Book contents
- Frontmatter
- Contents
- List of illustrations
- List of tables
- Preface
- Acknowledgements
- 1 Introduction
- 2 A description of polarized radiation
- 3 Polarization in astronomy
- 4 Polarization algebra and graphical methods
- 5 Instruments: principles
- 6 Instruments: implementations
- 7 Case studies
- Exercises
- Hints for exercises
- References
- Index
2 - A description of polarized radiation
Published online by Cambridge University Press: 24 November 2009
- Frontmatter
- Contents
- List of illustrations
- List of tables
- Preface
- Acknowledgements
- 1 Introduction
- 2 A description of polarized radiation
- 3 Polarization in astronomy
- 4 Polarization algebra and graphical methods
- 5 Instruments: principles
- 6 Instruments: implementations
- 7 Case studies
- Exercises
- Hints for exercises
- References
- Index
Summary
In this chapter, the main concepts of polarized radiation will be introduced and discussed. These concepts apply at all wavelengths. Electromagnetic radiation will be treated as a continuous travelling-wave phenomenon. Quantum considerations can be postponed until the moment the radiation strikes a detector and is converted into an electrical signal. Ideal detectors are not sensitive to polarization, and, to the extent that a real-life detector can be seen as an ideal one preceded by polarization optics, quantum and polarization considerations can live side by side without the one influencing the arguments concerning the other. Of the electromagnetic wave, only the electric vector will be considered; the corresponding magnetic vector follows from Maxwell's equations.
Astronomical signals are noise-like. These noise-like variations of electric field strength (of the electromagnetic wave) may be passed through a narrow-band filter, so that a ‘quasi-monochromatic’ wave remains. Such a wave contains a very narrow band of frequencies and may be seen as a sinusoidal carrier wave at signal frequency, modulated both in amplitude and phase by noise-like variations. The highest frequencies (the fastest variations) in the modulating noise determine the width of the sidebands around the carrier wave in the frequency spectrum. Any wide-band (‘polychromatic’) signal may be seen as the sum of many quasi-monochromatic signals, all with different carrier frequencies and generally each with its own amplitude and phase modulation.
- Type
- Chapter
- Information
- Astronomical Polarimetry , pp. 8 - 26Publisher: Cambridge University PressPrint publication year: 1996