Optical Spectroscopy with
Basics - Building Blocks - Systems - Applications
Basics, Chapter 4: Detectors for
Monochromators and Spectrographs.
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"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.
4.02 The Detectors chapter consists of 5 parts:
1) the signals involved,
2) single element detectors,
3) data acquisition techniques,
4) diode arrays, CCDs, and other techniques,
5) definition of signal functions: response time, bandwidth, and roll-off.
Representation of Symbols
4.1.1 Work and Power of Light Signals
Graph 81: the presentation of photon energy
4.1.2 Basic Parameters of Detectors
Graph 82 displays some general signal parameters of optical detectors.
4.1.3 Detection Limit, Noise, and Signal/Noise-Ratio
Detection Limit, Noise and SNR for relative Measurements
4.2 Single Point Detectors
Graph 83: General and normalized data curves of photo tubes
Graph 84: typical Quantum Efficiencies of common Cathode materials
4.2.2 Comments on the interpretation of PMT data sheets
4.2.3 A Sample Calculation for PMT, valid for an Integration Time of 1 s
4.2.4 The Photon Counter
4.2.5 UV PMTs and Scintillators
4.3 The Illumination of Detectors, combined with Image Conversion
Graph 85: Four of many options to couple detectors and spectrometers
4.4 Channeltron and Micro-Channelplate (MCP)
Graph 86: Channeltron and Micro-Channelplate Intensifier, according to 4.4.1 und 4.4.2
4.4.2 Basis of a Micro Channelplate system is the plate itself, in the sketch marked red and with MCP.
4.5 Intensified PMT
and Single Photon Counting
4.6 Solid State Detectors
Graph 87: Some Efficiency Curves of Solid-State Detectors for the Range of 20 µm, simplified.
The General Effect of Cooling
4.6.1 Planck´s Radiation = Blackbody Radiation
Graph 88: Planck´s Radiation at low Temperatures in linear and logarithmic scale in the Range of 0.5 bis 20 µm.
4.6.2 The background charge´s magnitude of IR detectors strongly depends on the material.
The Parameter D*
connects important specifications of IR detectors in a single equation.
4.6.4 Detectors and the ambient Temperature
Graph 89: Principle of a Detector with cold aperture
Two exemplary examples shall demonstrate the Signal/Noise Ratio at IR Detectors
4.6.5 Estimation under continuous Light Situations
4.6.6 A Consideration of synchronized Measurements
Graph 90A: Simple IR spectroscopy setup for Absorption with/without Lock-In Amplifier, the Lock-In typical signals are marked violet, description follows with graph 90B.
22.214.171.124 Typical Signals at the Lock-In in optical Applications:
Graph 90B: The Lock-In Amplifier´s most important signals:
126.96.36.199 Comparison of Measurements with DC Background, clock-pulsed Background, and Lock-In-Detection
4.6.8 Estimation of the modulated Measurement
at the same Conditions as with continuous Light, described under 4.6.5
4.6.9 Tandem Detectors, also called Sandwiches
Graph 91: Principle of Sandwich Detectors.
4.6.10 Typical Parameters of Solid State Detectors, and their Interpretation
4.6.11 The Illumination of small Detector Elements
4.6.12 Charge storing Semiconductor Elements, thermal Recombination and Holding Time
4.6.13 PIN and Avalanche Diodes
4.7 Detector coupling by Fibre Optics
Graph 92: Detector coupling by fibre cable and fibre taper
4.8 Area Detectors: CCD and Array
4.8.1 Mounting of Area Detectors, and the Distribution of Wavelengths
188.8.131.52 What are the popular Kinds of Area Detectors?
4.8.2 Basic Parameters of Arrays and CCDs with and without Cooling
184.108.40.206 Pixel Size, Capacity, Sources of Noise, Dynamic Range, Shift Times, Read-out Time, ADC Conversion Time
220.127.116.11 The applicability of CCD for Spectroscopy, Image Processing, and Photography
4.8.3 Signal Transfer and Read-Out
Graph 93: Shifting processes to read-out a CCD
18.104.22.168 Combination of read-out in Imaging Mode and Display in Spectroscopy Fashion
4.8.4 CCD Architecture
Graph 94: CCD Architecture
4.8.5 CCD and Array Efficiency
22.214.171.124 Front illuminated CCD
Graph 95A: Typical Efficiency Curves of different types of Front illuminated CCD
126.96.36.199 Rear Side illuminated CCD
Graph 95B: Some typical Efficiency Curves of rear-side illuminated CCDs.
Graph 95C: Three representative InGaAs Efficiency Curves.
188.8.131.52 Interferences with Rear side illuminated CCD - Etaloning
As mentioned above, rear-side illuminated CCD show an interference, which is affected by the double pass though refractive index changes: between air or vacuum and the substrate and the substrate and the light sensitive element.
Graph 95D: typical CCD behaviour in the NIR
4.8.6 Time Control – Synchronization, Shutter, and Gating
184.108.40.206 Shutter Control
220.127.116.11 Micro Channelplate Image Intensifiers
4.8.7 Current Formats of Area Detectors
18.104.22.168 Diode Arrays
22.214.171.124 CCD Sensors
Techniques: Multi Spectra Spectroscopy, Binning and Virtual CCD Partition
126.96.36.199 Multi spectra or Multitrack Spectroscopy and vertical Binning
Graph 96: Example of the beam travel in a multi spectra experiment.
Graph 97: Read-out pattern of a square shaped CCD for Multitrack Spectroscopy
188.8.131.52 Virtual CCD Programming
4.8.9 CCD and Array Systems with Image Intensification
184.108.40.206 CCD with „On-chip Multiplication“ or „Electron Multiplication“ (EMCCD).
220.127.116.11 CCD with additional Micro channelplate image intensifier (MCP-CCD)
4.8.10 Measurements in the ms - µs Time Frame
18.104.22.168 Kinetic Measurements
Graph 98: CCD modified for Kinetic Measurements
22.214.171.124 Double Pulse Measurements
4.8.11 Extension of the spectral Efficiency into the deep UV
4.9 Other Area Detectors
4.9.1 CID and C-MOS Array
4.9.2 NIR and IR Area Detectors
4.9.2 The Positions sensitive Detectorplate (PSD)
Graph 99: Function of a PSD Detector
4.10.1 Exponential Functions and Signal Damping
Graph 100A: the general behaviour of e-functional Processes,
Graph 100B: Definition of the time constant
4.10.2 Low Pass
Graph 101: The Suppression of Signals outside the desired Bandwidth
126.96.36.199 Additional Note on the dB Interpretation.
4.10.3 Definition of Bandwidth in electric vs. opto-spectroscopic Systems.
Graph 102: Comparison of the Bandwidth Definition for System in electronic technology versus optical Spectroscopy, with Signal behaviour following a Gaussian normal distribution
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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Status April 2012