Material: High grade quartz crystal.
Based on optical activity of crystal quartz, insensitive to
  optical alignment.
Can be simply placed in the beam at normal incidence to
  get the specified polarization rotation.
Optically robust with a high damage threshold.
Suitable for narrow band of wavelengths.
Low cost.

Polarization Rotator Specifications

Dimensions Tolerance: +/- 0.1 mm
Wavefront Distortion: < λ/8 @632.8nm
Rotation Tolerance: < 0.5º
Surface Quality: 10-5 scratch and dig
Coating: AR coating with R < 0.2% at the center wavelength
Holder: Anodized aluminum holder upon request