The refractive indices of a commercially available specimen of single-crystal MgF2 were determined for both the orinary and extraordinary rays at selected wavelengths from 0.2026 to 7.04 µm. Measurements were made by means of the minimum-deviation method on a precision spectrometer near 19°C. The experimentally determined index values for each polarization were fitted to a three-term Sellmeier-type dispersion equation of the form n2-1 = Σ Ajλ2/(λ2-λJ2), where n is the refractive index, λ is the wavelength of interest, λj is the calculated wavelength of an oscillator, and Aj is the strength of the oscillator at λj. The birefringence was computed as a function of wavelength from the calculated index values obtained for the two polarizations. The dispersion coefficients were also determined for the 0 ray and for the birefringence. The results of this sudy are compared with previously reported work on the refractive properties of MgF2.
Marilyn J. Dodge, "Refractive properties of magnesium fluoride," Appl. Opt. 23, 1980-1985 (1984)