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.
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.