Fundamentals of Dispersive Optical Spectroscopy Systems

Author(s): Wilfried Neumann

Published: 2014

PDF ISBN: 9780819498250 | Print ISBN: 9780819498243

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.

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Front Matter

CHAPTER 1.

Introduction, Terminology, and Scales

Chapter Outline +

CHAPTER 2.

Spectrometer Concepts

Chapter Outline +

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
2.3.2.1 Origin of astigmatism
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)
2.6.2.1 Real aperture or f-number?
2.6.2.2 Examples of the influence of the internal angles on the light flux
2.6.2.3 Calculating the f-number versus V for light flux/luminosity
2.6.3 Dispersion of spectrometers
2.6.4 Intensity distribution in the exit
2.6.5 Spectral resolution
2.6.5.1 Does one measure the resolution of the spectrometer or that of the experiment?
2.6.5.2 When is a spectral curve completely reproduced?
2.6.5.3 Rayleigh diffraction limit
2.6.5.4 Resolution of a monochromator compared to that of a spectrograph
2.6.5.5 Numerical resolution Rp and Rr, and their wavelength dependence
2.6.6 Image quality: Q-factor or fidelity
2.6.6.1 Calculating aberrations
2.6.6.2 A reflecting spectrometer has two or even three axes
2.6.6.3 The slit height also influences the total aberrations
2.6.6.4 The quality factor
2.6.6.5 Image-transfer issues
2.6.6.6 Spectrometers with internal image correction
2.6.6.7 General aberrations and coma
2.6.7 False and stray light, and contrast
2.6.7.1 Reducing stray light
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

CHAPTER 3.

The Dispersion Elements: Diffraction Grating and Refraction Prism

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CHAPTER 4.

Design Considerations of Monochromator and Spectrograph Systems

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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
4.1.6.1 External imaging correction
4.1.6.2 Internal imaging correction by toroidal mirrors
4.1.6.3 Internal imaging correction by a curved grating
4.1.6.4 Internal imaging correction by a Schmidt corrector
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
4.3.2.1 Subtractive spectrometers
4.3.2.2 Efficiency behavior and analysis
4.3.2.3 Energy transmission and bandwidth of single-, double-, and triple-stage spectrometers
4.3.2.4 Effects of photon traveling time (time of flight)
4.3.3 Construction considerations for double spectrometers
4.3.3.1 Additive setup
4.3.3.2 Subtractive setup
4.3.3.3 Modern off-axis double spectrometers
4.3.3.4 Mechanical filtering in 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
4.4.2.1 Echelle aberrations
4.4.2.2 Thermal drift assuming an aluminum chassis
4.4.3 Two-dimensional Echelle spectrometer for the parallel recovery of wide wavelength ranges at high resolution
4.4.3.1 Concept of a compact 2D Echelle
4.4.3.2 Comparison of an Ebert–Fastie and a folded Czerny–Turner
4.4.3.3 Constructive precautions
4.5 Hyperspectral Imaging
4.5.1 Internal references
4.5.2 Example of hyperspectral imaging
4.5.2.1 Image reproduction and spectral recovery
4.5.2.2 Overlaid hyperspectral image recovery
4.5.2.3 Separated hyperspectral image recording
4.5.2.4 Hyperspectral imaging supported by filters
4.5.3 General design for hyperspectral imaging
4.5.3.1 Design considerations
References

CHAPTER 5.

Detectors for Optical Spectroscopy

Chapter Outline +

5.1 Introduction
5.1.1 Work and power of light signals
5.1.2 Basic parameters of detectors
5.1.2.1 Pre-amplifier considerations and wiring
5.1.2.2 General signals and sources of noise in optical detector systems
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
5.6.3.1 Signal modulation and synchronized detection
5.6.3.2 Estimation of the modulated measurement
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
5.8.1.1 Popular versions of area detectors
5.8.2 Basic parameters of arrays and CCDs with and without cooling
5.8.2.1 Pixel size, capacity, sources of noise, dynamic range, shift times, read-out time, and ADC conversion time
5.8.2.2 Applicability of CCDs for spectroscopy, image processing, and photography
5.8.3 Signal transfer and read-out
5.8.3.1 Combining the read-out in imaging mode and the display in spectroscopy mode
5.8.4 CCD architectures
5.8.5 CCD and array efficiency
5.8.5.1 Front-illuminated CCDs
5.8.5.2 Rear-side-illuminated CCDs
5.8.5.3 Interference of rear-side-illuminated CCDs: Etaloning
5.8.6 Time control: synchronization, shutter, and gating
5.8.6.1 Shutter control
5.8.6.2 Microchannel-plate image intensifiers
5.8.7 Current formats of area detectors
5.8.8 Read-out techniques: Multi-spectra spectroscopy, binning, and virtual CCD partition
5.8.8.1 Virtual CCD programming
5.8.9 CCDs and array systems with image intensification
5.8.9.1 CCDs with on-chip multiplication or electron multiplication (EMCCD)
5.8.9.2 CCDs with an additional microchannel-plate image intensifier (MCP-CCD)
5.8.10 Data acquisition in the ms–ms time frame
5.8.10.1 Kinetic measurements
5.8.10.2 Double-pulse measurements
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
5.9.1.1 Typical CMOS parameters, and comparison to CCDs
5.9.2 Position-sensitive detector plate
5.9.3 Streak and framing camera
References