Waveplates and Retarders
A Fresnel Rhomb Retarder is a special kind of optical retarder that produces a phase delay of λ/2 or λ/4 by utilizing internal reflection. Unlike conventional waveplates which function through the birefringence of materials to produce the required phase difference between the two orthogonal polarizations, the Fresnel Rhombs are made of non-birefringent materials and induce the desired phase delay after going through two total reflections. The retardation produced by a Fresnel rhomb depends almost solely on the refractive index and the geometries of the prism, and since the refractive index varies just slightly against a certain wavelength range, the independence of retardation over the wavelength changes is much greater, thus achieving extraordinarily flat retardation throughout a broad wavelength range, which could have been impossible in the case of broadband waveplates made of birefringent materials. This kind of broadband retarder is suitable for applications in diode and fiber applications, broadband, multi-line, or tunable laser sources.
The Fresnel Rhomb Retarder is usually shaped into a right parallelepiped, that is, a right parallelogram-based prism. The angles of the parallelograms are deliberately designed so that each reflection inside the rhomb, with the incident angles carefully chosen, adds a phase difference of precisely 1/8 wavelength between the two orthogonal polarization components, and ultimately resulting in a total phase delay of a quarter of a wavelength in the exiting light. Two quarter-retarders could be cemented together to achieve the effect of using a half-waveplate. The variation in retardance is within 2% across the wavelength range. The Fresnel Rhombs are good substitutes for broadband waveplates and UV waveplates, with extended wavelength bandwidth (broader than the Achromatic Waveplates) from the Ultraviolet to the IR wavelength spectral.
Hangzhou Shalom EO offers Fresnel Rhomb Retarder with either λ/2 or λ/4 retardance, for Ultraviolet, Visible, and LWIR applications. The Fresnel Rhomb Retarders made of BK7 operating at the wavelength range of 350-2300nm, UV Fused Silica ( wavelength range 210-400nm), and ZnSe (wavelength range 2000-15000nm) are procurable. Off-the-shelf products for online shopping are listed in the catalog, while custom products can be provided upon request.