Book contents
- Frontmatter
- Dedication
- Contents
- Preface
- Acknowledgments
- Acronyms
- 1 Introduction
- 2 The macroscopic Maxwell equations and monochromatic fields
- 3 Fundamental homogeneous-medium solutions of the macroscopic Maxwell equations
- 4 Basic theory of frequency-domain electromagnetic scattering by a fixed finite object
- 5 Far-field scattering
- 6 The Foldy equations
- 7 The Stokes parameters
- 8 Poynting–Stokes tensor
- 9 Polychromatic electromagnetic fields
- 10 Polychromatic scattering by fixed and randomly changing objects
- 11 Measurement of electromagnetic energy flow
- 12 Measurement of the Stokes parameters
- 13 Description of far-field scattering in terms of actual optical observables
- 14 Electromagnetic scattering by a small random group of sparsely distributed particles
- 15 Statistically isotropic and mirror-symmetric random particles
- 16 Numerical computations and laboratory measurements of electromagnetic scattering
- 17 Far-field observables: qualitative and quantitative traits
- 18 Electromagnetic scattering by discrete random media: far field
- 19 Near-field scattering by a sparse discrete random medium: microphysical radiative transfer theory
- 20 Radiative transfer in plane-parallel particulate media
- 21 Weak localization
- 22 Epilogue
- Appendix A Dyads and dyadics
- Appendix B Free-space dyadic Green's function
- Appendix C Euler rotation angles
- Appendix D Spherical-wave decomposition of a plane wave in the far zone
- Appendix E Integration quadrature formulas
- Appendix F Wigner d-functions
- Appendix G Stationary phase evaluation of a double integral
- Appendix H Hints and answers to selected problems
- References
- Index
- Plate Section
9 - Polychromatic electromagnetic fields
Published online by Cambridge University Press: 05 July 2014
- Frontmatter
- Dedication
- Contents
- Preface
- Acknowledgments
- Acronyms
- 1 Introduction
- 2 The macroscopic Maxwell equations and monochromatic fields
- 3 Fundamental homogeneous-medium solutions of the macroscopic Maxwell equations
- 4 Basic theory of frequency-domain electromagnetic scattering by a fixed finite object
- 5 Far-field scattering
- 6 The Foldy equations
- 7 The Stokes parameters
- 8 Poynting–Stokes tensor
- 9 Polychromatic electromagnetic fields
- 10 Polychromatic scattering by fixed and randomly changing objects
- 11 Measurement of electromagnetic energy flow
- 12 Measurement of the Stokes parameters
- 13 Description of far-field scattering in terms of actual optical observables
- 14 Electromagnetic scattering by a small random group of sparsely distributed particles
- 15 Statistically isotropic and mirror-symmetric random particles
- 16 Numerical computations and laboratory measurements of electromagnetic scattering
- 17 Far-field observables: qualitative and quantitative traits
- 18 Electromagnetic scattering by discrete random media: far field
- 19 Near-field scattering by a sparse discrete random medium: microphysical radiative transfer theory
- 20 Radiative transfer in plane-parallel particulate media
- 21 Weak localization
- 22 Epilogue
- Appendix A Dyads and dyadics
- Appendix B Free-space dyadic Green's function
- Appendix C Euler rotation angles
- Appendix D Spherical-wave decomposition of a plane wave in the far zone
- Appendix E Integration quadrature formulas
- Appendix F Wigner d-functions
- Appendix G Stationary phase evaluation of a double integral
- Appendix H Hints and answers to selected problems
- References
- Index
- Plate Section
Summary
The definition of a purely monochromatic electromagnetic field given in Section 2.3 implies that the time dependence of the complex vectors ε (r,t) and H(r,t) is fully described by the complex-exponential factor exp(—iωt) with a fixed angular frequency ω. This can be a good model for beams generated by certain types of laser, but not for the majority of natural and artificial electromagnetic fields. In reality, the electromagnetic field is typically polychromatic, i.e., is a superposition of a (possibly very large) number of monochromatic fields with different angular frequencies distributed over a given range [ωmin, ωmax]. Furthermore, in many cases the amplitudes of the complex electric and magnetic fields representing the component with an angular frequency ω are not constant but rather fluctuate in time, albeit much more slowly than the factor exp(—iωt). Then the resulting polychromatic field is said to consist of quasi-monochromatic components. The range of angular frequencies [ωmin, ωmax] of monochromatic or quasi-monochromatic components can be relatively narrow for some artificial sources of light. However, it can also be very wide, the solar radiation and the light produced by incandescent lamps being prime examples.
Given the ubiquity of polychromatic electromagnetic fields in natural and artificial environments, it is essential to analyze how the results of Chapters 7 and 8 can be generalized to account for a mix of different angular frequencies and/or random fluctuations of the amplitudes of the constituent complex fields.
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- Electromagnetic Scattering by Particles and Particle GroupsAn Introduction, pp. 89 - 98Publisher: Cambridge University PressPrint publication year: 2014