MgF2 | Optical characterization of thin films

MgF2(Magnesium Fluoride) is known as a material with one of the lowest refractive indexes in the VIS region, and is used in many thin film applications. It has a refractive index of 1.38 at 550 nm and a transmittance range from below 220 nm to 2 μm. Using a heating substrate improves the film hardness and the adhesion to the substrate.

Despite its optical properties, this material often produces from severe spitting and sometimes is the main reason for surface defects in coatings. The reasons for this tendency include the physical properties, form, and shape of the material, as well as the deposition rate, degree of preconditioning, EB power, evaporation program, impurity content, void volume, hole-drilling, degree of vacuum, etc.

The most popular form for MgF2 is fused granules. However, we have developed sintered pellet-type MgF2 evaporation materials that have a reduced tendency for spitting. The structures of these sintered pellets are specifically designed for use with high-power EB irradiation, thereby reducing the preconditioning time and increasing the production speed. Another concern is the increasing surface quality requirement for optical components. We address this specifically with our MgF2 sintered pellets, which are particularly suited to applications with strict surface quality requirements, where even minute pinholes must not be present.