Magnesium Fluoride (MgF2)

Magnesium Fluoride is used for optical elements in the infrared where extreme ruggedness and durability is required. Its useful transmission range is 0.11μm - 7.5μm. 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 135mm diameter by vacuum Stockbarger technique, seeding along the C-axis.

Specifications of MgF2
Transmission Range 0.11 to 7.5μm
Refractive Index no=1.3836, n e=1.3957 @ 0.405μm
Reflection Loss 11.2% at 0.12μm (2 surfaces)
Restrahlen Peak 20μm
dn/dT +2.3 and +1.7 x 10-6/ °C at 0.4μm
Density 3.177 g/cm3
Melting Point 1255 °C
Thermal Conductivity 0.3 W/(m K) at 27 °C
Thermal Expansion 13.7 and 8.48 x 10-6/ °C
Specific Heat Capacity, cal/(g K) 0.24 @ 298K; 0.362 @ 1700K
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