A brief guide to UV – Visible – Near IR optical materials
When selecting materials for optical applications outside the visible spectrum, there are many different factors to consider. The obvious variables include the transmitted wavelength range, refractive index, achievable surface specifications, and of course, price. However, sometimes there are other parameters which can be overlooked such as: durability in harsh environments, sensitivity to moisture, raw material availability, and in some cases even toxicity.
We have compiled a helpful list of commonly used UV, visible and near IR optical materials with some useful insights and a few things to look out for:
Crystran also holds stock items of many of the materials mentioned here. These can be purchased online please check our website for more information: https://www.crystran.co.uk/products
Calcium Fluoride, CaF2:
Probably the most frequently used IR and UV material when balancing performance and practicality against cost and availability. Inexpensive grades are available for standard IR spectroscopy, but purer (more expensive) material is available for Raman and Far UV (122 to 200 nm) applications.
Barium Fluoride, BaF2:
More mechanically fragile than CaF2 but provides slightly wider transmission into the LWIR. It is frustratingly short of the full 8-12 micron atmospheric bandpass window (by a micron), and is prone to cleaving under thermal shock.
Magnesium Fluoride, MgF2:
One of the two available materials especially suited to upper-VUV applications (the other is LiF). MgF2 is tough, amenable to working and can take a very high cosmetic polish needed for Far UV transmission.
Sapphire, Al2O3:
Sapphire is often used for its extreme toughness and strength and is one of the hardest natural substances on the planet (next to diamond)!
Because of this it is highly resistant to scratches and abrasion whilst having a wavelength range suitable for use in the UV, visible, and near infra-red.
