Astronomy Principles and Practice Fourth Edition.pdf

Polarization phenomena 233
Figure 15.12. The various polarization forms.
form would be detected. Under these conditions, the radiation is said to be unpolarized. If such
radiation could be looked at with extreme time resolution, it would be possible, in principle, to record
the probability of finding a particular polarization form at any instant. The probability distribution so
obtained is unique to naturally occurring unpolarized light.
Under some special circumstances, a collection of atoms can give rise to radiation with a
polarization form which persists over normal experimental time periods. The persistent polarization
ellipse can be described by the same set of parameters which were used to describe the instantaneous
polarization ellipse described earlier (i.e. azimuth, ellipticity and handedness). This type of radiation is
said to be perfectly polarized. The general form of the polarization is elliptical and the extreme forms
of linear and circular also occur.
Many of the interactions of radiation and matter (e.g. reflection, scattering, etc) give rise to
polarization effects. The incident radiation may be unpolarized, but after the interaction, the resulting