Laser Cleaning Monitored by a Spectroscopic Technique — Experimental Data on The Gotlandic Sandstone Case

Abstract

The LIPS spectra obtained for the historical samples of Gotlandic sandstone (XVI c) under pulsed laser irradiation at 355 and 1064nm are analysed and applied for monitoring of the surface cleaning process. The spectra are recorded in the range 370 - 760 nm upon successive cleaning pulses and depend strongly on the laser wavelength and dose applied. Peaks assigned to Ca I, Ca II, AI I, Ba I, Li I and Mg I (crust) and to Si I, Si II and Al II (stone) are observed. An exponential decay of the Ca I, Ca II and Al I peak intensities accompanies the cleaning progress. The short term colour changes of the sandstone surface due to laser irradiation are not revealed by colorimetric measurements.