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.

CaF2 window capabilities
CaF2 spherical lens capabilities
CaF2 prism capabilities
CaF2 ground blank capabilities

Datasheet – IR Material Calcium Fluoride

Calcium Fluoride Windows
Calcium Fluoride Lenses

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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