Pulsed thermography with laser beam homogenizing for thickness prediction of thin semi-transparent thermal barrier coatings

•Short-pulsed laser thermography is used to measure the thickness of TBCs.•A simple reconstruction algorithm based on numerical fitting is proposed.•A characteristic parameter related to the top coating thickness is identified.•The use of a laser homogenizer is critical for the robustness of the measurements. A pulsed thermography system with laser beam homogenizing is developed to measure the thickness of thermal barrier coatings (TBCs) by numerical fitting. A simplified model is proposed to avoid the complexity of deriving an analytical solution of thermal diffusion in TBC systems that include a thin semi-transparent top coating. A characteristic parameter is identified that captures the system response to fast heating by a short laser pulse and to optothermal effects due to volume heating, bulk emission and multiple reflections in the thin coating. It is demonstrated that small thickness changes can be measured when the unpainted ultra-thin TBC is thermally excited using short laser pulses with flat-top spatial profile. Experimental results show that the proposed laser thermography reconstruction method is fast and reliable when using laser beam shaping with a homogenizer.