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Within the scope of a DIN INS project, a flash thermography round robin test that evaluates reliability, comparability, and efficiency of different testing situations was organized. The results give information about the detectability of defects, e.g. depending on their size and depth, the evaluation methods and the materials used. Besides, the influences of equipment and parameters used by the participants on the results were analysed. All of the quantitative results as well as the feedback given by the participants will be presented in a DIN committee in order to contribute to a flash thermography standard.
The irradiation of solids with high-intensity laser pulses can excite materials into extreme conditions, which then return to equilibrium via various structural and topographical relaxation mechanisms. Thus, ultrafast laser processing can manifest in various morphological surface transformations, ranging from direct contour shaping to large-area-surface functionalization through the generation of self-organized nano- and microstructures. The interaction mechanisms between semiconductors and metals with ultrashort laser pulses have been extensively studied using femtosecond laser sources, generating a general understanding of the main interaction mechanisms present during the processing of those materials. In the specific case of nanometer-scaled laser-induced periodic surface structures (LIPSS), however, the general explanation that fits all the experimental outcomes is still to be completed. The most accepted explanation consists in the interference of the incoming laser pulse with light scattered at the rough surface, e.g. via surface plasmon polaritons. Such scattering and interference effects generate a spatially modulated pattern of the absorbed optical energy featuring maxima and minima with periods very close to the laser irradiation wavelength, λ. One general criterion that allows to classify LIPSS in terms of their spatial periodicity (Λ) for normally incident radiation is the following: low spatial frequency for Λ≈λ, and high spatial frequency for Λ≪λ. In this way, the right combination of irradiation parameters (laser fluence, number of pulses per spot area unit and repetition rate) could be used to cover a wide size range that can ultimately be exploited for different applications in optics, biology, fluidics and tribology among others.