Waveplates(Retarders）
Quarter wave-plates
When applying a linearly polarized beam with the polarization plane aligned at 45deg to the wave-plate's principal plane, the output beam will be circularly polarized. Similarly when applying a circularly polarized beam to a λ/4 wave-plates the output beam will be linearly polarized. When a quarter wave-plates is double passed, i.e. by mirror reflection, it acts as a half wave-plates and rotates the plane of polarization to a certain angle. Quarter wave-plates are widely used in creating circular polarization from linear or linear polarization from circular, ellipsometry, optical pumping, suppressing unwanted reflection, optical isolation and etc.
