氟化镁(MgF2)
Magnesium Fluoride is used for optical elements in the infrared where extreme ruggedness and durability is required. Its useful transmission range is 0.11 μm - 7.5 μm. 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.
OPTICAL
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
PHYSICAL
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)............................... 0.24 at 298 K, 0.362 at 1700 K
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
CHEMICAL
Solubility ..................................................................<0.0002 g/100g water at 0 °C
Molecular Weight.............................................................................................. 62.32
Class/Structure ......................................................Tetragonal, can cleave on C-axis
REFRACTIVE INDEX
....................................................................................(ne)1.43, (no)1.42 at 0.20μm
....................................................................................(ne)1.42, (no)1.41 at 0.23μm
....................................................................................(ne)1.41, (no)1.40 at 0.27μm
....................................................................................(ne)1.40, (no)1.39 at 0.34μm
....................................................................................(ne)1.39, (no)1.38 at 0.56μm
