A short pulse, free running, Nd:YAG laser for the cleaning of stone cultural heritage

This paper presents a Nd:YAG laser operating in free running (FR) regime, with a pulse duration (20 mus) shorter than conventional systems (> 200 mus), mainly developed for applications in laser cleaning of stones, especially for the restoration of cultural heritage. The system was also optimized to achieve high energy and low divergence, for easy coupling with optical fibers. The unusual pulse temporal regime induces a spiky behavior of the laser output which could also help in the application. Details on the technologies for the flashlamps power supplies, including the discharge circuits needed to achieve the short pulses, are given. Application trials on artworks and artificial samples are also discussed. Results show that the intermediate pulse duration avoids the mechanical damage induced by the photomechanical effect of Q-switch lasers and the thermal damage, as superficial melting, usually induced by long pulse FR lasers. (C) 2002 Elsevier Science Ltd. All rights reserved.