Cavity Ring-Down Spectroscopy: Techniques and Applications	1
	Contents	7
	Preface	13
	Contributors	17
	Glossary	19
	1 An Introduction to Cavity Ring-Down Spectroscopy	23
	1.1 Introduction	23
	1.2 Direct Absorption Spectroscopy	25
	1.3 Basic Cavity Ring-Down Spectroscopy Set-Up	28
	1.4 A More Refined Picture	32
	1.5 Fitting of Cavity Ring-Down Transients	36
	1.6 A Few Examples	38
	1.7 Going Beyond the Standard Pulsed CRDS Experiment	41
	1.8 Summary	45
	References	46
	2 Cavity Enhanced Techniques Using Continuous Wave Lasers	49
	2.1 Introduction	49
	2.2 Properties of Optical Cavities and CW Lasers Relevant to Cavity Enhanced Spectroscopy	50
	2.2.1 Properties of Optical Cavities	50
	2.2.2 Laser Bandwidth, Noise, and Cavity Interactions	54
	2.3 Experimental Methods for CW Laser Cavity Enhanced Spectroscopy	56
	2.3.1 CW-Cavity Ring-Down Spectroscopy (CW-CRDS)	56
	2.3.2 Cavity Enhanced Absorption Spectroscopy (CEAS/ICOS)	61
	2.3.3 Phase Shift Cavity Ring-Down Spectroscopy (PSCRDS)	64
	2.4 Spectroscopy with Resonant Cavities	69
	2.4.1 Frequency Locked CW-CRDS	69
	2.4.2 Methods for Locking Cavities and Lasers	70
	2.4.3 Optical Feedback CRDS and CEAS (OF-CRDS/OF-CEAS)	72
	2.4.4 Other Locked-Cavity Techniques	75
	2.4.5 Optical Heterodyne Cavity Ring-Down Spectroscopy	76
	2.5 Summary	76
	References	77
	3 Broadband Cavity Ring-Down Spectroscopy	79
	3.1 Introduction	79
	3.2 The Time and Wavelength Evolution of a Single Ring-Down Event	80
	3.3 Two-Dimensional Techniques: Resolving Broadband Cavity Output in Time and Wavelength	83
	3.4 One-Dimensional Techniques: Time or Wavelength	86
	3.4.1 Wavelength Selection Methods	86
	3.4.2 Fourier Transform Methods	87
	3.4.3 Phase Shift Cavity Methods	88
	3.4.4 Broadband Cavity Enhanced Absorption Spectroscopy	90
	3.5 How to Extract Quantitative Information from Broadband Spectra	92
	3.5.1 Mirror Reflectivity Considerations	92
	3.5.2 Differential Optical Absorption Spectroscopy	93
	3.5.3 Multi-Exponential Decays	96
	3.6 Optimising the Sensitivity of a Broadband Measurement	101
	3.7 Applications of Broadband Cavity Methods	105
	3.7.1 Atmospheric Measurements	105
	3.7.2 Liquid Phase Spectroscopy	107
	References	109
	4 Cavity Ring-Down Spectroscopy in Analytical Chemistry	111
	4.1 Introduction	111
	4.1.1 Absorbance Detection in Liquid Flow Systems	111
	4.1.2 Requirements for Detection Cells for Analytical Purposes	113
	4.2 Condensed Media CRDS	114
	4.2.1 Studying Solid-Phase Samples with CRDS	114
	4.2.2 Studying Liquid-Phase Samples With CRDS	115
	4.2.3 Incoherent Broad-Band Cavity-Enhanced Absorption Spectroscopy: IBBCEAS	118
	4.2.4 CRDS Absorption Detection in Liquid Chromatography	119
	4.3 Evanescent-Wave CRDS	124
	4.3.1 EW-CRDS Using Monolithic Resonators	124
	4.3.2 Applications of EW-CRDS to Condensed Media	126
	4.4 Future Trends and Perspectives	129
	References	130
	5 Cavity Ring-Down Spectroscopy Using Waveguides	135
	5.1 Introduction	135
	5.2 The Basic Experiments	136
	5.2.1 The Fiber-Loop Ring-Down Experiment	136
	5.2.2 The FBG Cavity Ring-Down Experiment	138
	5.3 Optics and Instrumentation	139
	5.3.1 Waveguide Optics	139
	5.3.2 Waveguide Materials	143
	5.3.3 Fiber-Optic Components	146
	5.4 Review of Waveguide CRD Literature	149
	5.4.1 Measurement of Optical Loss of Connectors and Fibers	149
	5.4.2 Mechanical Sensing with Waveguide CRD	149
	5.4.3 Interfaces to Microfluidic Devices	154
	5.4.4 Lensed Fiber Ends	154
	5.4.5 Amplified Fiber CRD	156
	5.4.6 Evanescent Field Absorption Spectroscopy Using Waveguide CRD	158
	5.4.7 Choice of Wavelength for Absorption Detection	159
	5.4.8 Refractive Index Sensing Using LPGs in Fiber Cavities	160
	5.5 Conclusion and Outlook	162
	Acknowledgements	162
	References	163
	6 Cavity Ring-Down Spectroscopy of Molecular Transients of Astrophysical Interest	167
	6.1 Introduction	167
	6.1.1 Astrochemical Setting	167
	6.1.2 Plasma Techniques: Cell Discharges and Plasma Expansions	169
	6.1.3 Sensitive and Selective Detection Schemes	170
	6.2 Experimental	171
	6.2.1 High-Pressure Pulsed Planar Plasma Source	171
	6.2.2 Pulsed Cavity Ring Down Spectroscopy – the Detection Scheme	173
	6.2.3 Pulsed Cavity Ring-Down Spectroscopy – an Example	173
	6.2.4 CW Cavity Ring-Down Spectroscopy – the Detection Scheme	177
	6.2.5 CW Cavity Ring-Down Spectroscopy – an Example	178
	6.2.6 Frequency Plasma Double Modulation Spectroscopy – the Detection Scheme	179
	6.2.7 Frequency Plasma Double Modulation Spectroscopy – an Example	181
	6.2.8 CW Electron Impact Source	182
	6.2.9 Production Modulation Spectroscopy – Detection Scheme and Example	184
	6.2.10 CW Cavity Ring Down Spectroscopy – Detection Scheme and Example	186
	6.3 Astronomical Considerations	189
	6.4 Results	190
	6.5 Outlook	194
	Acknowledgements	195
	References	195
	7 Applications of Cavity Ring-Down Spectroscopy in Atmospheric Chemistry	203
	7.1 Brief Overview	203
	7.2 Measurement of Trace Atmospheric Species by CRDS	206
	7.2.1 An Example of a CRDS Apparatus for Atmospheric Composition Measurements	207
	7.2.2 Open-Path CRDS Measurements of Atmospheric Composition	210
	7.2.3 Diode Laser CRDS Detection of Atmospheric VOCs and Preconcentration of Air Samples	212
	7.2.4 Considerations for the Sensitivity of Atmospheric CRDS Instruments	214
	7.3 Laboratory-Based Studies of Atmospheric Interest	215
	7.3.1 Rate Constants	215
	7.3.2 Quantum Yields	219
	7.3.3 Absorption Cross-Sections	221
	7.4 Optical Properties of Atmospheric Aerosol Particles	223
	7.4.1 Light Scattering by Atmospheric Aerosol Particles	224
	7.4.2 Effect of Aerosols on Radiative Forcing of the Atmosphere and Climate Change	224
	7.4.3 Some Fundamental Principles of CRDS of Aerosols	227
	7.5 Future Developments	229
	References	230
	8 Cavity Ring-Down Spectroscopy for Medical Applications	235
	8.1 Introduction	235
	8.2 Trace Gases in Medicine and Biology	236
	8.2.1 Composition of Exhaled Human Breath	236
	8.2.2 Other Biological Sources of Volatile Markers	239
	8.3 Instrumentation for Laser Analytics of Breath and Other Biological Gas Samples	240
	8.3.1 Sample Collection and Preparation	240
	8.3.2 Laser Spectroscopic Approach	242
	8.3.3 Comparison with Conventional Techniques	245
	8.4 Applications to Life Sciences	245
	8.4.1 Monitoring Exhaled Ethane	245
	8.4.2 Monitoring Exhaled CO	250
	8.4.3 Analysis of Blood NO	251
	8.5 Conclusion and Perspectives	254
	Acknowledgements	255
	References	255
	9 Studies into the Growth Mechanism of a-Si:H Using in-situ Cavity Ring-Down Techniques	259
	9.1 Introduction	259
	9.2 Gas Phase CRDS on SiHx Radicals	262
	9.2.1 Production and Loss Processes of Radicals Under Plasma Conditions	262
	9.2.2 Experimental Set-Up for Plasma Deposition of a-Si:H and CRDS Measurements	264
	9.2.3 Cavity Ring-Down Measurements During ETP Deposition of a-Si:H	268
	9.3 Thin Film CRDS on Dangling Bonds in a-Si:H Films (ex situ)	274
	9.3.1 General Considerations	276
	9.3.2 Measuring ex-situ Dangling Bonds in a-Si:H Films	282
	9.4 Evanescent Wave CRDS on Dangling Bonds During a-Si:H Film Growth	285
	9.4.1 The Evanescent Wave CRDS Set-Up	286
	9.4.2 Measuring Dangling Bonds During a-Si:H Film Growth	287
	Acknowledgements	290
	References	291
	10 Cavity Ring-Down Spectroscopy for Combustion Studies	295
	10.1 Introduction	295
	10.2 General Description of Cavity Ring-Down Spectroscopy in Flames	299
	10.3 Experimental Set-Up	302
	10.3.1 Burners and Flames	302
	10.3.2 Laser Sources	304
	10.3.3 Ring-Down Cavity for Low Pressure Flames	305
	10.3.4 Typical Designs of Cavities for Flame Experiments	305
	10.3.5 Mode Matching under Flame Conditions	306
	10.3.6 Cavity Alignment	308
	10.3.7 Detection Scheme	310
	10.4 Quantitative Concentration Measurements by CRD Spectroscopy in Flames	311
	10.4.1 Concentration Determination for Diatomic Species	312
	10.4.2 Precautions	312
	10.4.3 Absolute Concentration Measurements for an Ideal Case	313
	10.4.4 A Numerical Example: CH Absorption	316
	10.5 Concentration Profile Determination	317
	10.5.1 General Method	317
	10.5.2 Case of a Nonhomogeneous Concentration Field	318
	10.6 Specific Difficulties in Combustion Studies	322
	10.6.1 CRD Measurements Under Strong Absorption Conditions	322
	10.6.2 Temperature and Thermal Gradient Effects	324
	10.6.3 Stable Species	324
	10.7 Case of Particles: Soot Volume Fraction Determination	325
	10.8 Conclusion and Prospects	329
	Acknowledgements	329
	References	329
	Index	335
	Colour Plate	345