuration
      2.3.2 Ebert-Fastie configuration
      2.3.3 Czerny-Turner configuration
2.4 Impacts and Distortions to Spectrometers
      2.4.1 The influence of the internal angles on the wavelength
2.5 Other Spectrometers, Including Those for the Vacuum Range
      2.5.1 Curved-grating spectrometer: Wadsworth setup
      2.5.2 Normal incidence
      2.5.3 Seya-Namioka
      2.5.4 Grazing incidence
      2.5.5 Rowland circle spectrometer and Paschen-Runge mount
2.6 Other Parameters and Design Features
      2.6.1 Straight slits versus curved slits
      2.6.2 Aperture and light flux (luminosity)
      2.6.3 Dispersion of spectrometers
      2.6.4 Intensity distribution in the exit
      2.6.5 Spectral resolution
      2.6.6 Image quality: Q-factor or fidelity
      2.6.7 False and stray light, and contrast
      2.6.8 Contrast ratio C
2.7 Mechanical Stability and Thermal Influence
      2.7.1 Measuring thermal variations
      2.7.2 Defocusing effects
      2.7.3 Typical thermal constants
      2.7.4 Minimizing environmental influence
2.8 Reduction of Unwanted Spectral Orders, and Other Filtering
      2.8.1 Long-pass filters
      2.8.2 Band-pass filters and prism
      2.8.3 Short-pass filters
      2.8.4 General filtering techniques
      2.8.5 Notch filters
2.9 General Collection of Performance Parameters of Spectrometers
Reference

3 The Dispersion Elements: Diffraction Grating and Refraction Prism
3.1 Introduction
3.2 Diffraction Efficiencies and Polarization of Standard Gratings
3.3 Types of Dispersers
      3.3.1 Holographic gratings
      3.3.2 Echelle gratings
      3.3.3 Concave and other curved gratings
      3.3.4 Transmission gratings
3.4 The Prism
3.5 The Grism
3.6 Other Features of Diffraction Gratings
      3.6.1 Polarization anomaly
      3.6.2 Polarization of Echelle gratings
      3.6.3 Scattering effects
      3.6.4 Grating ghosts
      3.6.5 Shadowing and diffusion
      3.6.6 Surface coating
References

4 Design Considerations of Monochromator and Spectrograph Systems
4.1 Beam Travel inside a Spectrometer
      4.1.1 Beam travel in a symmetric spectrometer
      4.1.2 Variations of the basic Ebert-Fastie and Czerny-Turner concepts
      4.1.3 Output wavelength as a function of the source position
      4.1.4 Local output dispersion as a function of the lateral position in the field output
      4.1.5 Output dispersion and fidelity as a function of the tilt angle of the field output
      4.1.6 Correction methods for spectral imaging
      4.1.7 Prism spectrometer
      4.1.8 Dispersion of a prism spectrometer
      4.1.9 Echelle grating spectrometers
      4.1.10 Transmission spectrometers
4.2 Grating Rotation and Actuation
      4.2.1 Classical driving system
      4.2.2 Grating actuation by a rotating system
4.3 Multiple-Stage Spectrometers
      4.3.1 Double-pass spectrometers
      4.3.2 Double spectrometers
      4.3.3 Construction considerations for double spectrometers
      4.3.4 Various configurations of flexible double spectrometers
      4.3.5 General performance data of double spectrometers versus similar single-stage systems
      4.3.6 Triple-stage spectrometers
4.4 Echelle Spectrometers
      4.4.1 Echelle monochromators and 1D spectrographs
      4.4.2 High-resolution Echelle spectrometer designed as a monochromator and 1D spectrograph
      4.4.3 Two-dimensional Echelle spectrometer for the parallel recovery of wide wavelength ranges at high resolution
4.5 Hyperspectral Imaging
      4.5.1 Internal references
      4.5.2 Example of hyperspectral imaging
      4.5.3 General design for hyperspectral imaging
References

5 Detectors for Optical Spectroscopy
5.1 Introduction
      5.1.1 Work and power of light signals
      5.1.2 Basic parameters of detectors
      5.1.3 Detection limit, noise, and SNR
      5.1.4 Detection limit, noise, and SNR in absolute measurements
      5.1.5 Detection limit, noise, and SNR in relative measurements
5.2 Single-Point Detectors
      5.2.1 Phototubes
      5.2.2 Comments on the interpretation of PMT data sheets
      5.2.3 A sample calculation for PMTs, valid for an integration time of 1 s
      5.2.4 Photon counter
      5.2.5 UV PMTs and scintillators
5.3 Illumination of Detectors, Combined with Image Conversion
5.4 Channeltron and Microchannel Plate
5.5 Intensified PMT and Single-Photon Counting
5.6 Solid State Detectors
      5.6.1 General effect of cooling
      5.6.2 Planck's radiation equals blackbody radiation
      5.6.3 Detectors and the ambient temperature
      5.6.4 Tandem detectors
      5.6.5 Typical parameters of solid state detectors, and their interpretation
5.7 Design Considerations of Solid State Detectors
      5.7.1 Illumination of small detector elements
      5.7.2 Charge storage in semiconductor elements, thermal recombination, and holding time
      5.7.3 PIN and avalanche diodes
      5.7.4 Detector coupling by fiber optics
5.8 Area Detectors: CCDs and Arrays
      5.8.1 Mounting of area detectors, the resulting disturbance, and the distribution of wavelengths
      5.8.2 Basic parameters of arrays and CCDs with and without cooling
      5.8.3 Signal transfer and read-out
      5.8.4 CCD architectures
      5.8.5 CCD and array efficiency
      5.8.6 Time control: synchronization, shutter, and gating
      5.8.7 Current formats of area detectors
      5.8.8 Read-out techniques: Multi-spectra spectroscopy, binning, and virtual CCD partition
      5.8.9 CCDs and array systems with image intensification
      5.8.10 Data acquisition in the ms-ms time frame
      5.8.11 Extending the spectral efficiency into the deep UV
      5.8.12 NIR and IR area detectors
5.9 Other Area Detectors
      5.9.1 CID and CMOS arrays
      5.9.2 Position-sensitive detector plate
      5.9.3 Streak and framing camera
References

6 Illumination of Spectrometers and Samples: Light Sources, Transfer Systems, and Fiber Optics
6.1 Introduction and Representation of Symbols
6.2 Radiometric Parameters
6.3 Advantage of Using V and sr
6.4 Different Types of Radiation and Their Collection
      6.4.1 Laser radiation
      6.4.2 Cone-shaped radiation
      6.4.3 Ball-shaped radiation from point sources: Lamps
      6.4.4 Diffuse radiation collected by integrating spheres
      6.4.5 NIR radiation
      6.4.6 IR radiators
6.5 Examples of Optimizing Spectrometer Systems
      6.5.1 Optimization of gratings
      6.5.2 Change-over wavelengths of lamps, gratings, and detectors
6.6 End Result of an Illumination Monochromator System
6.7 Light Transfer and Coupling by Fiber Optics
      6.7.1 Fiber guides, light-wave guides, and fiber optics
      6.7.2 Fiber optics for the UV-Vis-NIR range
      6.7.3 Fiber optic parameters and effects
      6.7.4 "Flexible optical bench," and a precaution about its handling
      6.7.5 Typical kinds and variations of single fibers and fiber cables
6.8 Transfer Systems
      6.8.1 Coupling by bare optical fibers
      6.8.2 Coupling by lens systems
      6.8.3 Coupling by mirror systems
References

7 Calibration of Spectrometers
7.1 Calibration of the Axis of Dispersion, Wavelength, and Photon Energy
      7.1.1 Parameters that define the angular position of a dispersion element
      7.1.2 Driving a grating or prism spectrometer
      7.1.3 Grating spectrometers with a rotary drive
      7.1.4 Calibration of the field output
7.2 Calibrating the Axis of Intensity, Signal, and Illumination
      7.2.1 Requirements for a useful calibration and portability of data
      7.2.2 Light sources for radiometric calibration
      7.2.3 Procedures to produce reliable calibrated data
7.3 Transfer Efficiency of Spectrometers
      7.3.1 General behavior
      7.3.2 Measurement of transfer efficiency
References

8 Stray and False Light: Origin, Impact, and Analysis
8.1 Origin of Stray Light
8.2 Impact of Stray Light
      8.2.1 Disturbance in the application of discrete spectral signals
      8.2.2 Disturbance in the application of broadband spectral signals
8.3 Analysis and Quantization of Stray Light in Spectrometers and Spectrophotometers
8.4 Minimizing the Impact of Disturbance through Optimization
8.5 Reducing Stray Light
References

9 Related Techniques
9.1 Compact, Fiber-Optically-Coupled Spectrographs
9.2 Programmable Gratings
9.3 Bragg Gratings and Filters
9.4 Hadamard Spectrometer
      9.4.1 Principle of Hadamard measurements
      9.4.2 Hadamard setups
References


Preface

My search for universal and comprehensive literature on dispersive optical spectroscopy revealed many gaps. The books on very basic information are rather theoretical and dig deep into arithmetic derivations to calculate spectrometers, illumination, and detection. The books on the different applications of optical spectroscopy are mainly "cookbooks" and do not explain why something should be done in a certain way. Books with comprehensive content are available from the vendors of dispersers, spectrometers, detectors, and systems - they naturally feature the advantages of the supported products but offer no overall view.

For more than twenty years, I have calculated and delivered special dispersive spectroscopy systems for different applications. In the time between inquiry and decision, the customers wanted to justify my presentation and compare it. A common problem was finding useful references that could be used to verify my calculations and predictions. So, again and again, I wrote long letters combining the different parameters of the project presented. Several of my customers - industrial project managers as well as researchers - not only acknowledged the proposals but also often used the papers to check the instrumental performance at delivery. Because the proposals fit the requirements and the predictions were at least reached, their confidence was earned. Customers used my papers for internal documentation and teaching. Several asked me to provide the know-how in a general, written database in order to close the gap between theory, practice, and applications. After my retirement from regular work, I did just that, and published my writing on my homepage (www.spectra-magic.de). Now, the content has been improved and extended into a pair of printed books, the first of which you have now. The aim of this book is to supply students, scientists, and technicians entering the field of optical spectroscopy with a complete and comprehensive tutorial; to offer background knowledge, overview, and calculation details to system designers for reference purpose; and to provide an easy-to-read compendium for specialists familiar with the details of optical spectroscopy.

Acknowledgments

My thanks are first addressed to my wife, Heidi, for her patience during the many weeks spent investigating, reviewing, and writing. I also thank those who urged me to start writing at all and who collected data and calculations. The trigger to turn the homepage into written books came from Dr. Karl- Friedrich Klein, who kept me going and contacted SPIE. The section on fiber optics was supported by Joachim Mannhardt, who provided specifics and added features and ideas. After the manuscript was given to SPIE, external reviewers spent much effort on the content, providing corrections and suggestions for improvement; that valuable support came from Mr. Robert Jarratt and Dr. Alexander Sheeline. Last but not least, I'd like to thank Tim Lamkins, Scott McNeill, and Kerry McManus Eastwood at SPIE for the work they invested into the project.

I hope that readers will find useful details that further their interest or work.

Wilfried Neumann
April 2014


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