Calcium Fluoride is used for optical windows, lenses and prisms in transmision range 0.15-9mkm. Degradation due to to moisture in the atmosphere is minimal, and polished surfaces of the CaF2 windows may be expected to withstand several years exposure to normal atmospheric conditions.
Since they are nonaxial, CaF2 crystals do not require consideration of axial direction. Because of CaF2 low refractive index, Calcium Fluoride windows can be used without an anti-reflection coating.
Calcium Fluoride is attacked by atmospheric moisture at 600°C, where it begins to soften. The top use temperature is 800C, when moisture is not present. Irradiation of Calcium Fluoride windows causes some loss in UV transmission. CaF2 is sensitive to thermal shock.
Typical applications: VUV – UV – IR imaging systems, excimer laser windows, Spectroscopic windows and lenses.
ical Formula | CaF2 |
Crystal Class | Cubic, cleaves [111] plane |
Lattice Constant, Å | 5.46 |
Density, g/cm3 (20 °C) | 3.18 |
Molecular Weight | 78.08 |
Dielectric Constant for 105 Hz | 6.76 |
Melting Temperature, K | 1630 |
Thermal Conductivity, W/(m K) at 273 K | 10 |
Thermal Expansion, 1/K at 300 K | 18.9 x 10-6 |
Specific Heat, cal/(g K) at 273 K | 0.204 |
Debye Temperature, K | 510 |
Young’s Modulus, GPa | 75.79 |
Rupture Modulus, GPa | 0.0365 |
Shear Modulus, GPa | 33.76 |
Bulk Modulus, GPa | 83.03 |
Poisson’s Ratio | 0.28 |
Knoop Hardness, kg/mm2 | 178 [100], 160 [110] |