Thermal diffusivity measurement of two-layer optical thin-film systems using photoacoustic effect

In this study we designed and developed two-layer antireflection (AR) optical coating samples on glass substrates, using different evaporation conditions of coating rates and substrate temperatures for two dielectric materials. MgF2 and ZnS. with different refractive indices. The through-plane thermal diffusivity of these systems was measured using the photoacoustic effect. The optical thicknesses of MgF2 and ZnS layers were fixed at 5 lambda/4 (lambda = 514.5 nm) and lambda, respectively, and the thermal diffusivities or the samples were obtained from the measured amplitude of the photoacoustic signals by changing the chopping frequency of the Ar+ laser beam. The results demonstrated that the thermal diffusivity of the sample fabricated under the conditions of 10 Angstrom . s(-1) and 150 degrees C had the maximum value and that the results were directly related to the microstructure of the film system.