Achromatic Waveplate

Unlike standard waveplates, Achromatic Waveplates (Retarders) provide a constant phase shift independent of the wavelength of light that is used. This wavelength independence is achieved by using two different birefringent crystalline materials. An Achromatic Waveplate, AWP, is similar to a Zero-Order Waveplate, which is made from two pieces of Crystal Quartz except that the AWP is composed of one piece of Crystal Quartz and one piece of Magnesium Fluoride, MgF2. Both of these materials are birefringent, however, by proper matching of the birefringent changes in one material with those of the second, retardation changes are minimized as the wavelength changes. This phenomenon produces a waveplate whose change in retardation is extremely small for large variations in wavelength.