Material MgF2

Magnesium fluoride is transparent over an extremely wide range of wavelengths. The effective transmission range is 0.11 µm - 7.5 µm(ultraviolet to infrared). Irradiation does not lead to color centers. Magnesium fluoride is a rugged, hard material which is resistant to thermal and mechanical shock. Considerable mechanical shock is needed to cause cleavage which is near perfect when it occurs. The natural form of MgF2 is known as Sellaite. Magnesium fluoride is a positive birefringent crystal grown normally to 135 mm diameter by vacuum Stockbager technique, seeding along the C-axis. Thin layers of MgF2 are frequently applied to the surfaces of optical elements as part of optical coatings such as anti-reflective coatings.


Transmission Range 0.11 to 7.5 microns
Refractive Index N0=1.3836 Ne=1.3957 at 0.405 microns
Reflection Loss 11.2% at 0.12 microns (2 surfaces)
Restrahlen Peak 20 microns
dN/dT +2.3 and +1.7 x 10-6e/ °C at 0.4 microns
Density 3.177 g/cm3
Melting Point 1255 °C
Thermal Conductivity 0.3 W/(m K) at 27 °C
Thermal Expansion 13.7and 8.48 x 10-6e/ °C
Hardness Knoop 415 kg/mm2
Specific Heat Capacity, cal/(g K) at 298 K at 1700 K 0.24 0.362
Dielectric Constant 4.87 parallel and 5.45 perpendicular
Young's Modulus (E) 138.5 GPa
Shear Modulus (G) 54.66 GPa
Bulk Modulus (K) 101.32 GPa
Elastic Coefficients C11=140.2 C12=89.5 C44=56.8, C33=204.7 C13=62.9 C66=95.7
Apparent Elastic Limit 49.64 MPa
Poisson Ratio 0.276
Solubility <0.0002 g/100g water at 0 °C
Molecular Weight 62.32
Class/Structure Tetragonal, can cleave on C-axis


Wavelength, µm 0.20 0.23 0.27 0.34 0.56
Refractive Index (ne) 1.43 1.42 1.41 1.40 1.39
Refractive Index (no) 1.42 1.41 1.40 1.39 1.38