Optical Constant Test And Evaluation Of Inhomogeneous Films

The gradient index thin film is also called inhomogeneous film. Because it eliminating the surface of different material, it will be widely used in the field of AR coating, beam splitter, polarizing elements, short-wave pass filter, minus filters and so on. But the factor of influencing the reflectivity of inhomogeneous film is uncertain, so measuring the optical constant of inhomogeneous film’s refractive index is difficult.In this paper, the spectrophotometry method of inverting the refractive index profile of inhomogeneous films is mainly discussed. How to equivalent a inhomogeneous film with a gradient thin film is explored. The factor of influencing the reflectivity of inhomogeneous films is analyzed in theory. Inverted a profile of inhomogeneous film which base is K9glass using the reflectivity of the film; Evaluate the optical constant of inhomogeneous film.With the study above in theory and simulate using programming, it turned out that:1. The evaluate criterion of stratified equivalent is the error between linear gradient refraction index film and gradient refraction index film. When the refraction index is from1.4to2.0, the thickness is less than400nm, once the gradient index films reached the layers of12the error between linear gradient refraction index film and gradient refraction index film is less than0.02%.2. The inside refraction index called n(?), lateral refraction index called n(?), and the geometric thickness are three factors of mainly influencing the reflectivity of inhomogeneous film. The maximum and minimum of reflection increase with the increasing of na; If nb increased the amplitude of the reflectance profile increasing also; With the increasing the geometric thickness the reflectivity will be changed as the normal film. 3. By using the Particle Swarm Optimization (PSO), it is possible to get the refraction index profile of inhomogeneous film quickly, the error between linear gradient refraction index film and gradient refraction index film is less than0.5%.4. There is not big impact of extinction coefficient by evaluate the extinction coefficient of inhomogeneous film.