Active laser pyrometry and lock-in thermography for characterisation of deposited layer on TEXTOR graphite tile

Active laser pyrometry and lock-in thermography were applied for non-destructive characterisation of a deposited carbon-layer (5-40 µm thickness, different thermal contact quality) on TEXTOR graphite tile. The experimental installation comprised a pulse repetition rate laser (Nd-YAG, 1064 nm, 0.5-250 ms pulse duration, 2 Hz to 1 kHz repetition rate, 10-100 W amplitude power) and a home-made active laser pyrometry system. Active laser pyrometry was used to obtain some unknown layer properties (thermal capacity, conductivity, optical absorptivity, layer/surface thermal contact coefficient). With the developed 3D theoretical model, it was possible to calculate the heated layer temperatures with a good temporal and spatial resolution. The layer characterisation was based on the comparison of the modelling and the measured temperatures. To complete active laser pyrometry, lock-in thermography measurements of the layer/surface thermal contact coefficient were made with a new model for rapid phase shifts calculations. The obtained coefficients in both methods were comparable. Though there was no gain in the measurements accuracy, lock-in thermography has demonstrated its advantage as being much more rapid for characterisation of deposited layers of micrometric thickness.