We have performed experiments consisting to probe a multilayer material with a pulsed laser light flux and to measure the time dependent temperature at interfaces. A real time and high gray level imagery technique gives the backscattered flux at the entrance face of the composite and the incident heat flux entering in the slab. We further present an analytical model for studying transient diffusive phenomena in a one dimensional multilayer medium submitted to periodic external conditions. This approach uses a matricial formalism and the development of the incident thermal flux on an orthogonal complete base of rectangular functions called "Walsh functions". The use of the transfer matrix formulation then leads to a eigenvalues transcendental equation. The experimental method for steady or periodic heating of the slab together with the model predictions yields the thermo-physical parameters of the multilayer medium.