A theoretical model to calculate the time evolution of the surface temperature of an opaque sample containing buried cylinders or spheres, after the absorption of a short light pulse, has been developed. To do this we first calculate the temperature of the material when it is illuminated by a modulated light beam. Then, based on the analogy between the Helmholtz equation and the Laplace transform of the heat diffusion equation we obtain the Laplace transform of the solution. Finally, using the inverse Laplace transform we find the time evolution of the surface temperature heated by a short light pulse. Measurements performed by an infrared camera on a calibrated sample confirm the validity of the model.