Femtosecond pulse laser cleaning of Makrana marble

We studied femtosecond pulse lasers for cleaning Makrana marble, used in the construction of Soami Bagh Samadh, Agra, India. We investigated laser irradiation at different wavelengths (1029 nm, 515 nm, and 343 nm) and found that ultraviolet radiation had the lowest ablation threshold at 0.23 J cm⁻², followed by green at 0.34 J·cm⁻², and infrared at 1.3 J·cm⁻². Green irradiation was the most efficient, ablating marble at 0.9 mm³·(min W)^–1 at 4 J·cm⁻² compared to 0.73 mm³·(min W)^–1 at 12 J·cm⁻² for 343 and 1029 nm. We evaluated the wavelength's effect on the stone. Infrared irradiation, having a higher ablation threshold, allowed for a broader range of laser fluence for the safe removal of contaminants, without risking inducing any chemical or morphological changes to the stone, and thus was selected for cleaning. We explored the cleaning effectiveness of infrared femtosecond laser pulses on a sculpted Makrana marble covered by environmental soiling. Optical and scanning electron microscopy, optical profilometry, Raman spectroscopy, and colorimetry demonstrated that satisfactory cleaning was achieved, with the removal of the unwanted layers without causing damage or chemical alteration to the marble structure. This study demonstrates the potential of femtosecond lasers for safe and effective heritage marble cleaning.