Leaky Modes in Lithium Fluoride Thick Films Thermally Evaporated on Glass

Polycrystalline thick lithium fluoride (LiF) films have been grown by thermal evaporation on heated glass substrates. Excellent agreement between the values obtained from effective index measurements carried out by the m-line technique and those provided by computer simulations has shown that leaky modes are supported by these dielectric films, as they have a gradually increasing refractive index distribution along the thickness moving from the substrate interface towards the air interface. In some cases the films present also optical anisotropy which results in TM modes having higher effective indices than TE ones.