Lithium Fluoride (LiF)

Lithium Fluoride has the lowest index of refraction of all the common infrared materials. LiF is slightly plastic, and has a relatively high thermal expansion coefficient. It is also the most expensive of the Fluoride series of crystals.

 

Property Specification
Transmission Range 0.121µm to 5.0µm
Density 2.639 g/cm3
Thermal Expansion 37 x 10-6 /°C
Surface Finish Typical specifications for surface quality in the infrared are a 40-20 scratch dig in the 0.75 to µm spectral region and 60-40 or 80-50 scratch-dig for the 3-7µm area depending upon system performance requirements. LiF is diamond turnable.
Surface Figure In the infrared, typical surface figure ranges from 1/2 wave to 4 waves @ 0.6328µm depending upon system performance requirements.
AR Coating Options LiF 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
Typical Applications Thermal imaging, Astronomical, Excimer laser applications.
Products Manufactured Lenses, Aspheric lenses, Windows, Wedges, Prisms.

 

Wavelength (µm)
Index of Refraction (n)
1.0
1.387
2.0
1.379
3.0
1.367
4.0
1.349
5.0
1.327
5.8
1.304