Cryogenic complex anistropic permittivity of magnesium fluoride

Abstract

The complex tensor permittivity of MgF2 has been measured using whispering gallery mode and quasi TE0np dielectric post resonator techniques as a function of frequency and temperature. MgF2 exhibits uniaxial anisotropy. At room temperature permittivity component parallel to the anisotropy axis is 4.77 ± 0.2% and the component perpendicular to anisotropy axis is 5.49 ± 0.2%. Dielectric loss tangent component perpendicular to anisotropy axis is approximately 4 × 10−5 and dielectric loss tangent component parallel to anisotropy axis is approximately 7 × 10−5 at 39 GHz and room temperature. Losses at room temperature increase quasi-linearly with frequency. At the temperature of 15 K measured loss tangent values for both the components of the dielectric loss tangent were about 1 × 10−6 at 39 GHz. The RF and microwave losses of magnesium fluoride (MgF2) crystal are low as compared with other commonly used Fluorides. MgF2 is hygroscopic and dielectric losses of this material vary with the contents of water.