Fig. 1. Diagram of laser cleaning device and focal spot. (a) Diagram of laser cleaning device; (b) focal spot image of laser with wavelength of 1064 nm

Fig. 2. Preparation and analysis of marble sample. (a) Micromorphology of sample; (b) test results by X-ray fluorescence spectrometer; (c) Raman spectral component analysis

Fig. 3. Path of laser processing and outline after ablation

Fig. 4. Cross-section temperature distribution of sample after laser ablation at different wavelengths. (a) 1064 nm; (b)532 nm; (c) 355 nm

Fig. 5. Damage threshold of pollutants under picosecond laser at different wavelengths. (a) 1064 nm; (b) 532 nm; (c) 355 nm

Fig. 6. Diagram of measuring thickness of contaminated layer. (a) Map of selected area distribution; (b) micro-morphology after laser cleaning

Fig. 7. Scatter diagram of three wavelength laser energy density-monolayer ablation depth and fitted curves of blow-off model

Fig. 8. Surface morphologies of sample after cleaning by picosecond laser at different wavelengths. (a) 1064 nm; (b) 532 nm; (c) 355 nm

Fig. 9. Comparative analysis of sample surface roughness after laser cleaning at different wavelengths. (a) 1064 nm; (b) 532 nm; (c) 355 nm

Fig. 10. Elemental composition analysis of sample after laser cleaning at different wavelengths. (a) 1064 nm; (b) 532 nm; (c) 355 nm