Retarders This is a class of optical devices which introduce a phase difference between extra-ordinary and ordinary rays. These are in the form of plates. - ppt video online download
Polarization of Light by Half Wave Plate
Generalized elliptical retarder design and construction using nematic and cholesteric phase liquid crystal polymers
Polarization of Light by Quarter Wave Plate
Understanding Waveplates and Retarders | Edmund Optics
Introduction to Waveplates and Retarders
Polarized Light Microscopy - The Quarter Wavelength Retardation Plate | Olympus LS