Synchrotron Radiation Research

1. An Overview of Synchrotron Radiation Research.- 1. Introduction.- 2. An Interdisciplinary Tool.- 3. Some Recent History.- 4. Earlier History.- 5. Photon Physics.- 6. The Future.- References.- 2. Properties of Synchrotron Radiation.- 1. Introduction.- 2. Radiated Power.- 3. Spectral and Angular Distribution.- 4. Polarization.- 5. Pulsed Time Structure.- 6. Brightness and Emittance.- References.- 3. Synchrotron Radiation Sources, Research Facilities, and Instrumentation.- 1. Introduction.- 2. Sources of Synchrotron Radiation.- 2.1. General.- 2.2. Storage Rings.- 2.3. Synchrotrons.- 3. Synchrotron Radiation Research Facilities.- 3.1. General.- 3.2. Beam Channels.- 3.2.1. Vacuum Considerations.- 3.2.2. Thermal Problems.- 3.2.3. Beryllium Windows.- 3.3. Radiation Shielding and Personnel Protection Interlock Systems.- 3.3.1. General.- 3.3.2. Low-Energy Storage Rings.- 3.3.3. High-Energy Storage Rings.- 3.4. Synchrotron Radiation Beam Position Monitoring and Control.- 3.5. Experimental Support Facilities.- 4. Instrumentation for Synchrotron Radiation Research.- 4.1. General.- 4.2. Mirrors.- 4.3. Monochromators.- 4.4. Detectors.- References.- 4. Inner-Shell Threshold Spectra.- 1. Introduction.- 1.1. Kossel-Kronig Structure.- 1.2. Lifetime Effects.- 1.3. Early Work on Excitons.- 1.4. Atomic Effects.- 2. Experimental Techniques.- 2.1. Use of Synchrotron Radiation.- 2.2. Synchrotron Radiation Monochromators.- 2.3. Various Spectroscopic Techniques.- 2.4. Absorption Measurements on Solids and Gases.- 3. Hydrogenlike Photoabsorption Spectra.- 3.1. The Hydrogen Model for X-Ray Absorption; K Edge of Argon.- 3.2. K Edge of Chlorine in Cl2 Gas.- 4. Oscillator Strength for Rydberg and Continuum Transitions.- 4.1. Atomic Absorption in the Dipole Approximation.- 4.2. Oscillator Strength and Spectral Density.- 4.3. Comparison of Hydrogen and Lithium Valence Transitions.- 4.4. K Edge of Neon Gas.- 5. Core Excitons in Insulators.- 5.1. Valence Excitons in Solid Neon.- 5.2. L Edge of Solid Argon; Altarelli-Bassani Theory.- 5.3. N2, 3 Edge of Rubidium in RbCl; Satoko-Sugano Theory.- 5.4. Deeper Core Structure in RbCl.- 5.5. Recent Reflectivity Data on the Potassium Halides.- 5.6. K Edge of Lithium in the Lithium Halides; Zunger-Freeman Theory.- 6. Threshold Resonances in Solids.- 6.1. White Lines, the K Edge of Germanium, and the L Edge of Tantalum.- 6.2. K Edge of Arsenic; Recent Theory.- 6.3. L Edge of Silicon and the Elliot Exciton.- 6.4. K Edge of Titanium in Some Transition-Metal Compounds, TiSe2 and MnO2.- 7. Simple Polyatomic Gases.- 7.1. Inner-Outer Well Potential.- 7.2. K Edge of Nitrogen in N2 Gas.- 7.3. K Edge of Carbon in Methane and the Fluoromethanes.- 7.4. Second-Row Hydrides and Fluorides; Effect of Condensation on the SiH4 and SiF4 Spectra.- 7.5. K Edge of Germanium in GeCl4, GeBr4, and GeH4.- 7.6. Summary Remarks.- References.- 5. Electron Spectrometry of Atoms and Molecules.- 1. Introduction.- 2. The Domain of Synchrotron Radiation.- 3. Basic Relations and Background.- 3.1. Energies.- 3.2. Photoionization Cross Sections.- 3.3. Angular Distribution of Photoelectrons.- 3.4. Two-Electron Processes.- 3.5. Level Widths.- 4. Experimental Apparatus and Procedures.- 4.1. The Monochromator.- 4.2. The Electron Spectrometer.- 4.2.1. Energy Calibration.- 4.2.2. Spectrometer Function.- 4.2.3. Transmission Function and Intensity Measurements.- 4.3. Source for Circularly Polarized Light.- 4.4. Comparison with Discrete Sources.- 5. Restricted Photoelectron Spectrometry-Energies.- 6. Level Widths and Line Widths.- 7. Partial Photoionization Cross Sections.- 7.1. Atoms.- 7.1.1. Spin-Orbit Photoelectron Intensity Ratios.- 7.1.2. Two-Electron Transitions.- 7.2. Threshold Laws.- 7.3. Quasi-Atomic Systems.- 7.4. Molecules.- 8. Angular Distributions of Photoelectrons.- 8.1. Closed-Shell Atoms.- 8.2. Open-Shell Atoms.- 8.3. Molecules.- 9. Resonances and Autoionization.- 9.1. Atoms.- 9.2. Molecules.- 10. Post-Collision Interactions.- 11. Photoexcited Auger Spectra.- 12. Coincidence Experiments.- 13. Outlook.- References.- 6. Photoemission as a Tool to Study Solids and Surfaces.- 1. General Considerations.- 1.1. The Physics of the Photoemission Process.- 1.2. The Characteristics of Synchrotron Radiation Important for Photoemission Studies.- 1.3. The Probing Depth in Photoemission.- 1.4. The Energy Dependence of Partial Photoionization Cross Sections.- 1.5. Different Photoemission Techniques.- 2. Experimental Details.- 2.1. Synchrotron Radiation Beam Lines.- 2.2. Monochromators.- 2.3. Sample Chambers, Energy Analyzers, and Detector Systems.- 2.4. Concluding Remarks.- 3. Research Applications.- 3.1. Introduction.- 3.2. Bulk Electronic Structure.- 3.2.1. The Bulk Electronic Structure of the Ge Valence Band.- 3.2.2. The Density of States of Some IV, III-V, II-VI, and I-VII Compounds: A Comparison between Theory and Experiment.- 3.2.3. The Electronic Structure of the Gold Valence Band.- 3.3. Surface Electronic Structure.- 3.3.1. Surface States and Resonances on Single Crystals of Metals.- 3.3.2. The Surface Electron Structure of GaAs (110).- 3.4. Chemisorption and Oxidation Studies.- 3.4.1. Oxygen Chemisorption and the Initial Oxidation Stages on the GaAs (110) Surface.- 3.4.2. Chemisorption of CO on Transition Metal Surfaces-Molecular Levels.- 3.4.3. The Effect of Chemisorption on the Substrate Core Levels.- 3.4.4. The Chemisorption and Oxidation Properties of Al Surfaces.- 3.5. The Electronic Structure of Interfaces.- 3.5.1. Oxygen Chemisorption onto Si (111) and the Si-SiO2 Interface.- 3.5.2. Metal Overlayers on III-V Semiconductor Surfaces.- 3.5.3. Cesium-Oxygen Overlayers on GaAs (110).- 3.6. The Electronic Structure of Cu-Ni Alloy Surfaces.- 3.7. Concluding Remarks.- 4. Future Prospects and Developments.- References.- 7. Microlithography with Soft X Rays.- 1. Introduction.- 2. X-Ray Replication and Results.- 3. Fundamentals.- 3.1. X-Ray Sources.- 3.1.1. Synchrotron Radiation.- 3.1.2. Electron Bombardment X-Ray Sources.- 3.2. Optics.- 3.3. Absorption.- 3.4. Photoelectrons.- 3.5. Energy Deposition.- 3.6. Energy Deposition Effects.- 4. X-Ray Lithography Technology.- 4.1. X-Ray Sources.- 4.1.1. Novel X-Ray Sources.- 4.1.2. Electron Bombardment Sources.- 4.1.3. Synchrotron Radiation Sources.- 4.2. Windows and Masks.- 4.3. Resists.- 4.4. Alignment and Distortion.- 4.5. Radiation Damage to Devices.- 5. System Approaches.- References.- 8. Soft X-Ray Microscopy of Biological Specimens.- 1. Introduction.- 2. Contrast Mechanisms.- 2.1. Removal of Photons; Transmission X-Ray Microscopy.- 2.2. Reaction Products; Fluorescence X-Ray Microscopy and Electron-Emission X-Ray Microscopy.- 2.3. Damage to the Absorbing Material.- 2.4. Quantitative Relationships.- 2.5. Summary.- 3. Image Formation.- 3.1. Magnification by Electron Optics.- 3.1.1. Contact Microradiography: General.- 3.1.2. Contact Microradiography: Resolution and Sensitivity of Resists.- 3.1.3. Contact Microradiography: Resolution of the Technique.- 3.1.4. Contact Microradiography: Details of the Technique.- 3.1.5. Contact Microradiography with Direct Photon-Electron Conversion.- 3.1.6. Image Formation Using Electrons Emitted from the Specimen.- 3.2. Magnification by X-Ray Optics.- 3.2.1. Grazing-Incidence Mirrors.- 3.2.2. Point Projection Microscopy.- 3.2.3. Microscopy with Zone Plate Objectives.- 3.2.4. Holographic Microscopy.- 3.3. Scanning Microscopy.- 3.3.1. The Microscope of Horowitz and Howell.- 3.3.2. Future Prospects for Scanning Microscopy.- 3.4. Summary.- 4. Sources of Soft X Rays for Microscopy.- 4.1. Requirements.- 4.2. Soft X-Ray Sources.- 4.2.1. Synchrotron Radiation.- 4.2.2. Conventional X-Ray Generators.- 4.2.3. Plasma Sources.- 5. Mapping the Concentration of a Particular Atomic Species.- 5.1. Absorption Microanalysis.- 5.2. Fluorescence Microanalysis.- 5.3. Summary.- 6. Additional Technical Aspects.- 6.1. Wet Specimens.- 6.2. Readout of Resist Images by Transmission Electron Microscopy.- 6.3. 3-D Imaging.- 7. Summary and Conclusions.- References.- 9. Synchrotron Radiation as a Modulated Source for Fluorescence Lifetime Measurements and for Time-Resolved Spectroscopy.- 1. Introduction: Source Properties.- 2. Time Modulation of Synchrotron Radiation Sources.- 2.1. Storage Rings.- 2.2. Synchrotrons.- 2.3. Electron Bunches and Their Behavior in a Storage Ring.- 2.4. Optical Properties of the Pulsed Source.- 2.5. Source Parameters.- 2.6. Comparison with Other Sources.- 3. Experimental Techniques for Time-Resolved Measurements.- 3.1. Direct Time Measurements.- 3.2. Single-Photon Counting Method.- 3.3. Phase-Shift Measurements.- 3.4. Time-Resolved Spectroscopy.- 4. Research Applications.- 4.1. Fluorescence Lifetime Measurements of Organic Molecules.- 4.2. Time-Resolved Spectroscopy of Rare Gases.- 4.2.1. Pure Rare-Gas Solids.- 4.2.2. Solid Rare-Gas Mixtures.- 4.2.3. Rare-Gas Measurements.- 4.3. Time-Resolved Fluorescence Spectroscopy of Large Molecules.- References.- 10. The Principles of X-Ray Absorption Spectroscopy.- 1. Introduction-Overview of X-Ray Absorption Spectroscopy and exafs Applications.- 2. Physics of Photoabsorption in Atoms.- 2.1. Fully Relaxed Transitions.- 2.2. Shake Up and Shake Off.- 2.3. Form of the One-Electron Cross Section.- 2.4. Effect of Core-Hole Lifetime.- 3. Photoabsorption in Molecular and Condensed Systems.- 3.1. General Features of the Spectrum.- 3.2. Photoabsorption in the exafs Region.- 3.3. The Thermal Average of the exafs Cross Section.- 3.4. Determination of Electron-Atom Scattering Phase Shifts and Amplitudes in the exafs Region.- 3.5. Many-Electron Effects in the exafs Spectrum.- 3.5.1. Inelastic Events.- 3.5.2. Effect of Screening in Metals.- 3.5.3. Exchange and Correlation Effects on the One-Electron Potential.- 3.6. The Near-Edge Region of the X-Ray Absorption Spectrum-Multiple Scattering Effects.- 4. Instrumentation for X-Ray Absorption Spectroscopy.- 4.1. Introduction.- 4.2. X-Ray Monochromators.- 4.3. X-Ray Detectors.- 4.3.1. Ionization Chambers.- 4.3.2. Proportional Counters.- 4.3.3. Scintillation Counters.- 4.3.4. Semiconductor Devices.- 4.3.5. Analyzing Detectors.- 5. Numerical Analysis of X-Ray Absorption Data-Extraction of Physical Parameters.- 5.1. General Considerations in the Analysis of exafs Data.- 5.2. Subtracting the Background-Setting the k Scale.- 5.3. Fourier Filtering.- 5.4. Nonlinear Curve Fitting of exafs Data-Application to Model Compounds and Multishell Parameter Determination.- 5.5. Numerical Analysis of X-Ray Absorption Edge Data.- References.- 11. Extended X-Ray Absorption Fine Structure in Condensed Materials.- 1. Introduction.- 2. Periodic and Quasi-Periodic Solids.- 3. Surface exafs.- 4. Disordered Solids.- 5. Liquids.- 6. X-Ray Sources.- 7. Future Directions.- References.- 12. X-Ray Absorption Spectroscopy: Catalyst Applications.- 1. Introduction.- 2. Nature of Catalysts.- 3. Analysis of exafs Data.- 4. Experimental Procedures.- 5. Structure of Catalysts.- 5.1. Dispersed Metal Catalysts.- 5.2. Metal Oxide Catalysts.- 5.3. Homogeneous Catalysts.- 6. Near-Edge Structure.- 7. Status and Outlook.- References.- 13. X-Ray Absorption Spectroscopy of Biological Molecules.- 1. Introduction.- 2. Discussion of Experimental Techniques Appropriate to Biological Molecules.- 2.1. Transmission versus Fluorescence.- 2.2. Fluorescence Detectors with Energy Discrimination.- 3. exafs Data Analysis for Biological Molecules.- 3.1. Scatterer Identification.- 3.2. Amplitudes and Numbers of Scatterers.- 3.3. An Example of Structure Determination.- 4. Selected exafs Applications to Problems of Biological Significance.- 4.1. Rubredoxin.- 4.2. Hemoglobin.- 4.3. Nitrogenase.- 4.4. Cytochrome P-450 and Chloroperoxidase.- 4.5. The "Blue" Copper Proteins.- 4.6. Xanthine Oxidase and Sulfite Oxidase.- 4.7. Hemocyanin.- 4.8. Ferritin.- 4.9. Cytochrome Oxidase.- 4.10. Calcium Binding Proteins.- 5. X-Ray Absorption Edge Structure for Biological Molecules.- 5.1. The Effect of Oxidation State on Edge Position.- 5.2. Continuum Spectral Features.- 5.3. Applications to Specific Biological Molecules.- 6. Prospects.- References.- 14. X-Ray Fluorescence Microprobe for Chemical Analysis.- 1. Introduction.- 2. Quantitative Analysis and Fluorescence Cross Sections.- 2.1. Equations for Quantitative X-Ray Fluorescence Analysis.- 2.2. Minimum Detectable Limit.- 2.3. Comparison of X-Ray and Charged-Particle Fluorescence Cross Sections.- 2.4. Backgrounds Beneath the Fluorescence Signals.- 2.5. Energy Deposited Versus Fluorescence Production.- 2.6. Summary of the Properties of X Rays and Charged Particles for Fluorescence Excitation.- 2.7. Microprobe Spatial Resolutions; Charged-Particle Intensities.- 3. Results of X-Ray Fluorescence Measurements with Synchrotron Radiation.- 3.1. Fluorescence Excitation with the Continuum Radiation.- 3.2. Fluorescence Excitation with Monochromatic Radiation.- 3.2.1. Experimental Arrangement.- 3.2.2. Fluorescence Spectra and Detectable Limits.- 3.2.3. Minimum Detection Limits for 37-keV Radiation.- 3.2.4. Intrinsic Background for X-Ray-Excited Fluorescence: Summary of Signal-to-Background Ratios.- 4. Optics for an X-Ray Microprobe.- 4.1. Mirrors for Focusing the Continuum Spectrum.- 4.2. Mirrors and Crystals for Focusing Monoenergetic X Rays.- 5. Final Comparative Analysis and Conclusions.- References.- 15. Small-Angle X-Ray Scattering of Macromolecules in Solution.- 1. Introduction.- 2. The Small-Angle Scattering Intensity.- 2.1. The Probability of Small-Angle Scattering from a Dilute Solution.- 2.2. The Energy Spectrum of the Source.- 2.3. The Efficiency of Gas-Filled Chambers.- 3. Small Angle Scattering Instruments.- 3.1. Instruments with One Monochromator Crystal.- 3.2. The Mirror-Monochromator System.- 3.3. The Double-Monochromator System.- 3.4. The Energy Dispersive Method.- 4. Experimental Results.- 5. Conclusions.- References.- 16. Small-Angle Diffraction of X Rays and the Study of Biological Structures.- 1. Design Criteria for Small-Angle Diffraction.- 1.1. Conditions Imposed by the Specimen and Experiment.- 1.1.1. Specimens.- 1.1.2. Experimental Requirements.- 1.2. X-Ray Optics and Optimalization.- 1.2.1. Definitions.- 1.2.2. Optical Principles of Curved Mirrors and Curved Crystal Monochromators.- 1.2.3. Optical Phase Space.- 1.2.4. The Optimum Condition.- 1.2.5. Choice of Wavelength.- 1.3. Small-Angle Diffraction Cameras for Synchrotron Radiation.- 1.3.1. Remote Control.- 1.3.2. Vacuum Window.- 1.3.3. Curved Mirrors.- 1.3.4. Curved Crystal Monochromators.- 1.3.5. Mirror-Monochromator Camera at desy.- 1.3.6. Mirror-Monochromator Camera at nina.- 1.3.7. Mirror-Monochromator Camera at spear.- 1.3.8. Monochromator-Mirror Camera at vepp-3.- 1.3.9. Mirror-Monochromator Cameras at doris.- 1.3.10. The Separated Function Focusing Monochromator at spear.- 1.4. Conditions Imposed by Detector Technology.- 1.5. A Comparison of the Theoretical and Actual Performance of Mirror-Monochromator Systems.- 2. Applications.- 2.1. Muscle Fibers; Real Time Experiments on Muscle.- 2.1.1. Frog Muscle.- 2.1.2. Insect Flight Muscle.- 2.2. Collagen.- 2.3. DNA Fibers.- 3. Extensions of the Methodology.- 3.1. Wide-Band Monochromators-A Technological Challenge.- 3.2. Towards an Optimum Design.- References.- 17. Single-Crystal X-Ray Diffraction and Anomalous Scattering Using Synchrotron Radiation.- 1. Introduction.- 1.1. Uses of Synchrotron Radiation in Macromolecular Crystallography.- 1.1.1. High Intensity.- 1.1.2. The Phase Problem.- 1.1.3. Large Unit Cells.- 1.2. Early Protein Crystallography Results at spear.- 1.3. Crystallography at Other Synchrotron Radiation Laboratories.- 1.4. Scope of the Remainder of the Chapter.- 2. A Four-Circle Diffractometer Used with Synchrotron Radiation.- 2.1. Introduction.- 2.2. Description of the System.- 2.2.1. Focusing Mirror-Monochromator System.- 2.2.2. Diffractometer Modifications.- 2.2.3. Alignment Carriage.- 2.2.4. Transportable Radiation Hutch.- 2.2.5. Computer Control and Software.- 2.3. Performance of the System.- 2.3.1. Diffractometer Positioning Accuracy.- 2.3.2. Alignment.- 2.3.3. Parameters of the Focused, Monochromatized Beam.- 2.3.4. Accuracy of Measurement of Diffracted Intensities.- 2.3.5. Tests Using a Graphite Monochromator.- 2.4. Discussion of System Tests and Possible Improvements.- 2.5. Possible Uses of the Systems.- 2.5.1. Macromolecular Crystallography.- 2.5.2. Other Types of Experiments.- 3. Measurement of the Anomalous Scattering Terms for Cesium and Cobalt at Noncharacteristic Wavelengths.- 3.1. The Phenomenon of Anomalous Scattering.- 3.2. Previous Determinations of f? and f?.- 3.3. Principles of the Present Method of Determining the Anomalous Scattering Factors.- 3.4. Experimental Details.- 3.5. Discussion and Correlation of Results with Absorption Spectra.- 4. Use of Anomalous Scattering Effects to Phase Diffraction Patterns from Macromolecules.- 4.1. Previous Work on Phasing Macromolecular Structures.- 4.2. A Quantitative Assessment of Anomalous Scattering Phasing.- 4.2.1. The Effect of Anomalous Scattering on the Diffraction Pattern.- 4.2.2. Criteria Governing the Choice of Wavelengths.- 4.2.3. How Many Measurements Should be Made?.- 4.2.4. A Method for Assessing Various Data Collection Strategies.- 4.2.5. An Example of the Use of the Multiple-Wavelength Phasing Method.- 4.3. Other Data Reduction Considerations.- 4.4. Conclusions.- 5. Progress on the Structure Determination of Gramicidin A: A Case Study of the Use of Synchrotron Radiation in X-Ray Diffraction.- 5.1. The Crystallographic Problem and the Possibility of Its Solution Using Synchrotron Radiation.- 5.2. Preliminary Results of Structural Studies to 3.8-A Resolution Using Synchrotron Radiation.- 5.2.1. The Experiment.- 5.2.2. Data Analysis.- 6. Summary and Discussion.- References.- 18. Application of Synchrotron Radiation to X-Ray Topography.- 1. Introduction.- 1.1. Features of X-Ray Topography.- 1.2. Relevant Characteristics of Synchrotron Radiation Sources for X-Ray Topography.- 1.2.1. Wavelength Spread.- 1.2.2. Angular Spread.- 1.2.3. Lateral Extension.- 1.2.4. Intensity and Polarization Properties.- 1.3. Available and Future Facilities.- 2. Description of Experimental Techniques.- 2.1. White Beam Topography.- 2.2. Monochromatic Topography and Specialized Monochromators.- 2.2.1. Two-Axis Spectrometers.- 2.2.2. Specialized Monochromators.- 2.2.3. Monochromatic Topography.- 2.3. Interferometry.- 2.4. New Developments in Direct Viewing Detectors.- 3. Selected Examples of Applications of Synchrotron Radiation Topography.- 3.1. Recrystallization Experiments.- 3.2. Domain Wall Motion in Magnetic Materials.- 3.2.1. Antiferromagnetic Perovskites KNiF3 and KCoF3.- 3.2.2. Ferromagnetic Alloy Fe-3%Si.- 3.3. Plastic Deformation.- 3.4. Tunable Wavelength Topography in Absorbing Materials.- 3.5. Miscellaneous Applications.- 4. Future Developments.- References.- 19. Inelastic Scattering.- 1. Introduction.- 2. Theory.- 3. Experimental Techniques.- 4. Previous Experiments.- 5. Future Prospects.- References.- 20. Nuclear Resonance Experiments Using Synchrotron Radiation Sources.- 1. Introduction.- 2. Single Nucleus Excitations.- 2.1. Mossbauer Effect.- 2.2. Nuclear Excitation without the Mossbauer Effect.- 2.3. Experimental Results.- 3. Nuclear Bragg Scattering.- 3.1. Proposed Experiments.- 3.2. Experimental Problems.- 4. Conclusions.- References.- 21. Wiggler Systems as Sources of Electromagnetic Radiation.- 1. Introduction.- 2. General Characteristics of Wiggler Radiation.- 2.1. Directionality.- 2.2. Time and Frequency Structure.- 2.3. Monochromaticity.- 2.4. Tunability and Energy Range.- 2.5. Polarization.- 3. Theoretical Considerations.- 3.1. Macroscopic Approach-Classical Field Equations.- 3.2. Microscopic Approach-Quantization of the Field.- 4. Fundamentals of Operation.- 4.1. The Infinite Transverse Wiggler.- 4.1.1. The Flat or Planar Wiggler.- 4.1.2. The Helical or Axial Wiggler.- 4.1.3. The Rotatable Planar Wiggler.- 4.1.4. The Free-Electron Laser (FEL).- 4.2. Wiggler Optics and Influence on Stored Beams.- 4.2.1. Optics.- 4.2.2. Effects on Stored Beams.- 4.3. Practical Design Considerations.- 5. Applications with Examples.- 5.1. The spear Wiggler-A Detailed Example.- 5.1.1. Description of the spear Lattice.- 5.1.2. Description of the Wiggler and Its Operation.- 5.1.3. Description of the Wiggler Transport Line.- 5.1.4. Effects of Wiggler on spear Operation.- 5.2. Characteristics of Other Planned Wiggler Installations.- 5.2.1. Photon Factory at kek, Japan.- 5.2.2. nsls at Brookhaven, USA.- 5.2.3. puls-Adone at Frascati, Italy.- 5.2.4. Pakhra at Moscow, USSR.- 5.2.5. lure-aco at Orsay, France.- 5.2.6. ssrl-spear Undulator.- 5.2.7. Sirius at Tomsk, USSR.- 6. Future Directions, Possibilities, and Conclusions.- References.- 22. The Free-Electron Laser and Its Possible Developments.- 1. Introduction.- 2. Spontaneous Radiation of Relativistic Electrons in Wiggler Magnets.- 3. Elementary Theory of the Free-Electron Laser.- 3.1. Stimulated Radiation by Relativistic Electrons.- 3.2. Classical Theory of Stimulated Radiation in Wiggler Magnets.- 3.3. Principles of Operation of a Free-Electron Laser.- 4. Free-Electron Laser Experiments.- 5. The Free-Electron Laser Operation in an Electron Storage Ring.- 5.1. Principal Characteristics of an Electron Storage Ring.- 5.2. Electron Beam-Free-Electron Laser Interaction.- 5.3. The Free-Electron Laser Operation in a Storage Ring.- 6. Conclusions.- References.