Waveplates (retardation plates or phase shifters) are made from materials which exhibit   birefringence. The velocities of the extraordinary and ordinary rays through the birefringent material vary 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 α =2 π d(n_e-n_o)/ λ，where is α phase difference; d is thickness of waveplate; n_e, n_o are refractive indices of extraordinary and ordinary rays respectively; λ is wavelength. At any specific wavelength the phase difference is governed by the thickness of the retarder.

Ray-photonics  waveplates, including octadic-wave (λ /8), quarter-wave (λ /4), half-wave (λ /2) and full-wave (λ) plates, are widely used in synthesis and analysis of light in various states of polarization. The wavelengths within the range of 240nm~2100nm are all available at Ray-photonics.