Magnesium Fluoride (MgF2)

Magnesium Fluoride is used for optical elements in both the infrared and ultraviolet. Its useful transmission range is from .19μm; to 6.5μm. The refractive index varies from about 1.48 to 1.3. Magnesium Fluoride is a birefringent material and this aspect should be taken into consideration before selection of this material in an optical design. Janos uses only VUV grade material, with the C-axis oriented to minimize birefringence. Irradiation does not lead to color centers. This VUV material is the least susceptible to radiation induced color centers.

Magnesium Fluoride is one of the lowest index infrared materials, second only to Lithium Fluoride. It is resistant to thermal and mechanical shock. The material is twice as hard as Calcium Fluoride but only half as hard as Germanium. Magnesium Fluoride is significantly more expensive than Calcium Fluoride and Barium Fluoride, but usually not more expensive than Lithium Fluoride. Magnesium Fluoride is similar to Calcium Fluoride in its resistance to water.
 
Product Data -----------------------------------------------------
 
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 at 2.7 μm
Reststrahlen Peak : 20 μm (1)
dn/dT : 2.3 (para) 1.7 (perp) at 0.4 μm (1)
dn/dμ = 0 : 1.4 μm
Density : 3.18g/cc
Melting Point : 1255°C
Thermal Conductivity : 21 (para) 33.6 (perp) W m-1 K-1 at 300K (3)
Thermal Expansion : 13.7 (para) 8.9 (perp) x 10-6 /K (1)
Hardness : Knoop 415
Specific Heat Capacity : 1003 J Kg m-1 K-1
Dielectric Constant : 4.87 (para) 5.45 (perp) at 1MHz (1)
Youngs Modulus (E) : 138 GPa (2)
Shear Modulus (G) : 54.66GPa (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 GPa (7200 psi)
Poisson Ratio : 0.276 (2)
Solubility : 0.0002g/100g water
Molecular Weight : 62.32
Class/Structure : Tetragonal, can cleave on c-axis
 
Refractive Index and Optical Transmittance curve----
Refractive Index(No=Ordinary Ray Ne=Extraordinary Ray):
µm    No Ne µm    No Ne µm    No Ne
0.1137    1.7805   0.1149    1.7420   0.1179    1.6800  
0.1198    1.6510   0.121    1.628 1.632 0.130    1.566 1.568
0.140    1.5095 1.523 0.150    1.480 1.494 0.160    1.461 1.475
0.170    1.448 1.462 0.180    1.439 1.453 0.190    1.431 1.444
0.200    1.423 1.437 0.220    1.413 1.426 0.248    1.403 1.416
0.257    1.401 1.414 0.266    1.399 1.412 0.280    1.396 1.409
0.300    1.393 1.405 0.330    1.389 1.402 0.337    1.389 1.401
0.350    1.387 1.400 0.355    1.386 1.399 0.400    1.384 1.396
0.546    1.379 1.390 0.700    1.376 1.388 1.087    1.373 1.385
1.512    1.370 1.382 2.000    1.368 1.379 2.5    1.364 1.375
3.030    1.360 1.370 3.571    1.354 1.364 4.000    1.349 1.359
4.546    1.341 1.350 5.000    1.334 1.343 5.556    1.324 1.332
6.060    1.314 1.321
Optical Transmittance Curve of MgF2 (Reference Data):
lithium-fluoride-lif Transmittance
 
Special properties of MgF2-----------------------------------

Its birefringence should be taken into consideration before selection of this material in an optical design..

It is resistant to thermal and mechanical shock.

It is twice as hard as CaF2 but only half as hard as Ge.

It is significantly more expensive than CaF2 and BaF2,but usually not more expensive than LiF.

MgF2 is diamond turnable.

Typeical application:Thermal imaging, Astronomical, Excimer laser applications..

Products manufactured:Lenses, Aspheric lenses, Windows, Optical Beamsplitters, Optical Filters, Wedges, Prisms.

Surface finish:Polishes of 10-5, or 20-10 scratch-dig are achieved at extra costs respectively mainly for UV applications. Typical specifications for surface quality in the visible and near infrared regions are a 40-20 and 60-40 scratch dig in the 3 to 7μm range. MgF2 is diamond turnable.

Surface figure:In the UV and Visible spectral regions, surface figure ranges from 1/10 wave to 1/2 wave @0.6328μm. In the infrared, typical required surface figure ranges from 1/2 wave to 2 waves @0.6328μm and are specified depending on the system performance requirements.

AR coating options:Magnesium Fluoride can be AR coated for use in the infrared but generally without much improvement in transmission due to its low index of refraction and already high transmission.
Product Notes:------------ --------------------------------------

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

Data provided is extracted from our technical handbook of materials. While every attempt has been made to verify the source of the information, ultiQuest Technology accept no responsibility for accuracy of data

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