We supply both mounted and unmounted versions of Fresnel Rhombs . Fresnel Rhombs are made of BK7 crown glass or UV grade fused silica. A Single Fresnel Rhomb produces a phase shift of 90 (λ/4) as a result of total internal reflection from two surfaces. A Double Fresnel Rhomb produces a phase shift of 180 (λ/2) between the components of light polarized perpendicular and parallel to the plane of incidence. It consists of two cemented single (λ/4) Fresnel Rhombs. The retardation varies only slightly over a relatively wide range of wavelengths. Fresnel Rhombs mounts are cylindrical in shape. Small (end) faces of a Fresnel retarder are adjusted orthogonally to the axis of rotation. Polarizer holder having M27x1 aperture can be used for mounting the Fresnel Rhomb.