Low Resolution LIBS for Online-Monitoring During Laser Cleaning Based on Correlation with Reference Spectra

Abstract

Based on a commercial miniature spectrometer, we have built a LIBSsystem for online monitoring and controlling during laser cleaning of artworks. In contrast to common LIBS set-ups with ICCDs, our system offers less sensitivity and λ-resolution. This system is unsuitable for high resolution 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 “Pearson’s correlation”, the linear relationship between entire data sets of both spectra are classified by the correlation coefficient r . 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 monitoring of the cleaning process is enabled by permanent estimation of r . In case of closed-loop laser cleaning the ablation will continue until r exceeds a predefined value and subsequently the ablation process is automatically stopped.