|Surface Quality||20/10 S/D||Broad band AR Coating||R<1%@600-900nm|
A Fresnel rhomb retarder is a special kind of optical reterder that produces a phase delay of λ/2 or λ/4 by utilizing internal reflection. Unlike those conventional waveplates which function through the birefringence of materials to produce the required phase difference between the two orthogonal polarization, a Fresnel rhomb is made from non-birefringent material and induces the desired phase delay by two total reflections. Virtually the retardation given by a Fresnel rhomb depends solely on the refrative index and the geometries of the prism, and the refractive index varies only slightly against a certain wavelength range, therefore the independence of retardation over wavelength range is significantly greater, thus achieving steady retardation throughout a broad wavelength range which could have been impossible with birefringent materials. This type of retarders are suitable for use with diode and fiber applications, broadband, multi-line or tunable laser sources.
The Fresnel rhomb retarder is usually shaped into a shaped into a right parallelepiped, that is, a right parallelogram-based prism. The angles of the parallelograms are strictly specified by Shalom EO , so that each reflection, with the incident angle particularly chosen, inside the rhomb adds a phase difference of precisely 1/8 wavelength between the two orthogonal polarization components, resulting in a totoal phase delay of a quarter of a wavelength in the exiting light. And two quarter retarders could be cemented together to achieve the function of a half waveplate. The variation in retardance is within 2% across the wavelength range. Hangzhou Shalom EO offers Fresnel Rhomb Retarders, made from high quality BK7 (wavelength range 350-2300nm), UV Fused Silica ( wavelength range 210-400nm) and ZnSe (wavelength range 2000-15000nm), both customized versions and off-the-shelf products for online shopping are available.
1. Retardance via Wavelength
The graph above illustrates the change in retardation via a wavelength spectral for 350-2300nm, λ/4 Fresnel Rhomb Retarders of BK7.