Interference effects in Pancharatnam wave plates

The effects of multiple-beam interference within a series of wave plates whose principal axes are rotated with respect to each other are explored. This is done by expanding the formulation of the matrix algebra which was originally developed for multilayer thin-film optics. As an important example, the new method has been applied to a Pancharatnam configuration for achromatic and superachromatic half-wave plates. It is demonstrated that spectral fringes occur in all of the descriptive polarimetric parameters of these devices, i.e., the transmittance, polarizance, phase delay and effective principal axis. Depending on the wavelength resolution and accuracy of any subsequent measurements, any of these spectral fringes may be deleterious to the intended application of such compound wave plates. Removing the effects of the fringes in data reductions requires extreme care in establishing appropriate calibration experiments.