Material: High grade quartz crystals.
Designed to give a retardation of the exact fraction of a
  wavelengh.
Made of an extremely thin single crystal plate.
Optically robust with a high damage threshold.
Large wavelength and temperature bandwidths.
Suitable for high power broadband applications.

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True Zero-Order Waveplate Specifications

Dimensions Tolerance: +/- 0.1 mm
Wavefront Distortion: < λ/8 @632.8nm
Retardation Tolerance: < λ/300
Surface Quality: 20-10 scratch and dig
Coating: AR coating with R < 0.2% at the center wavelength
Holder: Anodized aluminum holder
Clear Aperture: > Diameter - 2.0mm (mounted)

Structure and
the optical axis