Fourier-Transform Spectroscopy Instrumentation Engineering

by Vidi Saptari, Arthur R. Weeks

Overview

Intended for engineers and scientists who need to make hardware, software, or procedural modifications, this book explains the design and instrumentation of Michelson-interferometer-based Fourier transform spectrometers. The author defines the signal-to-noise ratio and the principles of interferometer operation, then describes the FT spectrometer's motion components, analog-to-digital conversion process, detection system, and optical components. Annotation ©2004 Book News, Inc., Portland, OR

Product Details

ISBN-13:	9780819451644
Publisher:	SPIE Press
Publication date:	11/28/2003
Series:	SPIE Press Monograph Series
Pages:	136
Product dimensions:	6.90(w) x 9.90(h) x 0.50(d)

Table of Contents

	Preface	xi
Chapter 1	Spectroscopy Instrumentation	1
1.1	Introduction	1
1.2	Types of Spectrometers	1
1.2.1	Dispersive spectrometers	1
1.2.2	Filter-based spectrometers	2
1.2.3	Fourier-transform spectrometers	3
1.3	Advantages of FT Spectrometers	4
1.3.1	Throughput or Jacquinot advantage	4
1.3.2	Multiplex or Felgett advantage	6
1.4	Discussions on FT Spectrometer Advantages	8
	References	9
Chapter 2	Signal-to-Noise Ratio	11
2.1	Signal-to-Noise Ratio Defined	11
2.2	Quantifying Signal-to-Noise Ratio	12
2.3	Practical Considerations	15
Chapter 3	Principles of Interferometer Operation	17
3.1	Overview	17
3.2	Quantitative Explanation	19
3.2.1	Light as a wave	19
3.2.2	Measurable light quantity	21
3.2.3	Interference and superposition	22
3.2.4	Polychromatic source	24
3.2.5	Fourier-transform routine	25
3.3	Theoretical Resolution	26
3.3.1	Retardation distance	26
3.3.2	Divergence angle	29
3.4	Interferogram Digital Processing	32
3.4.1	Apodization	32
3.4.2	Zero filling	34
3.4.3	Phase correction	34
	References	34
Chapter 4	Interferometer Alignment Errors	37
4.1	Error Characteristics	39
4.2	Interferogram-Modulation Error	40
4.3	Interferogram-Sampling Error	45
	References	46
Chapter 5	Motion Components and Systems	47
5.1	Actuators	48
5.1.1	Actuator types	48
5.1.2	Performance specifications for actuators	48
5.2	Driver and Amplifier	50
5.3	Bearings and Coupling Mechanism	50
5.3.1	Bearing types	51
5.3.2	Performance specifications for bearings	51
5.3.3	Discussion on bearings	53
5.4	Position Sensor	55
5.4.1	Laser interferometer	56
5.4.2	Sensor specifications	58
5.5	Homodyne Interferometer Sources of Error	59
5.5.1	Source wavelength variations	59
5.5.2	Refractive index variations	59
5.5.3	Laser detector errors	60
5.5.4	Polarization errors	60
5.5.5	Alignment errors	61
5.6	Actuator, Sensor, and Mirror Mounting	61
5.6.1	Actuator location vs. center of mass	61
5.6.2	Sensor location vs. mirror location	62
5.6.3	Sensor location vs. actuator location	62
5.7	Digital Motion Controller	63
	References	64
Chapter 6	Interferogram Data Sampling	65
6.1	Step Scan vs. Continuous Scan	66
6.2	Sampling Period	67
6.2.1	The absolute minimum: the Nyquist criteria	67
6.2.2	More than the Nyquist minimum	68
6.2.3	Anti-alias filter	69
6.3	Accuracy with Respect to OPD	71
6.3.1	Effects of sampling errors to the output spectrum	71
6.3.2	Sources of sampling error	73
6.4	Repeatable Clock Position	74
6.5	Hardware Considerations	74
	References	76
Chapter 7	Data Acquisition	77
7.1	DAQ Hardware Formats	77
7.2	Analog Inputs	77
7.2.1	Number of channels	78
7.2.2	Sampling rate	78
7.2.3	Resolution	78
7.2.4	Input ranges	78
7.2.5	Accuracy	79
7.3	Hardware Triggering and Clock Signal	79
7.4	Effects of ADC Resolution on Spectral SNR	80
Chapter 8	The Detector	83
8.1	Noise-Equivalent-Power	83
8.2	Spectral SNR quantification	84
8.3	Detector Types	87
8.4	Selection Guidelines	88
8.4.1	Spectral range and responsivity	88
8.4.2	Active area	88
8.4.3	Noise and detectivity	89
8.4.4	Linearity	89
8.4.5	Temporal bandwidth	90
8.4.6	Summary	90
	References	91
Chapter 9	Consideration of Optics and Interferometer Alignment	93
9.1	System Throughput	93
9.2	Lenses vs. Mirrors	95
9.3	Interferometer Alignment Procedure	96
Chapter 10	Signal-to-Noise Ratio Enhancement Techniques	99
10.1	Identification of Error Sources	99
10.1.1	Detector noise	99
10.1.2	Digitization noise	100
10.1.3	Interferometer alignment error	101
10.1.4	Sampling error	101
10.1.5	Light-source variation	101
10.2	Averaging	102
10.3	Temporal Modulation and Bandwidth Narrowing	103
10.4	Spectral-Bandwidth Narrowing	104
10.5	Spectral Post-Processing	105
10.6	Double Beaming	106
10.6.1	Electrical subtraction	107
10.6.2	Optical subtraction	107
10.7	Gain ranging	109
10.8	Dynamic Tilt Compensation	109
	References	110
Appendix A	Simulation of Static-Tilt Error	111
Appendix B	Sampling Circuit Example	113
Appendix C	Simulation of Sampling Error	115
	Index	117