Waveplates (retardation plates or phase shifters) are made from materials which exhibit birefringence. The velocites of the extraordinary and ordinary rays through the birefringent material varies inversely with their refractive indices. This difference in velocities gives rise to a phase difference when the two beams recombine. In the case of an incident linearly polarized beam this is given by δ=2πd(ne-no)/λ, where α is phase difference; d is thinkness of waveplate; ne, no are refrective indices of extraordinary and ordinary rays respectively; λ is wavelength. At any specific wavelength the phase difference is governed by the thinkness of the retarder.Standard Waveplates