Custom Lithium Fluoride
Lithium Fluoride (LiF) is a colourless crystalline material grown by vacuum Stockbarger technique. It has a wide transmission spectrum from the VUV to IR, but it is most commonly used for specialised UV optics due to its deep UV transmission.
Below is a brief summary of lithium fluoride’s optical properties, a full data sheet is available here.
|
Transmission range |
0.12 to 6µm |
|
Refractive Index |
1.392 @ 0.6µm |
|
Density |
2.639 g/cm3 |
|
Melting Point |
848°C |
|
Hardness |
Knoop 102 with 600g indenter |
Knight Optical supplies high quality lithium fluoride components, including windows, lenses and prisms, made to your custom specification. We can offer uncoated and coated optics, including broadband antireflective (BBAR) coatings. Our typical manufacturing specifications are listed below however we are always expanding our capabilities so if your requirements are not mentioned below, please contact our technical sales team who will guide you through your enquiry.
|
Diameter |
< 5mm to 100mm + |
|
Form error (@633nm) |
< 0.25 waves |
|
Centration /parallelism |
< 1 arc minute |
|
Scratch/dig |
< 20/10 |
|
Typical coatings |
BBAR @ 1-6µm DLC @ 1-6µm |
With our in-house state-of-the-art metrology laboratory you can be confident that your optical components will meet your requirements. You can find out more about our testing facilities here.
Additional Information
- Lithium fluoride has the lowest refractive index of the commonly used infrared materials.
- It also has the most extreme UV transmission of the infrared materials, transmitting beyond the hydrogen Lyman-alpha line at 121nm.
Considerations
- Though largely insoluble in water, lithium fluoride degrades by atmospheric moisture at around 400°C, whilst in dry conditions it can be used up to 600°C.
- LiF cleaves easily during manufacture, so steep radii can cause surface tearing and damage to the optic. Extreme care needs to be taken.
- It is sensitive to thermal shock from a rapid change in temperature which can cause cleavage in the material.
Typical Applications
X-Ray Monochromator Plates
- The particular lattice gaps in lithium fluoride’s crystalline structure means that for specific wavelengths, and at certain incident angles, it will reflect radiation (x-rays). This is known as Bragg Diffraction. When these reflected x-rays interfere constructively they form a Bragg peak of intense radiation. Using a plate of lithium fluoride, a monochromatic (single) beam of x-ray can be selected.
Transmission windows
- Due to its excellent transmission down to the VUV range, lithium fluoride windows are often used in VUV and excimer lasers.
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