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UV&IR Calcium Fluoride (CaF2) Windows

UV&IR Calcium Fluoride (CaF2) Windows

Calcium fluoride is often used in spectroscopic windows […]

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CaF2-Window UV&IR Calcium Fluoride (CaF2) Windows
Calcium Fluoride Windows

Calcium fluoride is often used in spectroscopic windows and lenses due to its high transmission from 200 nm to 7μm. Its low absorption and high damage threshold makes it a popular choice for excimer laser optics. Calcium fluoride’s low index of refraction allows it to be used without an anti-reflective coating. The Knoop hardness of calcium fluoride is 158.3. TECHSPEC® Calcium Fluoride (CaF2) Windows manufactured from vacuum UV grade calcium fluoride are commonly found in cryogenically cooled thermal imaging systems.

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CaF2 (Calcium Fluoride) is a cubic crystal with an excellent transmission from 130 nm to 10 μm and has widespread applications as transparent windows in the ultraviolet and infrared spectra.Recently, CaF2 windows found a wide use for broadband continuum generation (white light generation) pumped by femtosecond lasers.

Application of CaF2 Window

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The high damage threshold and low UV absorption of calcium fluoride make uncoated CaF2 windows a good choice for excimer laser optics. These specialty UV laser systems are used in micro-machining devices and in eye surgery, and we ensure that each of our CaF2 windows is precisely polished and features the high surface quality necessary for these precise laser applications. Our quality check is second to none, and we use state of the art metrology equipment to check that every window which levels our factory fully meets all applicable standards.

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Orientation of Calcium Fluoride Windows

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The cubic crystalline structure of CaF2 means that a calcium fluoride window will have different properties depending on how it is cut. Our standard calcium fluoride windows are randomly cut. For broadband continuum generation (white light generation), we are also able to supply windows cut along the [001] axis. Please contact us to discuss the specific need of your application.

Properties of CaF2 windows

The optical properties of CaF2 are comparable to that of BaF2, but with a Knoop hardness of 158.3 it is almost twice as hard. It is also significantly lighter: the density of CaF2 is 3.18 g/cm3, vs 4.89 g/cm3 for barium fluoride. CaF2 optics tend to be more economical than their BaFcounterparts, as, unlike barium fluoride, the optical crystalline substrate can be found in nature.  Pure calcium fluoride is transparent, but since most CaF2 used for optical windows is naturally mined it may have absorption bands around 300 nm, due to impurities. Calcium fluoride and has a low refractive index (1.39908 at 5 μm).

Environmental Reactions

Calcium fluoride is resistant to water, HF, and many other acids, although it will dissolve slowly under contact with nitric acid.   At room temperature and 100% humidity, a CaF2 window won’t fog, and a polished surface should not degrade under normal working conditions.  At temperatures exceeding 600 C you should expect significant degradation in the presence of moisture or humidity, but in a dry environment these windows can be used up to 1000 C.

Temperature Dependence of CaF2 windows

In dry conditions CaF2 does not experience significant degradation of form or optical properties until about 800 C.  At high temperatures it may be prone to thermal shock, but it is less sensitive to temperature changes than BaF2. The coefficient of thermal expansion is 18.85 x 10-6/C, and melting point 1360°C.