Optical Spectroscopy with
Basics - Building Blocks - Systems - Applications
Basics 2: Spectrometer Basics, Concepts, and
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of the BASICS pages is available in printed shape since June 2014:
"Fundamentals of dispersive optical Spectroscopy
SPIE-Monograph, ISBN No.: 9780819498243
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Aim of the “Fundamentals” is to help starters with the definition and verification of the instrumentation for optical spectroscopy. Experienced spectroscopists and expert physicists will know some of the issues better and in deeper detail. But hopefully, every reader may find things worth mentioning. If any statement will be found not well explained or misleading, please write an e-mail to the address provided in the “Contact” page.
It is the aim of “Basics“, to help the user with the justification of opto-spectroscopical instrumentation. The basics describe parameters and their association. Experienced spectroscopists and experts of the special physics will know details better and deeper, but hopefully, every reader may find useful information anyway.
2.1.1 The basic principle of a spectrometer
Graph 11, the components of a spectrometer for flexible use:
2.1.2 Attributes of modular spectrometers
Several basic spectrometer concepts exist, we look them up.
2.2.1 The Littrow configuration
Graph 12, the Littrow mount seen from top
Graph 13: Littrow configuration seen from the side and the front, having entrance and exit atop of each other.
2.2.2 Area correction by equation F13 :
2.2.3 Advantages and disadvantages of the Littrow
2.3.1 The Ebert-Fastie configuration
Graph 14, Ebert-Fastie setup seen from top
2.3.2 Ebert-Fastie area correction equation F14 :
2.3.2 Curved slits
2.4.0 The Czerny-Turner configuration
Graph 15: The Czerny-Turner spectrometer and its angles
188.8.131.52 The median angle at the grating of Ebert-Fastie- and Czerny-Turner-configurations
2.4.1 Imaging field corrections
2.4.6 The influence of the internal angles on the wavelength
2.5.1 Spectrometers for the Vacuum range
Graph 16: Spectrometer concepts for the Vacuum range
2.5.2 Normal Incidence (NI)
2.5.4 Grazing Incidence
2.6.1 Grating rotation and actuation
2.6.2 Direction of the grating rotation
2.6.3 The driving system
Graph 17: The classical “sine-drive“
2.6.4 Grating position versus rotation
Graph 18: Influence of the grating rotation on the active surface
2.6.5 Grating actuation and steering are further described in Application C1.
2.7.0 Aperture and light flux (luminosity)
2.7.1 Real Aperture or f-number?
2.7.2 Examples on the influence of the internal angles on the light flux
2.7.5 Comparing the calculations of f-number vs W by light flux/luminosity
The illustration of f-number in comparison with W.
Graphically supported description of equation F17:
Graph L: The luminosity at the spectrometer output by F17(new)
2.7.6 Monochromator examples
2.7.7 Spectrograph examples
2.8.1 The Dispersion
Graph 2A: the angles at the grating in a real spectrometer
2.9.1 Intensity distribution in the exit
Graph 19A. Intensity distribution in the exit / slit function
Graph 19B: Transfer Function and Distribution of the optical Power over the exit Slit.
2.10.1 Spectral resolution
Graph 20: Spectral resolution by the 50% criterion
Graph 21: Spectral resolution by the 50% rule, and peaks of different amplitude
2.10.2 Does one measure the resolution of the spectrometer, or that of the experiment?
2.10.3 When is a spectral curve completely reproduced?
Graph 22: Situation of adjacent 22 or 23 data points to provide a Gaussian fit of a peak which is much wider then the bandwidth BW of the spectrometer.
2.10.4 The Raleigh Diffraction Limit
2.10.5 Resolution of a monochromator compared to a spectrograph
Graph 23: Peak reconstruction by a monochromator, if the line is finer than the instrument´s bandwidth, FWHM resolution is about 2.2 bandwidths
Graph 24: Peak reconstruction by a spectrograph, if the line is finer than the instrument´s bandwidth, FWHM resolution is at least 3 pixels = 3 bandwidths
2.10.6 Numerical resolution Rp and Rr, and their wavelength dependence
2.10.7 A practical example on the optimization of resolution
2.10.8 Experimental examples on spectral resolution
Graph 25: Typical resolution data, recorded by monochromators of different focal length. The darts in the graph refer to the notes in the description following
2.11.1 The image quality (Q-Factor or Fidelity)
2.11.2 What are the trouble makers in image transfer?
Graph 26A the most common distortions (aberrations) in spectrometers with laterally opened angles
Graph 26B: Transfer function and stigmatic / astigmatic reproduction
2.11.5 Toroidal transfer systems
2.11.6 General aberrations and Coma
Graph 27: Coma effects
Graph 28: Example of spectral falsification from the Coma effect
2.12.1 False light, stray light, and contrast
2.12.4 The contrast ratio C, describing useful signal versus destructive signal
Graph 29: Typical behaviour of the three main disturbances
2.13.1 Double pass, Double and Triple spectrometers
2.13.2 The double pass spectrometer
Graph 30: Beam configuration of a double pass spectrometer
2.13.3 Double spectrometers
2.13.4 Subtractive spectrometers
Graph 31: Typical double spectrometer setup, offering additive or subtractive operation
2.14.1 Efficiency behaviour and analysis
2.14.2 Energy transmission and Bandwdith of single, double, and triple stage Spectrometers
Graph 31A shows, how the energy transmission vs slit position changes with the number of stages
2.14.3 Effects of Photon travelling Time (Time of
Graph 31B describes the dispersion of travelling time, and the reduction of beam homogeneity, both versus the Aperture
2.15.1 Stability and thermal influence
2.15.2 Suggestions to minimize environmental influence
2.16.1 Reduction of unwanted spectral orders, and other filtering
2.16.2 Long pass filters
Graph 32: Typical order sorting filter curves (long pass filters) in the UV-Vis
2.16.3 Bandpass filters and prism
Graph 33 Typical transfer curves of bandpass filters, short pass filter, prism
2.16.4 Short pass filters
2.16.5 Echelle grating applications
2.16.6 The dispersion of a prism spectrometer
Graph 34: Reciprocal dispersion of a quartz prism with 30° angle, working in a spectrometer of 100 mm focal length.
2.17.1 Light transfer by optical fibres
2.18.1 General collection of performance parameters of spectrometers, and conclusion
Graph 35: Collection of the most important spectrometer parameters
Hoping the study of the book Elements of dispersive optical Spectrometers will be of help for you, we remain with special thanks for your interest.
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Spectroscopy with dispersive Spectrometers
Basics - Building Blocks - Systems - Applications " are reserved by
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Status April 2012