Magnesium Fluoride (MgF2)
 

(Link to CaF2 Specification)

 

MATERIAL: Magnesium Fluoride (MgF2)
APPLICATIONS: UV and Vacuum UV windows, lenses, polarisers,

PROPERTY VALUE
   
-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 and dN./dT +2.3 and +1.7 x 10-6/ °C at 0.4 microns
   
-PHYSICAL-  
Density 3.177 gm/cc
Melting Point 1255 °C
Thermal Conductivity 0.3 Wm-1 °K-1 at 27 °C
Thermal Expansion 13.7and 8.48 x 10-6/ °C
Hardness Knoop 415
Specific Heat Capacity  
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 gm/100gm water at 0 °C
MolecularWeight 62.32
Class/Structure Tetragonal, can cleave on C-axis

NOTES
Magnesium fluoride is a positive birefringent crystal grown normally to 135mm diameter by vacuum Stockbarger technique, seeding along the C-axis. The main application is in the Vacuum UV region and so particular care is taken with the raw material and each ingot is sampled and tested to achieve a minimum transmission of 40% at Lyman-alpria (0.1216 micron) through a 2mm window, and all ingots are tested with a deuterium lamp for the weak fluorescence which can occur. Magnesium fluoride is a proven window material for Eximer lasers and resistance to laser damage is good, nevertheless permanent colour centre formation does occur.

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. A hot pressed polycrystalline form of MgF2 was developed by the Eastman Kodak company and known as lrtran-1.
Magnesium fluoride doped with cobalt is under investigation for laser systems.

 


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