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Barium Fluoride (BaF2)
Barium Fluoride is used in spectroscopic components. Barium Fluoride is often suitable for applications in the passive IR band (8 to 14 μm) and is often used as a viewport window for thermography. For an equivalent thickness the transmission extends approximately 1 micron further into the IR than Calcium Fluoride. Windows intended primarily for IR use and noted as having IR polish may have restricted transmission in the VUV being made from lower purity BaF2 crystal.
The highest quality Barium Fluoride also has application as the fastest known scintillator material and is used in High Energy Physics Experiments.
Products
Windows
Lenses
Prisms & ATR
| Transmission Range | 0.15 to 12 μm |
| Refractive Index | 1.45 at 5 μm (1) |
| Reflection Loss | 6.5% at 5 μm (2 surfaces) |
| Absorption Coefficient | 3.2 × 10⁻⁴ cm⁻¹ @ 6 μm |
| Reststrahlen Peak | 47 μm |
| dn/dT | -15.2 × 10⁻⁶ /°C (2) |
| dn/dμ | 0 |
| Zero Dispersion Wavelength | 1.95 μm |
| Density | 4.89 g/cc |
| Melting Point | 1386 °C |
| Thermal Conductivity | 11.72 W m⁻¹ K⁻¹ @ 286 K |
| Thermal Expansion | 18.1 × 10⁻⁶ K⁻¹ @ 273 K |
| Hardness | Knoop 82 with 500g indenter (4) |
| Specific Heat Capacity | 410 J Kg⁻¹ K⁻¹ (3) |
| Dielectric Constant | 7.33 at 1 MHz |
| Youngs Modulus (E) | 53.07 GPa (3) |
| Shear Modulus (G) | 25.4 GPa (3) |
| Bulk Modulus (K) | 56.4 GPa |
| Elastic Coefficients | C11 = 89.2, C12 = 40.0, C44 = 25.4 (2) |
| Apparent Elastic Limit | 26.9 MPa (3900 psi) (4) |
| Poisson Ratio | 0.343 |
| Solubility | 0.17 g / 100 g water at 23 °C |
| Molecular Weight | 175.36 |
| Class/Structure | Cubic Fm3m (#225), Fluorite structure. Cleaves on (111) |
| µm | No | µm | No | µm | No |
|---|---|---|---|---|---|
| 0.1408 | 1.815 | 0.3663 | 1.4887 | 1.7012 | 1.4655 |
| 0.1452 | 1.7820 | 0.4046 | 1.4844 | 1.9701 | 1.4647 |
| 0.1477 | 1.1.7670 | 0.5461 | 1.4759 | 2.3254 | 1.4636 |
| 0.1500 | 1.6780 | 0.5893 | 1.4744 | 2.6738 | 1.4623 |
| 0.2000 | 1.557 | 0.6438 | 1.4730 | 3.2434 | 1.4602 |
| 0.2652 | 1.5122 | 0.6563 | 1.4727 | 3.4220 | 1.4594 |
| 0.2803 | 1.5066 | 0.7065 | 1.4718 | 5.1380 | 1.4501 |
| 0.2893 | 1.5039 | 0.8521 | 1.4699 | 5.5490 | 1.4473 |
| 0.2967 | 1.5019 | 0.8944 | 1.4694 | 6.2380 | 1.4422 |
| 0.3021 | 1.500 | 1.0140 | 1.4685 | 6.6331 | 1.4390 |
| 0.3130 | 1.4978 | 1.1287 | 1.4678 | 7.0442 | 1.4353 |
| 0.3254 | 1.4952 | 1.3673 | 1.4667 | 7.2680 | 1.4331 |
| 0.3403 | 1.4925 | 1.5295 | 1.4661 | 9.7240 | 1.4051 |
| 0.3466 | 1.4915 | 1.6810 | 1.4656 | 10.346 | 1.3936 |
| 0.3610 | 1.4894 |
Barium Fluoride is grown by vacuum Stockbarger technique. Unlike CaF2, BaF2 is not found in the native state and all material must be synthesised chemically making BaF2 relatively expensive to produce. Barium Fluoride cleaves easily and is highly susceptible to thermal shock. It polishes well and can be etched (5). The highest purity Barium Fluoride VUV material can be qualified as fast scintillator grade. (6)
The highest purity Barium Fluoride VUV material can be qualified as fast scintillator grade. (6)
REFERENCES:
(1) Handbook Optical Constants, ed Palik, V3, ISBN 0-12-544423-0
(2) I.H.Malitson; J.Opt.Soc.Am. Vol52, p1377, 1962
(3) D.Girlich; Elastic Constants of BaF2; Phys.Rev. Vol135, p1826, 1964
(4) S.Ballard et al; J.Opt.Soc.Am. Vol42, p684, 1952
(5) US patent. Chemical polish. 4,040,896 1977
(6) M.Laval et al; Nu. Insts.Meth, V206 p169, 1983