Nd:YAG laser with wavelengths from IR to UV (ω, 2ω, 3ω, 4ω) and corresponding applications in conservation of various artworks

Abstract

To cover the whole range of applications in laser cleaning of artworks, it is well known that specific wavelengths are necessary for the individual conservation problem. Recently, there is a new generation of Nd:YAG-lasers available offering frequency multiplied laser radiation from IR via VIS to UV. Using three different non-linear crystals, emission at 532 nm (2ω), 355 nm (3ω) and 266 nm (4ω) wavelengths takes place beside the fundamental wavelength 1064 nm (ω). The laser system is based on the oscillator/amplifier-principle. The non-linear crystals are placed behind the amplifier cavity. The laser system (Type “SAGA 220/10”) with maximum pulse energy of 1.5 J pulse duration of 7 ns and a maximum repetition rate of 10 Hz is equipped with an articulated arm including a hand piece. This novel system offers new fields in conservation of artworks. As far as known, we used this multi-frequency equipment for the first time in laser cleaning applications. To demonstrate the potential of this laser system for practical applications of conservation, we cleaned sandstone with black encrustation, varnish layer on a piece of wooden furniture, a painting frame with synthetic colour, a gilded iron organ and a Russian icon covered with black candle soot. As a result, it has turned out that every individual artwork mentioned above has its own specific cleaning wavelength.