Sol-Gel Preparation of Ultralow Refractive Index Magnesium Fluoride Optical Films for Broadband Antireflective Coatings

Optical films with ultralow refractive index (n = 1.11) and good transparency were prepared by deposition of nano magnesium fluoride particles on fused silica substrate. It is found the refractive index is related to particle size. With changing the particle size, the refractive index of the magnesium fluoride could be varied from 1.35 to 1.11. Excellent antireflection performance was achieved by the graded-refractive-index films consisting of three MgF2 layers with different refractive index. The average transmittance in the entire visible wavelength region (400 nm-900 nm) was higher than 99.0%. This facile method for ultralow reflective coatings is potentially applicable to various optical devices to dissolve many problems caused by reflection.