TY - CONF A1 - Thiel, Erik A1 - Studemund, Taarna A1 - Ziegler, Mathias T1 - Spatial and temporal control of thermal waves using spatial light modulators N2 - Active thermography has been developed into a well-established non-destructive testing method and is used to detect cracks, voids, or material properties. The spatial-temporal structure of the external heating: spatially: planar (e.g., halogen lamp) or local (e.g., focused laser), and temporally: pulsed (e.g., flash lamp) or periodical (e.g., halogen lamp), has led to different testing modalities, as for instance flash and lock-in thermography. In this work, we combine a high-power laser with a spatial light modulator (SLM) allowing us to merge all degrees of freedom into a spatially and temporally controlled heat source. This approach allows us to launch a set of individually controlled and fully coherent high-energy thermal waves into the sample volume. As one possible application, we demonstrate the interference of two phase shifted thermal wave patterns in order to detect the position and depth of hidden defects, which is still a challenging task in thermographic and photothermal techniques. The patterns are positioned with a certain distance and a phase shift of pi to each other, creating an amplitude depletion zone that is centered between them. Now, when a defect is brought into the depletion zone, the destructive interference is disturbed and the defect can be recognized. This approach means that we intentionally exploit the vertical and lateral propagation directions of the thermal waves. In a more general view, controlling simultaneously control of phase and amplitude of a set of thermal waves enables us to have a defined propagation of the thermal wave field within the sample, which means that thermal waves can be controlled almost like acoustical or optical waves. However, in contrast to optical or acoustical waves, thermal waves are highly damped due to the diffusive character of the thermal heat flow and therefore limited in penetration depth in relation to the achievable spatial resolution. Nevertheless, the coherence length of thermal waves can be chosen in the mm-range for modulation frequencies below 10 Hz which is perfectly met by present SLM technology. Eventually, this offers the opportunity to transfer known technologies from wave shaping techniques to thermography methods and to exploit the possibilities of coherent thermal wave shaping. T2 - 57th Course on Photoacoustic & Photothermal Phenomena CY - Erice, Italy DA - 19.10.2016 KW - Infrared thermography KW - Thermal Wave KW - DMD PY - 2016 AN - OPUS4-37954 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -