Optimization of thermal evaporation for continuous silver films and their application for non-polarizing optical components

Abstract

Ultra-thin metal films possess big possibilities in design and manufacture of multilayer structures with sophisticated spectral performances over wide wavelength ranges. Continuous ultra-thin metal film has a smaller depolarizing effect than dielectric film, due to this reason the amount of total coating thickness and layers number in non-polarizing coatings can significant reduced. Nevertheless, depending on the substrate temperature, the deposition rate, the thickness, ultra-thin metals films can form continuous or discontinuous nano island structures. When optical components are used at oblique angles of incidence, the reflectance and transmittance of thin film exhibit strong polarization effects. However, for many applications, the polarization effects are undesirable and should be reduced. Non-polarizing coatings are widely used for a variety of photonic applications ranging from interferometry and holography. Their aim is to divide incident light into transmitted and reflected beams in a certain ratio for both s- and p-polarized light. In present work, different combinations of deposition parameters were investigated for silver thermal evaporation. Various dependencies on silver thin metal film formation are shown. The dependence on metal thickness showed different regime of film formation. Microstructure and optical properties were investigated by using of atomic force microscope, ellipsometry and spectrometer measurement A novel plate metal–dielectric three-layer, broadband nonpolarizing beam splitter (nPBS) with an ultra-thin silver film was designed.