Birefringence Measurements of Crystal Quartz, Magnesium Fluoride, and Synthetic Sapphire

Accurate birefringence measurements are necessary for designing and producing optics that manipulate polarized light. This is of particular importance for waveplates, which must be polished to a specific thickness, typically with a tolerance on the order of ± 0.25 µm. In this work the birefringence of three common waveplate materials is studied: crystal quartz (over the wavelength range of 320-1650 nm), magnesium fluoride (over the wavelength range of 300-1800 nm), and synthetic sapphire (over the wavelength range of 300-1400 nm). Two independent birefringence measurement methods are reported, which agree with each other to within 5 × 10⁻⁶ for each material. These methods are compared to previously published values, which are within 1.5 × 10⁻⁵ for a large portion of the wavelength range measured for quartz and magnesium fluoride, and within 4 × 10⁻⁵ for sapphire. Additionally, dispersion formulae for each material are determined.