Removal of co-deposited layers by excimer lasers

The JT-60 co-deposited layers with the thickness of nearly 60 μm were clearly and flatly removed by 10 pulses' KrF irradiation at the fluence of 13.3 J/cm2. The effective absorption coefficient and ablation threshold of the TFTR co-deposited layers for KrF laser were 0.4 μm-1 and 4.2 J/cm2, which were a bit larger than those of the JT-60 co-deposited layers (0.3 μm-1 and 2.3 J/cm2) for the same laser. In addition, hydrogen (tritium) was found to be released in the form of hydrogen molecules, and the combination of excimer laser and mass spectrometer or tritium monitor could be a promising technique for analyzing the depth profiles in the co-deposited layers and the substrate near the interface. Furthermore, the formation of cones on the JT-60 co-deposited layers due to local surface melting was observed at the fluence of 0.8 J/cm2 for KrF laser irradiation, whereas strong melting was determined to be the mechanism of the ablative removal of the JT-60 co-deposited layers at fluences greater than the ablation threshold of 2.3 J/cm2. (author)