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
Including full-wave (λ), half-wave (λ/2), quarter-wave (λ/4) and octadic-wave (λ/8) plates are widely used in synthesis and analysis of light in various states of polarization. 

Specification of our waveplate as follow:
*Dimension Tolerance:+/-0.20mm to +0.01/-0.01mm 
*ThicknessTolerance:+/-0.20mmto +/-0.005mm 
*Surface Quality:80-50 to 10-5 
*Flatness: at 633nm lambda -- lambda/20per 25mm 
*Clear Aperture:80% -- 100% 
*Parallelism(arc min):3min -- 3sec
*Crystals directional precision:5min to 30sec
*Bevel:0.3+/-0.20mm* 45degree 
*No Bevel 
*Coating R<0.2%  
*Other wavelengths within the range of 200-2300nm are also available upon request.