AQTIVE - Active quantitative thermography using innovative vertical emitting lasers

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Active thermography has been a distinguished non-destructive testing method for the detection and characterization of defects and material inhomogeneities. There are two techniques that are employed almost exclusively: pulse thermography with flash-like energy input for detection of near-surface flaws and lockin thermography with periodic energy input for detection of deeper defects. Since testing is performed in a planar fashion, results are available fast and are represented as images. Quantitative reconstruction of the inside of the tested parts is extremely complex and therefore usually omitted. Alternatively, photothermal testing provides layer thickness measurements and material characterization, but only via slow point-by-point scanning. This separation into different applications is mostly due to the lack of sufficiently fast, phase stable, high-power and spectrally suitable energy sources and infrared thermography systems.The two main objectives pursued within the project are: the unification of the different thermographic and photothermal material testing and characterization techniques into one planar and quantitative measuring system, as well as the verification that this method is faster, more precise and more versatile than previous ones. Among others, we expect it to allow for testing of currently barely testable uncoated metals. The instrumental requirements for quantitative and high-precision measurements are established by integrating a novel high-power laser (vertical-cavity surface-emitting laser array) into modern infrared thermography systems. This combination yields the decisive parameters for success: Irradiance, modulation bandwidth, phase stability and spectral purity. The resulting potential is to be investigated experimentally within the project, while updated theoretical concepts are to be developed. A broad range of applications is covered by considering the different materials plastics and metals. The advantages of this approach will be verified using practical applications, such as material characterization, coating thickness measurement and fracture testing. Eventually, novel concepts for thermal wave shaping are to be developed and evaluated in order to enhance detection sensitivity.In case of success the project will help tapping the full potential of planar thermography. It will possibly provide a paradigm shift from the separated photothermal and thermography techniques to a unified, quantitative measuring and testing method that is faster and more precise.