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Magnesium Fluoride MgF2
Magnesium Fluoride transmits well into the VUV region to the hydrogen Lyman-alpha line (121nm) and beyond. Magnesium Fluoride is used mostly for UV optics and is excellent for Excimer laser applications. We normally cut and orient windows with the optic axis (the c-axis) [001] normal to the surface which is parallel with the (001) plane for minimum bifrefringence. The a-cut which is equivalent to b-cut can be selected if required for maximum birefrigence.
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Windows
Lenses
| Transmission Range | 0.12 to 7 μm (1) |
| Refractive Index | No = 1.413 at 0.22 μm (4) |
| Reflection Loss | 5.7% at 0.22 μm (2 surfaces) |
| Absorption Coefficient | 40 x 10-3 cm-1 @ 2.7 μm |
| Reststrahlen Peak | 20 μm (1) |
| dn/dT | 2.3 (para); 1.7 (perp) @ 0.4 μm (1) |
| dn/dμ | 1.4 μm |
| Density | 3.18 g/cc |
| Melting Point | 1255°C |
| Thermal Conductivity | 21 (para); 33.6 (perp) W m-1 K-1 @ 300 K (3) |
| Thermal Expansion | 13.7 (para); 8.9 (perp) x 10-6/K (1) |
| Hardness | Knoop 415 |
| Specific Heat Capacity | 1003 J Kg-1 K-1 |
| Dielectric Constant | 4.87 (para); 5.45 (perp) @ 1 MHz (1) |
| Young's Modulus (E) | 138 GPa (2) |
| Shear Modulus (G) | 54.66 GPa (2) |
| Bulk Modulus (K) | 101.32 GPa (2) |
| Elastic Coefficients | C11 = 140; C12 = 89; C44 = 57; C13 = 63; C66 = 96 (2) |
| Apparent Elastic Limit | 49.6 MPa (7200 psi) |
| Poisson Ratio | 0.276 (2) |
| Solubility | 0.0002 g/100 g water |
| Molecular Weight | 62.32 |
| Class/Structure | Tetragonal P42/mnm (#136), Rutile structure. Can cleave on c-axis but not easily |
| μm | No | Ne | μm | No | Ne | μm | No | Ne |
|---|---|---|---|---|---|---|---|---|
| 0.1146 | 1.7350 | 1.7295 | 0.190 | 1.431 | 1.444 | 0.546 | 1.379 | 1.390 |
| 0.1149 | 1.7420 | 1.7215 | 0.200 | 1.432 | 1.437 | 0.700 | 1.376 | 1.388 |
| 0.1156 | 1.7235 | 1.7080 | 0.220 | 1.413 | 1.426 | 1.087 | 1.373 | 1.385 |
| 0.1168 | 1.7000 | 1.6905 | 0.248 | 1.403 | 1.416 | 1.512 | 1.370 | 1.382 |
| 0.1179 | 1.6800 | 1.6750 | 0.257 | 1.401 | 1.414 | 2.00 | 1.368 | 1.379 |
| 0.1198 | 1.6510 | 1.6520 | 0.266 | 1.399 | 1.412 | 2.50 | 1.364 | 1.375 |
| 0.1215 | 1.6280 | 1.6320 | 0.280 | 1.396 | 1.409 | 3.030 | 1.360 | 1.370 |
| 0.130 | 1.566 | 1.568 | 0.300 | 1.393 | 1.405 | 3.571 | 1.354 | 1.364 |
| 0.140 | 1.5095 | 1.523 | 0.330 | 1.393 | 1.402 | 4.00 | 1.349 | 1.359 |
| 0.150 | 1.480 | 1.494 | 0.337 | 1.389 | 1.401 | 4.546 | 1.341 | 1.350 |
| 0.160 | 1.461 | 1.475 | 0.350 | 1.387 | 1.400 | 5.00 | 1.334 | 1.343 |
| 0.170 | 1.448 | 1.462 | 0.355 | 1.386 | 1.399 | 5.556 | 1.324 | 1.332 |
| 0.180 | 1.439 | 1.453 | 0.400 | 1.384 | 1.396 | 6.060 | 1.314 | 1.321 |
Magnesium Fluoride is grown by vacuum Stockbarger technique in ingots of various diameters. Magnesium Fluoride is a tough material and polishes well. Therefore, it can be worked to the highest standards. MgF2 is slightly birefringent and usually supplied with the optic axis cut perpendicular to the window faces.
REFERENCES:
(1) Duncanson et.al. Proc.Phys.Soc. V72, p1001, 1958
(2) Kandil et.al. J.App.Phys. V52, p749, 1981
(3) Kashnow & MCarthy, J.Phys.Chem. V30, p813, 1969
(4) Laporte et. al. J.Opt. Soc. Am. V73, No 8, p1062
