Product Code: ICAL05_M603

Controlled Laser Cleaning of Artworks via Low Resolution LIBS and Linear Correlation Analysis
Authors:
Marco Lentjes, Laser Centre University of Applied Sciences Muenster; Steinfurt Germany
Johan Meijer, Engineering Technology University of Twente; Enschede The Netherlands
Klaus Dickmann, Laser Centre University of Applied Sciences Muenster; Steinfurt Germany
Presented at ICALEO 2005

Based on a fibre optic miniature spectrometer (spectral range 200-1100 nm, lambda-resolution 2 nm) we have build up a LIBS-system for online monitoring during laser cleaning of artworks. In contrast to common LIBS set-ups with ICCDs our system offers less sensitivity and lambda-resolution. This system is unsuitable for high resolved elemental identification but it is applicable for the detection of ?spectral fingerprints?.
A powerful method of comparison online spectra during laser cleaning process with reference spectra is the analysis of correlation. Based on ?Pearsons correlation? the linear relationship between the entire data sets of both spectra are classified by the correlation coefficient r: r = 1 means a correlation of 100% (complete overlapping of the spectra). In practise of laser cleaning a permanent comparison of the spectrum from the ablated layer with a reference spectrum of the layer to be preserved is necessary. Thus, online controlling of the cleaning process is enabled by permanent estimation of r. Laser removal will continue until r exceeds a predefined value subsequently the ablation process is paused. In a next step, the sample is translated and the cleaning process continues.
Successfully we have automatically cleaned glass covered with encrustation and parchment.