Thermo-elastic properties characterization by photothermal microscopy

A photothermal microscope devoted to microscopic thermal and thermo-elastic characterizations is presented. In thermal configuration, the sample is heated by an intensity modulated laser beam and the periodic temperature increase at the sample surface is detected using the photoreflectance technique. In thermo-elastic configuration, the periodic elevation of the sample surface is measured using a Nomarski interferometer. The spatial resolution is micrometric, the sensivity is better than 10(-3) K/rootHz in thermal configuration and 10 pm/rootHz in the interferometric one. Typical photoreflectance thermal properties measurements are performed to evaluate the performance of the instrument. In thermo-elastic configuration, the interferometric signal has to be carefully analyzed to remove spurious photothermal effects. The thermo-elastic response of isotropic and anisotropic homogeneous samples during modulated photothermal experiments are then calculated to demonstrate that interferometric measurements enable quantitative determination of some of the sample thermo-elastic parameters such as thermal diffusivity, elastic anisotropy and crystalline orientation.