Material: N-BK7 glass or UV grade fused silica (UVFS).
Based on the principle that total internal reflection produces a phase retardation
  between p- and s-components.
The retardation is insensitive to wavelength with an extremely large bandwidth.
λ/2  rhombs are made of two λ/4 rhombs optically contacted.
  λ/4  retarder causes a beam displacement ~ 1.3 x the aperture. λ/2  does not.
Standard aperture 10x10 mm, OD 1.5" (38.1 mm).
Apertures 12x12 mm, 15x15 mm are available upon request.
Standard retarders are uncoated. AR coatings are available upon request.