Thermal diffusivity measurements for two media systems with thermal lens technique in the two lasers mismatched mode

The thermal lens signal produced by a two media system - two thin samples i n a sandwich-like array - is experimentally investigated. A combination of materials presenting self-focusing and self-defocusing lens behavior were s tudied, and their distinct termal diffusivities produced composed thermal l ens with different characteristic times. A model considering alinear combin ation of thermal lenses is proposed. It adjusts very well the experimental data, giving the thermal diffusivities of each component, provided no net a xial heat flux is present. The validity of the model is discussed and it is applied to the characterization of thin films grown on glass substrate.