1 Introduction ................................................. 1
2 Absorption and Emission of Light ............................. 5
2.1 Cavity Modes ............................................ 5
2.2 Thermal Radiation and Planck's Law ...................... 9
2.3 Absorption, Induced, and Spontaneous Emission .......... 11
2.4 Basic Photometric Quantities ........................... 15
2.4.1 Definitions ..................................... 16
2.4.2 Illumination of Extended Areas .................. 18
2.5 Polarization of Light .................................. 20
2.6 Absorption and Emission Spectra ........................ 22
2.7 Transition Probabilities ............................... 26
2.7.1 Lifetimes, Spontaneous and Radiationless
Transitions ..................................... 27
2.7.2 Semiclassical Description: Basic Equations ...... 29
2.7.3 Weak-Field Approximation ........................ 32
2.7.4 Transition Probabilities with Broad-Band
Excitation ...................................... 34
2.7.5 Phenomenological Inclusion of Decay Phenomena ... 35
2.7.6 Interaction with Strong Fields .................. 37
2.7.7 Relations Between Transition Probabilities,
Absorption Coefficient, and Line Strength ....... 41
2.8 Coherence Properties of Radiation Fields ............... 42
2.8.1 Temporal Coherence .............................. 43
2.8.2 Spatial Coherence ............................... 44
2.8.3 Coherence Volume ................................ 46
2.8.4 The Coherence Function and the Degree
of Coherence .................................... 49
2.9 Coherence of Atomic Systems ............................ 54
2.9.1 Density Matrix .................................. 54
2.9.2 Coherent Excitation ............................. 56
2.9.3 Relaxation of Coherently Excited Systems ........ 58
Problems ............................................... 58
3 Widths and Profiles of Spectral Lines ....................... 61
3.1 Natural Linewidth ...................................... 62
3.1.1 Lorentzian Line Profile of the Emitted
Radiation ....................................... 62
3.1.2 Relation Between Linewidth and Lifetime ......... 64
3.1.3 Natural Linewidth of Absorbing Transitions ...... 66
3.2 Doppler Width .......................................... 70
3.3 Collisional Broadening of Spectral Lines ............... 75
3.3.1 Phenomenological Description .................... 75
3.3.2 Relations Between Interaction Potential,
Line Broadening, and Shifts ..................... 80
3.3.3 Collisional Narrowing of Lines .................. 84
3.4 Transit-Time Broadening ................................ 84
3.5 Homogeneous and Inhomogeneous Line Broadening .......... 88
3.6 Saturation and Power Broadening ........................ 90
3.6.1 Saturation of Level Population by Optical
Pumping ......................................... 90
3.6.2 Saturation Broadening of Homogeneous Line
Profiles ........................................ 92
3.6.3 Power Broadening ................................ 93
3.7 Spectral Line Profiles in Liquids and Solids ........... 95
Problems ............................................... 97
4 Spectroscopic Instrumentation ............................... 99
4.1 Spectrographs and Monochromators ....................... 99
4.1.1 Basic Properties ............................... 101
4.1.2 Prism Spectrometer ............................. 1ll
4.1.3 Grating Spectrometer ........................... 115
4.2 Interferometers ....................................... 124
4.2.1 Basic Concepts ................................. 124
4.2.2 Michelson Interferometer ....................... 125
4.2.3 Fourier Spectroscopy ........................... 129
4.2.4 Mach-Zehnder Interferometer .................... 131
4.2.5 Sagnac Interferometer .......................... 134
4.2.6 Multiple-Beam Interference ..................... 136
4.2.7 Plane Fabry-Perot Interferometer ............... 144
4.2.8 Confocal Fabry-Perot Interferometer ............ 152
4.2.9 Multilayer Dielectric Coatings ................. 157
4.2.10 Interference Filters ........................... 162
4.2.11 Birefringent Interferometer .................... 165
4.2.12 Tunable Interferometers ........................ 169
4.3 Comparison Between Spectrometers and
Interferometers ....................................... 170
4.3.1 Spectral Resolving Power ....................... 170
4.3.2 Light-Gathering Power .......................... 173
4.4 Accurate Wavelength Measurements ...................... 174
4.4.1 Precision and Accuracy of Wavelength
Measurements ................................... 175
4.4.2 Today's Wavemeters ............................. 178
4.5 Detection of Light .................................... 188
4.5.1 Thermal Detectors .............................. 191
4.5.2 Photodiodes .................................... 198
4.5.3 Photodiode Arrays .............................. 208
4.5.4 Charge-Coupled Devices (CCDs) .................. 210
4.5.5 Photoemissive Detectors ........................ 212
4.5.6 Detection Techniques and Electronic
Equipment ...................................... 224
4.6 Conclusions ........................................... 231
Problems .............................................. 231
5 Lasers as Spectroscopic Light Sources ...................... 235
5.1 Fundamentals of Lasers ................................ 235
5.1.1 Basic Elements of a Laser ...................... 235
5.1.2 Threshold Condition ............................ 236
5.1.3 Rate Equations ................................. 238
5.2 Laser Resonators ...................................... 241
5.2.1 Open Optical Resonators ........................ 242
5.2.2 Spatial Field Distributions in Open
Resonators ..................................... 245
5.2.3 Confocal Resonators ............................ 247
5.2.4 General Spherical Resonators ................... 250
5.2.5 Diffraction Losses of Open Resonators .......... 251
5.2.6 Stable and Unstable Resonators ................. 253
5.2.7 Ring Resonators ................................ 258
5.2.8 Frequency Spectrum of Passive Resonators ....... 260
5.3 Spectral Characteristics of Laser Emission ............ 262
5.3.1 Active Resonators and Laser Modes .............. 263
5.3.2 Gain Saturation ................................ 266
5.3.3 Spatial Hole Burning ........................... 268
5.3.4 Multimode Lasers and Gain Competition .......... 269
5.3.5 Mode Pulling ................................... 273
5.4 Experimental Realization of Single-Mode Lasers ........ 274
5.4.1 Line Selection ................................. 275
5.4.2 Suppression of Transverse Modes ................ 279
5.4.3 Selection of Single Longitudinal Modes ......... 281
5.4.4 Intensity Stabilization ........................ 288
5.4.5 Wavelength Stabilization ....................... 291
5.5 Controlled Wavelength Tuning of Single-Mode Lasers .... 302
5.5.1 Continuous Tuning Techniques ................... 303
5.5.2 Wavelength Calibration ......................... 308
5.5.3 Frequency Offset Locking ....................... 310
5.6 Linewidths of Single-Mode Lasers ...................... 310
5.7 Tunable Lasers ........................................ 314
5.7.1 Basic Concepts ................................. 314
5.7.2 Semiconductor-Diode Lasers ..................... 315
5.7.3 Tunable Solid-State Lasers ..................... 321
5.7.4 Color-Center Lasers ............................ 325
5.7.5 Dye Lasers ..................................... 329
5.7.6 Excimer Lasers ................................. 346
5.7.7 Free-Electron Lasers ........................... 349
5.8 Nonlinear Optical Mixing Techniques ................... 352
5.8.1 Physical Background ............................ 353
5.8.2 Phase Matching ................................. 358
5.8.3 Second-Harmonic Generation ..................... 360
5.8.4 Quasi Phase Matching ........................... 366
5.8.5 Sum-Frequency and Higher-Harmonic Generation ... 368
5.8.6 X-Ray Lasers ................................... 373
5.8.7 Difference-Frequency Spectrometer .............. 377
5.8.8 Optical Parametric Oscillator .................. 380
5.8.9 Tunable Raman Lasers ........................... 384
5.9 Gaussian Beams ........................................ 388
Problems ................................................... 394
Solutions ..................................................... 397
References .................................................... 425
Subject Index ................................................. 453
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