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Custom Calcium Fluoride


custom & stock sapphire optical windows

Calcium fluoride (CaF2) is a crystalline optical material with excellent transmission from UV up to the LWIR region. Different grades of calcium fluoride are available:

UV grade has enhanced performance in the UV (and VUV) wavelengths.
IR grade or standard grade calcium fluoride which performs well in the IR regions.
Raman Grade which exhibits minimal fluorescence.
 
Calcium fluoride has numerous beneficial properties including:

  • Low absorption
  • High refractive index homogeneity
  • Chemically inert
  • High damage threshold
  • Physically stable
  • High mechanical strength
  • Insoluble in water

 

Below is a brief summary of calcium fluoride’s properties, a full data sheet is available here.

Transmission range

0.13 to 10µm

Refractive Index

1.39908 @ 5µm

Density

3.18 g/cm3

Melting Point

1360°C

Hardness

Knoop 158.3 (100) with 500g indenter

Operating Temperature

< 800°C in dry conditions

 
Knight Optical supplies high quality calcium fluoride components, including lenses and windows, made to your custom specification. We can offer uncoated and coated calcium fluoride optics, including a broadband antireflective (BBAR) coating. 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 250mm

Form error (@633nm)

< 0.25 waves

Centration /parallelism

< 1 arc minute

Scratch/dig

< 60/40

Typical coatings

Single sided AR @ 2-10µm

 

Uncoated, 1mm thick

With our in-house state-of-the-art metrology laboratory you can be confident that your optical components will meet specification, and you can request a full metrology report. You can find out more about our testing facilities here.

Additional information

  • Calcium flouride is grown by the vacuum Stockbarger technique using either naturally mined or chemically prepared fluorite dependent on the grade
  • Due to its high refractive index homogeneity and low absorption, calcium fluoride makes an ideal substrate for lenses used in high-performance laser systems. The high homogeneity means there will be minimal scattering and deformation of the wavefront.
  • It is traditionally used in an apochromatic lens design, which generally consists of a fluoride lens and two other elements. Apochromatic lenses can correct for both chromatic and spherical aberration, due to this they are widely used in photography where the designation ‘APO’ is used.

Considerations

  • In dry temperatures CaF2 has a maximum operating temperature of 800°C.
  • Calcium fluoride is not readily degraded under normal atmospheric conditions until 600°C where it will start to soften.
  • It is vulnerable to thermal shock at high temperatures.

Typical Applications

Calcium fluoride has uses in applications that work in ultraviolet, visible and/or infrared wavelengths, below are some examples:

Excimer lasers
  • Often used in the lithography industry, excimer lasers are used primarily in the UV wavelengths, typically at 193nm (argon fluoride, ArF) and 248nm (krypton fluoride, KrF). CaF2 (and MgF2) are commonly used as the substrate for excimer laser mirrors.
  • UV grade calcium fluoride is recommended for excimer laser applications as it exhibits less absorption in the UV ranges.
Cryogenically Cooled Thermal Imaging
  • The infrared detector on thermal imaging systems is sometimes cooled, via cryogenic cooling, to keep the detector at a consistent, low temperature to reduce thermal noise. Calcium fluoride is commonly used for such detectors.
  • Standard, IR grade, calcium fluoride would perform best in thermal imaging and FLIR applications.
Raman Spectroscopy
  • Calcium windows are widely used as spectroscopic windows.
  • Knight Optical can supply Raman grade calcium fluoride which has minimal fluorescence and only a singular Raman peak at 321cm—1 which is easy to identify and has a little influence on your measurement.

 

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