PHOTOTHERMAL CHARACTERIZATION OF PLASMA SURFACE MODIFICATIONS

The basic concept and different detection schemes of the photothermal techniques are briefly described and main applications in plasma surface interactions are reviewed. Results of photoacoustic investigations are presented to demonstrate the depth profiling ability and the lateral resolution of the thermal wave techniques. On metal plates exposed to tokamak divertor plasmas different types of material deposition and annealing effects are identified by frequency dependent measurements. Graphite limiter tiles are found to exhibit thermal depth profiles already before plasma exposure which can be related to the surface roughness and porosity. In a last example frequency variations of the photoacoustic signals obtained from plasma-deposited amorphous hydrogen carbon and deuterium carbon films on silicon are discussed.