Fresnel rhombs are excellent achromatic retarders with Low Temperature Sensitivity and Broader Wavelength Range than Waveplate,it changes retardance with wavelength arises only from the change in refractive index.Like broadband waveplates providing uniform λ/4 or λ/2 retardance over a wider range of wavelengths than possible with birefringent waveplates,fresnel rhombs are ideal retardation plates replacement for broadband, multi-line or tunable laser sources.
DIEN TECH provides half wave retarders which is made by combining two quarter wave rhombs.