Waveplates (retardation plates or phase shifters) are made from materials which exhibit birefringence, we usually use Quartz or Quartz+BK7. There are several kinds of waveplates, Multi-Order waveplate, zero order waveplate, true zero order waveplate , Achromatic waveplate and dual wavelength waveplate. Our standard size is dia10mm, 12.7mm, 15mm, 20mm, 25.4mm and 30mm. Of course, other size and coating are available upon request.