A speckle-photometry method of measurement of thermal diffusion coefficient of thin multilayer and nanoporous structures

Abstract

Measuring the coefficient of thermal diffusion (CTD) of materials is a relatively complex problem. In this report novel optical method for determining CTD is proposed which is based on an analysis of the spatial-temporal dynamics of the speckle field. The proposed method for measuring the coefficient of thermal diffusion is based on the measurement of an average speed of the speckle-field movement along the specimen surface. Due to statistical nature of speckles, their movement must be also described statistically. Our approach consists in the use of correlation functions describing the degree of change in a speckle-image of some element of the surface in the process of heating or cooling. The advantages of the proposed method are: the technology is fully optical and thermal sensors are not needed, universal and can be customized for specific applications, fast, non-contact and non-invasive; remote measurements from distances of up to several meters or in hard-to-reach positions are possible. Optical measurement of CTD has been carried out for investigation of thin multilayer and nanoporous structures, particularly, those of nanoporous anodic alumina. CTD has been measured for nanoporous anodic alumina structures both modified and not modified with nano-diamonds. Modified films have been established to have larger values of CTD. High resolution allows one to measure spatial inhomogeneities of thermophysical properties of materials. The CTD has been measured along the surface of thin film as well as perpendicular to it.