While polarizers operate on the basis of space separation of the ordinary and extraordinary rays, retardation plates (or phase shifters) operates on the basis of velocity difference between the ordinary and extraordinary beams, without space separation. Retardation plates operate as elements changing the state of polarization of optical beams. Because the ordinary and the extraordinary beam pass the plate with different velocities, the phase difference Γ is obtained, between these beams which is proportional to the plate thickness d:
Γ = [2 π (ne − no) d]/λ, where : λ — wavelength
We can define quarter waveplate, half waveplate and for each of them there can me”0”order plate or multi-order plate. “0” order plates is when plate thickness is equal to the phase difference respectively λ/4 or λ/2.
Retardation plates are used for changing and analysis of different states of polarisation. They are especially useful in construction of optical isolators and electrooptic modulators.
We produce retardation plates of „0” and multiple-order from crystalline quartz and MgF2.