  A photothermal super resolution technique is proposed for an improved
inspection of internal defects. To evaluate the potential of the laser-based
thermographic technique, an additively manufactured stainless steel specimen
with closely spaced internal cavities is used. Four different experimental
configurations in transmission, reflection, stepwise and continuous scanning
are investigated. The applied image post-processing method is based on
compressed sensing and makes use of the block sparsity from multiple
measurement events. This concerted approach of experimental measurement
strategy and numerical optimization enables the resolution of internal defects
and outperforms conventional thermographic inspection techniques.
