For quantitative photothermal investigation of both thermal and optical properties of thin films it is necessary to calibrate the observed signals. For thermoreflectance measurements this is the absolute surface temperature rise while for photothermal displacement measurements the slope of the sample surface deformation must be related to the energy absorbed from the heating beam. Such calibration is obtained by imaging the spatial distribution of ac current heating in metallic layers incorporated into a thin film system. We present experimental evidence that results from both techniques and can serve as a direct measure for the squared current density in the film. The surface temperature and thermoelastic response was calculated using simple one- dimensional models for the surface temperature and thermoelastic expansion. It is demonstrated that the method is well suited for an accurate absolute calibration of photothermal thin film measurements. The possible use of the Joule heating methods for thermal characterization of thin films and imaging of thin film microstructures is discussed.
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