ABSTRACT
This chapter applies the resolution of the retardance paradox to rotations of polarization state which occur in nonpolarizing optical systems. If all the diattenuation and retardance is removed from an optical system, systematic polarization changes remain, named skew aberration.
Aberrations can be considered as deviations from the ideal behavior of imaging optical systems, i.e., deviations from the mapping of spherical waves with uniform amplitude and polarization into spherical waves with uniform amplitude and polarization. The main aberration categories are wavefront aberration, apodization (amplitude aberration), and polarization aberration. Wavefront aberration is the variation in optical path length, which is calculated in all the commercial ray tracing programs. Apodization is an amplitude aberration; different rays have different transmittances due to reflection losses and absorption. Polarization aberration, a non-uniform polarization change across wavefronts is divided into (1) diattenuation aberration, which is polarization dependent transmission or reflection, (2) retardance aberration, which is polarization dependent optical path difference, and (3) skew aberration, the polarization change in the absence of diattenuation and retardance aberration.
Skew aberration, is explained using the Pancharatnam/Berry phase. Skew aberration can be significant for high NA optical systems with large fields of view, such as micro-lithography systems.
The effect of skew aberration on point spread functions (PSF) is examined using the Mueller Point Spread Matrix (MPSM) to show how non-polarizing and ideal optical system can have undesired polarization mixing due to skew aberration. Skew aberration’s separate origin and behavior is fascinating. In radially symmetric systems, skew rays have skew aberration but meridional rays do not. Thus, the name skew aberration is applied.
