Fluorides have a very broad transmission range from VUV to FIR. They must be chosen especially if the coating materials will also be fluorides, like often used in the VUV/UV or in the MIR/ FIR. The main materials are MgF2 and CaF2.
is the fluoride with the highest resistance to degradation by atmospheric moisture, also at higher temperatures. Its hardness, ruggedness and resistance to mechanical and thermal shock is advantageous for laser windows.
MgF2 has a low birefringence. The windows are fabricated with the optical axis as symmetry axis, minimizing the birefringence effect (c-cut).
LASEROPTIK's MgF2 substrates are very resistant to F-center formation due to their low O2- contamination, which is also expressed by the high VUV transmission.
is used as window as well as substrate material. Compared to MgF2 it has an isotropic structure, lower hardness and it is sensitive to thermal shocks. If CaF2 windows are protected from humidity, they can be used for several years in the laboratory. CaF2 begins to soften at 600 °C, the reaction with atmospheric moisture will take place above this temperature.
Especially in the VUV/UV-range we recommend to use optimized materials for lowest losses like 157 nm- or 193 nm-grade.
The curves on the right show the transmission of the standard UV-grade.