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Magnesium  Fluoride (MgF2)

Magnesium Fluoride crystal has a wide transmission range from 110nm to 7500nm and it exhibits a slight birefringence. The crystal is relatively hard, resistance to water, but sensitive to thermal shock. It can be machined with standard diamond tools and have a good polishing using either aluminum oxide or diamond based polishing papers. It is particularly useful for excimer laser application. Generally, Magnesium Fluoride for laser use is recommended to be oriented along the optic axis to avoid birefringent effects.

 

 

                              Figure 1: External transmittance curve for 7 mm Magnesium Fluoride crystal

 

  Crystal Structure Tetragonal
 
  Lattice Constant (Å) a=4.64, c=3.06
 
  Transparency Range (nm) 110~7500
 
  Crystal Class Positive Uniaxial
 
  Constant of Dispersion (dn/dT)
(/K at 0°C and 632.8nm )
dno/dT=1.24X10-6
dne/dT=0.69X10-6
 
  Melting Point (°C)
1585
 
  Thermal Conductivity (W/(m K) at 300 K):
11.6
 
  Heat Capacity: (J/gK at 276 K):
0.955
 
  Linear Coefficient of Thermal Expansion (20°C)  ( /K)
||C: 13.70X10-6
C: 8.48X10-6
 
  Refractive Indices ne=1.38876, no=1.37698 at 632.8nm
  ne=1.38478, no=1.37319 at 1064nm
 
  Density (g/cm3) 3.1766
 
  Knoop Hardness 415  
  Young's Modulus (GPa) 138.5  
  Shear Modulus (GPa) 54.66  
  Poisson Ratio 0.276  
  Table 1:Magnesium Fluoride Properties
 

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