Optics of Spectroscopy Tutorial

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Optics Index

Monochromator Definitions

Table of Contents

1 Diffraction Gratings

2 Monochromators & Spectrographs

3 Spectrometer Throughput & Etendue

4 Optical Signal:Noise & Stray Light

5 Relationship Between Wavelength & Pixel Position

6 Entrance Optics

References

Product Links

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Gratings

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A TUTORIAL By J.M. Lerner and A. Thevenon

TABLE OF CONTENTS

Section 1:DIFFRACTION GRATINGS RULED & HOLOGRAPHIC

1.1 Basic Equations

1.2 Angular Dispersion

1.3 Linear Dispersion

1.4 Wavelength and Order

1.5 Resolving "Power"

1.6 Blazed Gratings

1.6.1 Littrow Condition

1.6.2 Efficiency Profiles

1.6.3 Efficiency and Order

1.7 Diffraction Grating Stray Light

1.7.1 Scattered Light

1.7.2 Ghosts

1.8 Choice of Gratings

1.8.1 When to Choose a Holographic Grating

1.8.2 When to Choose a Ruled Grating

Section 2:MONOCHROMATORS & SPECTROGRAPHS

2.1 Basic Designs

2.2 FastieEbert Configuration

2.3 CzernyTurner Configuration

2.4 CzernyTurner/FastieEbert PGS Aberrations

2.4.1 Aberration Correcting Plane Gratings

2.5 Concave Aberration Corrected Holographic Gratings

2.6 Calculating alpha and beta in a Monochromator Configuration

2.7 Monochromator System Optics

2.8 Aperture Stops and Entrance and Exit Pupils

2.9 Aperture Ratio (f/value,F.Number),and Numerical Aperture (NA)

2.9.1 f/value of a Lens System

2.9.2 f/value of a Spectrometer

2.9.3 Magnification and Flux Density

2.10 Exit Slit Width and Anamorphism

2.11 Slit Height Magnification

2.12 Bandpass and Resolution

2.12.1 Influence of the Slits

2.12.2 Influence of Diffraction

2.12.3 Influence of Aberrations

2.12.4 Determination of the FWHM of the Instrumental Profile

2.12.5 Image Width and Array Detectors

2.12.6 Discussion of the Instrumental Profile

2.13 Order and Resolution

2.14 Dispersion and Maximum Wavelength

2.15 Order and Dispersion

2.16 Choosing a Monochromator/Spectrograph

Section 3: SPECTROMETER THROUGHPUT & ETENDUE

3.1 Definitions

3.1.1 Introduction to Etendue

3.2 Relative System Throughput

3.2.1 Calculation of the Etendue

3.3 Flux Entering the Spectrometer

3.4 Example of Complete System Optimization with a Small Diameter Fiber Optic Light Source

3.5 Example of Complete System Optimization with an Extended Light Source

3.6 Variation of Throughput and Bandpass with Slit Widths

3.6.1 Continuous Spectral Source

3.6.2 Discrete Spectral Source

Section 4: OPTICAL SIGNALTONOISE RATIO AND STRAY LIGHT

4.1 Random Stray Light

4.1.1 Optical SignaltoNoise Ratio in a Spectrometer

4.1.2 The Quantification of Signal

4.1.3 The Quantification of Stray Light and S/N Ratio

4.1.4 Optimization of SignaltoNoise Ratio

4.1.5 Example of S/N Optimization

4.2 Directional Stray Light

4.2.1 Incorrect Illumination of the Spectrometer

4.2.2 Reentry Spectra

4.2.3 Grating Ghosts

4.3 S/N Ratio and Slit Dimensions

4.3.1 The Case for a SINGLE Monochromator and a CONTINUUM Light Source

4.3.2 The Case for a SINGLE Monochromator and MONOCHROMATIC Light

4.3.3 The Case for a DOUBLE Monochromator and a CONTINUUM Light Source

4.3.4 The Case for a DOUBLE Monochromator and a MONOCHROMATIC Light Source

Section 5: THE RELATIONSHIP BETWEEN WAVELENGTH AND PIXEL POSITION ON AN ARRAY

5.1 The Determination of Wavelength at a Given Location on a Focal Plane

5.1.1 Discussion of Results

5.1.2 Determination of the Position of a Known Wavelength in the Focal Plane

Section 6: ENTRANCE OPTICS

6.1 Choice of Entrance Optics

6.1.1 Review of Basic Equations

6.2 Establishing the Optical Axis of the Monochromator System

6.2.1. Materials

6.2.2 Procedure

6.3 Illuminating a Spectrometer

6.4 Entrance Optics Examples

6.4.1 Aperture Matching a Small Source

6.4.2 Aperture Matching an Extended Source

6.4.3 Demagnifying a Source

6.5 Use of Field Lenses

6.6 Pinhole Camera Effect

6.7 Spatial Filters

References

The Optics of Spectroscopy