Comparative evaluation of ultrafast laser beam interaction with the silvering in late Roman coins

This work investigates the influence of the pulse duration and the wavelength on the laser cleaning of thin silver plating layers found in late Roman coins. Comparative cleaning tests were performed using Nd:YAG (1064 nm and 532 nm - 6 ns), GaAlAs diode (780 nm - 90 ps) and Ti-Sapphire regenerative amplifier (800 nm - 100 fs) laser systems. The cleaning results on the plated areas were characterised by high resolution optical microscopy, SEM-EDX, XRF and micro-profilometry.