LiF (Lithium Fluoride) Optics and Crystals

Lithium Fluoride Crystals, with chemical formula LiF, cubic crystal structure, and optical transmission range 0.12um-7um, stand out with their very high UV transmittance and are used for special UV applications. In fact, lithium fluoride has the highest Vacuum Ultraviolet (VUV, which is defined as the UV band from 150nm to 200nm) transmittance and can transmit wavelengths shorter than the 121nm hydrogen Lyman-alpha line, even below 110nm. Among known optical materials so far, lithium fluoride has the highest vacuum ultraviolet transmittance. With the development of deep ultraviolet technologies in recent years, LiF crystals have attracted more and more attention due to their high transmittance and short cut-off wavelength in the deep ultraviolet band. Due to its optimal lattice spacing, lithium fluoride (LiF) is efficient in X-ray spectrometers and is considered an ideal material for monochromator plates.

In addition to producing UV optics, lithium fluoride crystals can also be used to manufacture LiF windows, LiF prisms, and LiF lenses operating in the visible and infrared wavelength range. Lithium fluoride has excellent optical properties, but on the other hand, its physical and chemical properties are not advantageous. It is fragile to thermal shock and will erode in the presence of atmospheric moisture at 400°C and soften at 600°C. Lithium fluoride is prone to cleavage, often along the 100 plane, or along the 110 plane. Due to the vulnerable nature of lithium fluoride, careful consideration should be taken when conditions are humid or when high damage thresholds are required. 

Hangzhou Shalom EO specializes in offering custom UV crystals and optics, this page specifies our LiF crystals (available as crystal ingots, blanks, polished or coated) and LiF optics. Conventionally we utilize the Bridgman-Stockbarger method to grow the lithium fluoride crystals, however, to grow LiF crystals with better microstructure for making monochromator plates, we also use the Kyropoulos method (air-grown). We provide LiF crystals and LiF optics with standard (100), (111) orientations, or other custom orientations. The maximum diameter for our lithium crystal is 100mm. The average optical transmission is >90%@0.2~0.45μm.

Besides the bulk LiF crystals, Shalom EO also supplies custom LiF optical components, comprising (Conventionally the surface quality is 20/10 S/D, higher precision like 10/5 S/D or better can be obtained. Note that lithium niobate is not very easy to polish):

• LiF Optical Windows: Optical windows are transparent optical components that allow light to pass with minimum distortion and loss while protecting the core optical element. Shalom EO provides a series of LiF windows, including flat windows, square windows, stepped windows, and more. The coatings of the windows can be selected, and LiF windows of special shapes such as windows with drilled holes, and wedge windows are available. Surface quality of 10/5 S/D, surface flatness of λ/10, and parallelism <10" can be achieved. 
• LiF Lenses: Optical lenses are transmissive optical components with special surface profiles that converge or diverge light. Shalom EO supplies plano-convex/concave, double convex/concave, meniscus LiF lenses, etc. LiF lenses can be used to manufacture apochromatic lenses when combined with fused silica for UV wavelengths and combined with silicon or germanium for IR applications.
• LiF Prisms: right angle prisms, equilateral prisms, Dove prisms, penta prisms, roof prisms. The LiF prisms are great for beam steering of UV lasers.
• Waveplates: We can provide various LiF waveplates of different retardation values.
• LiF Beam Splitter: Beamsplitters split light into two components according to polarization or splitting ratio.
• Various custom-shaped LiF optics: cylindrical lenses, rod lenses, micro lenses, waveguides, etc.

Transmission Curve of Shalom EO’s LiF2 Crystals: