Aberrations of a horizontal-vertical depolarizer
Ray-trace equations for uniaxial birefringent materials are used here to derive third-order estimates for aberrations that are produced in imaging through uniaxial plates and horizontal-vertical (HV) depolarizers. An HV depolarizer is a spatial pseudodepolarizer; it converts a uniform input polarization state into a continuum of spatially varying polarization states in an output beam. An HV depolarizer consists of two birefringent wedges whose crystal axes are crossed at 90 deg. The interface between the wedges is included, which leads to a spatially varying retardance that provides the spatial pseudodepolarization. In HV depolarizers, spherical aberration, astigmatism, and image doubling are the principal aberrations for on-axis objects. Only spherical aberration occurs in isotropic plates, while the presence of birefringent wedges introduces astigmatism and image doubling. It is shown that image separation is proportional to the magnitude of the retardance variation.