Measurement of thermal diffusivity of multilayer optical thin film systems using photoacoustic effect

Two-layer anti-reflection (AR) and five-layer high-reflection (HR) optical coating samples on glass substrate were designed and fabricated, for different evaporation conditions (coating speeds of 10 and 20 E/s, and substrate temperatures of 50, 100, 150, 200°C), using two dielectric materials of MgF₂ and ZnS which have different refractive indices. The through-plane thermal diffusivity were measured using the photoacoustic effect. The results showed that the thermal diffusivity of the sample fabricated in the conditions of 10 E/s and 150°C showed the maximum value and also, it has quite close relations with the microstructure of the film system