Cleaning of contaminated paper with the subnanosecond Nd:YAG laser pulses

Abstract

Laser cleaning and restoration of documents on the paper base offer advantages over traditional mechanical and chemical cleaning methods. In this work, the office-type paper artificially contaminated for research purposes was cleaned with subnanosecond laser pulses. Laser cleaning recovered more than 80% of the paper initial brightness observed in the visible range, whereas chemical modifications of the paper studied by the FTIR spectrometer were below the spectrometric noise level. The laser fluences above the optical breakdown threshold of the paper surface resulted in the uplift of the paper surface and thinning-out of cellulose fibres in the breakdown zone. This type of morphological modification is accompanied by the FTIR detected compositional changes of the substrate -the intensity of three CaCO3 infrared peaks decreases after laser treatment.