Optical Spectroscopy with dispersive Spectrometers
Basics - Building Blocks - Systems - Applications

Basics 3: Common Configurations of
Monochromator and Spectrograph Systems

 

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"Fundamentals of dispersive optical Spectrometers",
SPIE-Monograph, ISBN No.: 9780819498243

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3.0.0 Fundamentals
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.


3.0.1 Overlook, Conversion Factors, Equations
3.0.2 This site consists of 4 parts:
1) the spectrometer configurations of single and multiple stage systems,
2) Echelle spectrometer configurations,
3) basic Prism spectrometers,
4) basic transmission spectrometers.

3.1.0 Introduction and Nomenclature


3.1.1 Beam travel versions of flexible Spectrometers
3.1.1 Beam configuration of Ebert-Fastie or Czerny-Turner spectrometers

Graph 51 CT grating turning towrds entrance

Graph 51: Czerny-Turner, the grating turns towards the entrance. In an Ebert-Fastie the rays travel similar.

Graph 52 CT grating turning towrds exit
Graph 52: Czerny-Turner, the grating turns towards the exit. In an Ebert-Fastie the rays travel similar.


3.1.2 Beam travel in a (close to) symmetric spectrometer

Graph 31 CT corrected efficiently used mirror area
Graph 53 makes clear, that the field output has a restricted area of full illumination.

Graph 54 Signal amplitude disptribution in the field output
Graph 54: The typical intensity distribution over the horizontal width of the field.  

3.1.3 Variations of the basic Ebert-Fastie and Czerny-Turner concepts, and multiple gratings mounted
versus single gratings

3.1.3.1 the front entrance and exit will be mounted oblique to the wall, as shown in graph 55
Graph 55 Oblique Czerny Turner
Graph 55:
General beam travel in an oblique Czerny-Turner spectrometer, also named W configuration.
3.1.3.2 Single grating configuration.
3.1.3.3 Triple grating configuration, version to pivot on the centre of the table
3.1.3.4 Triple grating configuration, version to pivot on the centre of the active grating surface   
Graph 56 Oblique Czerny Turner with different grating positions
Graph 56: Oblique Czerny-Turner spectrometer with triple grating turret, to pivot on the front surface centre of the active grating.

3.1.3.5 Dual and quadruple grating configurations are also available
3.1.3.6 Crossed beams inside the spectrometer housing
Graph 57 Crossed Ebert spectrometer
Graph 57: Crossed Ebert-Fastie.

3.1.4 The output wavelength as function of the source position.

3.1.5 The output dispersion as function of the lateral position in the field output

 Graph 58 local dispersion in the output field

Graph 58 displays four typical dispersion curves
,

3.1.6 Output dispersion and fidelity, as function of the tilt angle of the field output

 
graph 59 output shpage vs tilt angle
Graph 59 shows typical signal shapes.

3.1.7 The magnification of the transferred image in systems with non-uniform focal length or
aperture
 Graph 60 the magnification factor M

Graph 60 explains the relations between focal length (F), used width (or area W) and the reproduction size of an image. F/W is the aperture n
.

3.2.0 Multiple Stage Spectrometers


3.2.1 Basic Considerations on Double Spectrometers


3.2.1.1 Additive Setup

Graph 61 beam travel in a basic, additive, double CT
Graph 61: Basic beam travel of a classical Czerny-Turner or Ebert-Fastie double spectrometer for additive use.


3.2.1.2 Subtractive Version


Graph 62 beam travel in a basic, subtractive, double CT
Graph 62: Principal beam travel of subtractive, classical Czerny-Turner double spectrometer.


3.2.2 Modern additive double spectrometers

Triple Grating additive double Czerny Turner
Graph 63: Flexible Czerny-Turner double spectrometer with triple grating turret.

3.2.3 Subtractive double spectrometers

3.2.3.1 The classical Czerny-Turner double spectrometer with fixed coupling of gratings and additive / subtractive dispersion: 
Graph 64 beam travel in a classiceal, two way, single grating, double CT
Graph 64, shows a classical double spectrometer with fixed coupling


3.2.3.2 Subtractive double spectrometers with multiple gratings
Graph 65 beam travel in a modern, subtractive, triple grating, double CT
Graph 65: Asymmetric, subtractive double spectrometer


3.2.3.3 Mechanical Filtering in Double Spectrometers

3.2.3.4 More Configurations of flexible used Double Spectrometers
Graph 66 efficient, additive/subtractive, double CT

Graph 66 shows a front-front coupled configuration
,

3.2.4 General performance data of double spectrometers, compared to similar single stage systems
Resolution
:
Luminosity/Entendue:
Contrast:

Stability:

Working Range:

3.2.5 Triple Stage Spectrometers
 Graph 67 efficient, multiple use, triple CT
Graph 67: Triple stage spectrometer for additive, subtractive, single, double, and triple stage use


3.3.0 Prism Spectrometer
Prism spectrometer
Graph 69 shows the beam travel in a typical reflecting prism spectrometer.

Dispersion behaviour of different prism materials
Graph 70 displays the principle dispersion behaviour of four prism materials
.

3.4.0 Transmission Spectrometers

priniciple of  a  transmission spectrometer
Graph 71 displays a simplified, but realistic, transmission spectrograph.

3.5.0 Echelle Spectrometers

3.5.1 Echelle Monochromators and one-dimensional Spectrographs
Dispersion of different dispersers
Graph 72: Dispersion behaviour of different dispersers, normalized to 1 m focal length, for high resolution measurements.


3.5.2 Setup of a high resolution Echelle spectrometer to work as monochromator and single dimensional spectrograph
Scanning Echelle System
Graph 73: Flexibly applicable spectrometer for wide wavelength ranges.


3.5.3 Two-dimensional Echelle Spectrometer for the parallel Recovery of wide Wavelength Ranges at high Resolution
Interval and Overlap at 2D-CCD
GRAPH 74.
Behaviour of the spectral intervals at the CCD detector over the wavelength, and overlap.


Vertical beam deflection and spacial reserve
GRAPH 75 Vertical beam deflection by the prism und reserve of spatial resolution.

Ebert-Fastie 2D Echelle setup
Graph 76 shows a classical Ebert-Fastie spectrometer with 2D function in wide aperture and low aperture configuration.

folded Czerny-Turner 2D Echelle
Graph 77 shows a folded, symmetric 2D Echelle spectrometer.

3.5.3.1 Comparison of Ebert-Fastie and folded Czerny-Turner:
 

CCD illumination in a 2D Echelle system
Graph 78: Beam behaviour at the prism and the appearance at the detector.


3.5.3.2
Constructive Precautions.
 

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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