Influence of wavelength on the laser removal of lichens colonizing heritage stone-Associated dataset

Stone samples from Alpedrete quarry front, Madrid (Spain), which were used to construct heritage buildings and monuments in the Central area of Spain, and from Valonsadero Church (Spain), presenting different types of biological crusts were investigated in order to find the conditions for efficient laser treatment. Samples presenting superficial areas colonized by 6 different lichens: Protoparmeliopsis volcana and muralis (foliose), Aspicilia vidrescensa and contorta, Candelariella vitelina and Rhizocarpon disporum (crustose) were selected for laser treatment.

In order to determine the best laser irradiation conditions UV-Visible absorption spectroscopy was performed from ethanol diluted bioderioration crust of each sample and ablation threshold was found for each stone substrate. A comparative study was carried out on the mentioned samples with infrared, ultraviolet and sequences of both nanosecond laser pulses using the fundamental (1064 nm), 3rd (355 nm) and 4th (266 nm) harmonic output of a Q-switched Nd:YAG laser system (pulse duration 17 ns, repetition rate 1-10 Hz) at fluences just below umbral threshold.