A guide to selecting CaF2 grades
With a wide transmission band spanning the complete UV to MWIR optical spectrum, Calcium Fluoride is a highly versatile material supporting many applications. Being cubic in crystalline structure, the material is naturally isotropic with respect to both its optical and mechanical properties, allowing it to be used in any orientation without introducing birefringence or non-uniform thermal expansion.
Large material ingots are artificially grown via a vacuum Stockbarger process, enabling the production of lenses / windows / prisms more than 300 mm in diameter. Additionally, given the crystal’s relative hardness and (in)solubility, windows can be polished to an exacting flatness of better than L/20 (0.03 um) and sub-nanometre surface finish (Rq).
Crystal ingots are qualified by purity and categorised into a number of particular grades, as follows. All grades transmit well throughout the IR band, but for UV or spectroscopy applications, material selection can be balanced against cost.
IR Grade – 0.4μm to 10μm
Calcium Fluoride crystal was historically manufactured by fusing naturally mined CaF2. More commonly now, medium quality reagent grade material is used where the most inexpensive material is required. The principal impurities are generally purged further by the crystal growth process but often result in a broad absorption at 0.3μm due primarily to iron, and reduction of transmission at wavelengths shorter than 0.25μm. All Crystran CaF2 is guaranteed free of absorption bands within the Visible and IR spectrum.
UV Grade – 0.19μm to 10μm
Using a higher grade of synthetically produced raw material, Crystran UV grade guarantees transmission through the UV-Visible spectrum as well as the IR. Further absorptions at and 0.19μm to 0.25μm in the IR grade are avoided.
VUV Grade – 0.13μm to 10μm
Using analytical grade synthetically produced raw material, Crystran VUV grade guarantees transmission into the vacuum UV part of the spectrum extending to the theoretical limit for the material.
Eximer Grade – 157nm, 193nm, 248nm selected
Crystran Eximer grade is supplied from pure crystal ingots manufactured from highest purity raw material to ensure the lowest possible absorption for high power laser use. The internal absorption of the crystal is tested by transmission through long path lengths at particular Eximer wavelengths.
Raman Grade – for Raman spectroscopy applications
Crystran Raman grade material is supplied from specially selected ingots not exhibiting any fluorescence emission bands which might interfere with Raman spectroscopy applications.
Crystran has a range of CaF2 windows in IR/UV and Raman grade available in stock for next day shipment. We also have excellent capabilities to manufacture custom parts, please visit our website or email us for more information.
Please visit our website to see if we have the particular optic you are looking for.
https://www.crystran.co.uk/products
If you cannot find the correct part there, or you are wishing to purchase quantities greater than 10 pieces, please contact a member of our sales team.
Sales@crystran.co.uk / +44 (0) 1202307650