Comparison of the characteristics HPDL, CO₂, Nd:YAG and excimer lasers for paint stripping

Three high power diode lasers (HPDLs), with 60 W fibre beam delivery, 120 W fibre beam delivery and 2.5 kW direct output, were used for the stripping of 0.3 mm thick white chlorinated rubber (CR) paint (as used in the UK nuclear industry) from concrete surfaces. Comparisons were made with two CO₂ lasers (CW and RF), an Nd:YAG laser, an excimer laser and an arc lamp. The beam absorption coefficient, ablation threshold and thermal loading have been analysed. The work has shown that although the diode lasers have lower removal rate and higher thermal loading compared with the CW CO₂ lasers, the quality of the removal is better. The mechanism of the paint stripping using the HPDL has been identified, through DTA/TGA and gas analyses, as a controlled combustion when an oxygen processing gas is used. High reflectance of the white paint material to the laser beam has been overcome by the sustained combustion wave during paint stripping once it is initiated.