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The effect of wavelength and fluence on the cellulose degradation of laser-cleaned paper

The effect of a Q-switched Nd:YAG laser irradiation applied for ablative cleaning of the surface contaminants on cellulose samples and aimed on conservation of historical paper documents is investigated. The removal effectiveness of an artificial graphite contamination from model samples is investigated in dependence on the laser wavelength (532, 355 and 266 nm) and fluence (0.3 to 0.9J/cm2) and also the surface color changes are measured. Damages of cellulose fibers due to laser interaction are examined by means of the SEM technique. For irradiation at 266 nm only partial removal of the contamination and a distinct cellulose degradation, and also the yellowing of paper surface are observed. For the 355 nm wavelength and energy fluence below 0.6 J/cm2 the degradation of cellulose fibers does not occur. However, a slight yellowness of the surface is observed. The optimal cleaning wavelength of 532 nm and safe energy fluence below 0.6 J/cm2 found experimentally agree with literature.