Effusivity depth profiling from pulsed radiometry data: comparison of different reconstruction algorithms

Pulsed photothermal radiometry has proved to be a powerful method for nondestructive, remote, and rapid characterization of inhomogenous materials, in particular, coatings evaluation and defects sizing. Another application is the characterization of gradient materials, i.e. materials whose thermal properties are continuous functions of depth. The problem is to infer the thermal profile from the transient temperature evolution alter surface pulse heating. We present here a series of inversion techniques that we developed for this purpose and we compare their performances. We focus on the important case of hardness profile retrieval in case hardened steel.