Waveplates (retardation plates or phase shifters) are made from materials which exhibit birefringence. The velocities of the extraordinary and ordinary rays through the birefringent materials vary inversely with their refractive indices. The 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 a=2pd(ne-no)/l(a-phase difference; d-thickness of waveplate; ne,no-refractive indices of extraordinary and ordinary rays respectively; l-wavelength). At any specific wavelength the phase difference is governed by the thickness of the retarder.

In practice, the thickness required to produce true-zero order waveplate is about tens of micron according to the wavelength, which is too thin to manufacture. For this reason, multiple order waveplate often provides a convenient means of producing the required retardation. Sanctity Laser provides two kinds of multiple orders waveplates- low order and multi order which are classified by the thickness. The retardation value of a multiple order waveplate is strongly dependent on temperature, wavelength, angle of incidence and degree of collimation. Zero order waveplates do not have this dependency. A zero order waveplate is constructed of two multiple order waveplates (optically contacted, cemented or airspaced) with their axes crossed. Thus, the effect of the first plate is canceled by the second, except for the residual difference between them.