Thermographic Non-Destructive Testing methods for the evaluation of materials and structures are of great interest. They are attractive because of rapid-scanning capabilities available today. The principle of photothermal methods are well known. The heat flux is applied on the sample by a laser pulse. Then, by means of a Infra-Red camera, one makes a full time record of the whole surface temperature field. There are very rich informations saved in the surface time history θ(x,t), which can be used for the reconstruction of unknown thermal conduction coefficient η(x), defects, cracks etc...