Microscopic thermoelastic characterizations by interferometric photothermal microscopy I. EXPRESSION OF THE INTERFEROMETRIC SIGNAL

International audienceSome publications have demonstrated that local thermoelastic behavior in materials can be revealed using a photothermal microscope coupled with an interferometer, but up to now the quantitative data that can be extracted from these measures are not established clearly. We present analysis of the signals, numerical simulations, and experimental results which demonstrate that the thermal diffusivity, the elastic anisotropy, and the principal directions of anisotropy orientation can be obtained with a microscopic resolution. The thermoelastic microscope ͑see Ref. 1 for a figure͒ uses a probe beam crossing a Nomarski interferometer to detect the periodic thermoelastic elevation u ˜ z produced by the optical absorption of a modulated pump beam. The Wol-laston prism of this Nomarski separates the probe beam ͑in-tensity I 0) in two beams, after reflection on the sample surface and partial recombination, interference phenomenon sensitive to the local altitude variation ⌬h between the two sample locations where the beams are focused shall be detected with a photodiode. The intensity of the interference term is driven by the phase shift ␾ between the two probes ␾ϭ 4␲ ␭ ͑ ⌬hϩ␪ • d ͒. ͑1