In situ diagnostics and control of laser-induced removal of iron oxide layers

The mechanism of laser-induced removal of thermally grown iron oxide layers on pure iron has been investigated by means of in situ reflectivity measurements. The experiments were carried out by irradiating the sample with λ=584 nm, τ=6 ns (FWHM) laser pulses in a buffer borate solution after a cathodic polarisation of −1.5 V/SCE had been applied during 40 min. The removal efficiency has been studied as a function of the number of laser pulses, for several fluence values and for a few time delays after switching off the cathodic polarisation. The results demonstrate that reflectivity measurements are a suitable non-invasive in situ diagnostics tool for the assessment of the efficiency of oxide removal, that additionally provide valuable information concerning the process dynamics. Such results indicate that the electrolytic hydrogen charging of the iron oxide layer upon electrochemical treatment is the most likely mechanism responsible for the laser-induced removal process.