This study develops a theoretical and experimental method for atomic structure characterization. The mirage technique has been performed to prospect unknown material structures in order to diagnose eventual treatment or defect. The use of Gaussian Laser beam made photothermal deflection signal more appropriate to build-up a simple algorithm in order to investigate metal structure frequential response to a modulated heating excitation and thus identify its more probable structure. Some applications on steel quenched or annealed samples yielded interesting results such as delimitation of martensitic structure . Method is actually to be tested on differently treated material.