Single-layer film regulation characteristics of particle pollutant scattering from optical surfaces

In order to reduce the light scattering loss of particle pollutants on the surface of ultra-precision low-loss optical elements, a method of adjusting the surface field intensity distribution by depositing a monolayer film on the optical surface was proposed. The electric field intensity of particle pollutants with a radius of 100 nm above the surface of monolayer SiO₂ and monolayer TiO₂ thin films of different thicknesses on the ultra-smooth optical surface of K9 glass was theoretically analyzed. The theoretical analysis results show that when the thickness of SiO₂ thin film is 137.4 nm and the thickness of TiO₂ thin film is 12.3 nm, the surface particle contaminant has the lowest electric field intensity. On this basis, the total scattering loss (S) and bidirectional reflection distribution function (BRDF) of particle pollutants on the surface of optical element, films for SiO₂ with a thickness of 137.4 nm and TiO₂ with a thickness of 12.3 nm were calculated respectively. The calculated results show that when the light with a wavelength of 632.8 nm is vertically incident, monolayer SiO₂ film and monolayer TiO₂ film can effectively reduce the BRDF of the surface particles, and the total scattering on the surface of K9 glass can be reduced by 12.40% and 25.04% respectively. The effectiveness of single-layer SiO₂ thin film for reducing the scattering of surface particle pollutants is verified by experiments.