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Nonlinear imaging microscopy for assessing structural and photochemical modifications upon laser removal of dammar varnish on photosensitive substrates

Varnish layers are commonly used to protect painted surfaces from atmospheric pollution, oxidation and improve the aesthetic appearance of the artwork by providing an even surface finish, brilliance and depth to the colours. However, the outer varnish layers suffer from progressive deterioration due to aging and the continuous exposure to aggressive environmental conditions, imposing the need of their removal for rectifying the optical and aesthetic properties of the painting and extend its lifetime. The removal of the surface varnish layer, without affecting the painting substrate, comprises a delicate intervention in cultural heritage (CH) conservation. The main objective of this study is to determine by nonlinear imaging microscopy (NLM) the extent of the photochemical damage that could be induced on underlying painting layers by laser removal of varnish protective coatings. This will lead to the identification of the optimal laser cleaning conditions that produce the minimum collateral damage to the painting layers. The current study is undertaken using model samples constituted by bilayers, where the top varnish layer (dammar) coats a bottom layer constituted by a doped synthetic polymer (polymetilmetacrilate, PMMA doped with POPUP) film, the latter mimicking a paint layer. The target is to determine the affected region as a function of depth of the doped polymer layer induced by laser ablation of the varnish. To this aim we use the non destructive NLM imaging modalities of third harmonic generation (THG) and multiphoton excitation fluorescence (MPEF) as novel diagnostic tools and a number of laser conditions for varnish removal, namely different ultraviolet (UV) wavelengths and pulse durations. Characterization of the samples by NLM is complemented by spectroscopic micro-Raman and laser induced fluorescence (one-photon excitation) measurements. These provide a full characterization of the lateral and in-depth chemical and morphological changes following laser removal of the varnish protective layer.

Effect of biological colonization on ceramic roofing tiles by lichens and a combined laser and biocide procedure for its removal

Biodeterioration damage is an important issue in conservation and restoration of built heritage, especially when ceramic materials are used. Biological colonization of ceramic roofing tiles by lichens is a common phenomenon. However, there are no reports to date of lichens removal from unglazed roofing tiles for conservation purposes. This paper for the first time reveals the results of a combined procedure undertaken to assess the removal of lichens on different kinds of unglazed ceramic roofing tiles by treatments based on both dual sequential laser irradiation and treatment using Acticide® CF biocide. Three species of lichens were identified: Verrucaria nigrescens, Calogaya decipiens and Pyrenodesmia teicholyta. The chemical and mineralogical composition of roofing tiles were characterized by X-ray fluorescence (XRF) spectrometry, optical polarized petrographic microscopy, and X-ray diffraction (XRD). Laser irradiation was accomplished by applying sequences of nanosecond laser pulses at two wavelengths (1064 and 266 nm). After dual sequential laser irradiation a biocide was applied. To assess the combined effect of both treatments several techniques were used, including stereo and fluorescence (FM) microscopies, scanning (SEM) and transmission (TEM) electron microscopies, and FT-Raman spectroscopy. Chemical composition of the analyzed roofing tiles was shown as a relevant factor regarding the degree of interaction between the biological colonization and the substrate, and hence, the bioweathering effect. The combined procedure has proved to be very effective in damaging and mostly collapsing the lichen thalli without altering the substrate.

Nonlinear imaging microscopy for assessing structural and photochemical modifications upon laser removal of dammar varnish on photosensitive substrates

The nonlinear optical microscopy (NLM) modalities of Multi-Photon Excited Fluorescence (MPEF) and Third Harmonic Generation (THG) have been combined in this work to characterize as a function of depth with micrometric resolution the type and extent of morphological and photochemical modifications that take place upon ultraviolet (UV) pulsed laser removal of a dammar varnish layer applied on a photosensitive substrate. The latter consists on a layer of the synthetic polymer polymethyl methacrylate doped with a photosensitizer, the aromatic compound 1,4-di[2-(5-phenyloxazolyl)] benzene, that strongly fluoresces upon UV light illumination. A number of laser conditions for partial or total elimination of the varnish coating were explored, namely different wavelengths (266, 248 and 213 nm) and pulse durations, in the nanosecond, picosecond and femtosecond ranges. Changes in the MPEF signals upon laser ablation of the outermost varnish layer successfully signpost photochemical modifications of the varnish or of the photosensitive under-layer, and their dependence with the laser ablation parameters, i.e., wavelength and pulse duration. In turn, THG signals mark the presence of layer boundaries and the reduction by laser ablation of the thickness of the varnish coating. The obtained MPEF and THG data are complemented by morphological observation by optical microscopy and measurements of laser induced fluorescence and micro-Raman spectra of the samples before and after laser ablation at the selected laser irradiation conditions. The results acquired through these nondestructive NLM imaging techniques serve to understand the phenomena that are induced upon laser ablation and to determine the best operating conditions that ensure controlled removal of the varnish with minimal morphological and chemical modifications to the under-layers. This research is of direct application to the UV pulsed laser cleaning of paintings and demonstrates the potential of NLM as a novel assessment tool for non-destructive, on line monitoring of the laser cleaning process.

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.

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

A number of techniques were employed to detect morphological and chemical changes on the irradiated surfaces. Stereomicroscopy was used to describe morphological and colour changes. Scanning electron microscopy (SEM) at low vacuum served to analyse the effects on the surface of the lichens, while SEM-BSE of the polished transversal cross sections was applied to assess effects inside the crust and in the lithic substrate. FT-Raman spectroscopy was employed to detect possible structural and chemical changes.

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Topical Imiquimod in Conjunction With Nd:YAG Laser for Tattoo Removal

ClinicalTrials.gov study NCT00638651. IPD Sharing: Not stated. Countries: 1. Publications: 1.

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Effect of biological colonization on ceramic roofing tiles by lichens and a combined laser and biocide procedure for its removal.

Biodeterioration damage is an important issue in conservation and restoration of built heritage, especially when ceramic materials are used. Biological colonization of ceramic roofing tiles by lichens is a common phenomenon. However, there are no reports to date of lichens removal from unglazed roofing tiles for conservation purposes. This paper for the first time reveals the results of a combined procedure undertaken to assess the removal of lichens on different kinds of unglazed ceramic roofing tiles by treatments based on both dual sequential laser irradiation and treatment using Acticide® CF biocide. Three species of lichens were identified: Verrucaria nigrescens, Calogaya decipiens and Pyrenodesmia teicholyta. The chemical and mineralogical composition of roofing tiles were characterized by X-ray fluorescence (XRF) spectrometry, optical polarized petrographic microscopy, and X-ray diffraction (XRD). Laser irradiation was accomplished by applying sequences of nanosecond laser pulses at two wavelengths (1064 and 266 nm). After dual sequential laser irradiation a biocide was applied. To assess the combined effect of both treatments several techniques were used, including stereo and fluorescence (FM) microscopies, scanning (SEM) and transmission (TEM) electron microscopies, and FT-Raman spectroscopy. Chemical composition of the analyzed roofing tiles was shown as a relevant factor regarding the degree of interaction between the biological colonization and the substrate, and hence, the bioweathering effect. The combined procedure has proved to be very effective in removing some lichen thalli and damaging completely the bionts in all species.

Clinical Study to Evaluate the Performance of the PicoWayTM 1064 nm/ 785 nm/ 532nm Picosecond Laser for Tattoo Removal

ClinicalTrials.gov study NCT02700932. IPD Sharing: UNDECIDED. Countries: 1. Publications: 2.

Study of the Effects of the Pulsed-dye Laser at 585nm and 595nm to Treat Post-operative Scars on Suture-removal Day

ClinicalTrials.gov study NCT00482144. IPD Sharing: Not stated. Countries: 1. Publications: 1.

Enhanced Safety Laser Hair Removal System

ClinicalTrials.gov study NCT00441948. IPD Sharing: Not stated. Countries: 1. Publications: 1.

Laser Hair Removal for Treatment of Pilonidal Disease

ClinicalTrials.gov study NCT03949140. IPD Sharing: NO. Countries: 1. Publications: 16.

Effects of Low-level Laser Therapy After Surgical Removal of Impacted Lower Third Molar

ClinicalTrials.gov study NCT04280809. IPD Sharing: NO. Countries: 1. Publications: 1.

Diode Laser as an Adjunct to Professional Mechanical Plaque Removal

ClinicalTrials.gov study NCT06719674. IPD Sharing: NO. Countries: 1. Publications: 12.

Low Laser Light Therapy After Impacted Third Molar Removal

ClinicalTrials.gov study NCT02602431. IPD Sharing: Not stated. Countries: 1. Publications: 10.

controlledIPD-YESFeb 2026View details →

A Study About Patient Satisfaction With Laser-sintered Removable Partial Dentures

ClinicalTrials.gov study NCT02769715. IPD Sharing: YES. Countries: 1. Publications: 4.

Hair Removal: Intense Pulsed Light Versus Diode Laser

ClinicalTrials.gov study NCT06179186. IPD Sharing: NO. Countries: 1. Publications: 0.

Effectiveness of Laser Hair Removal in Pilonidal Disease

ClinicalTrials.gov study NCT03276065. IPD Sharing: Not stated. Countries: 1. Publications: 2.

Efficacy of Er:YAG Laser in Removing Impacted Mandibular Third Molars

ClinicalTrials.gov study NCT07297043. IPD Sharing: UNDECIDED. Countries: 1. Publications: 0.

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Study of Picosecond and Nanosecond Q-switched Lasers for Tattoo Removal

ClinicalTrials.gov study NCT01973166. IPD Sharing: Not stated. Countries: 1. Publications: 0.

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Comparison Study of Picosecond and Nanosecond Pulse Durations Using a Q-switched Nd:YAG Laser for Tattoo Removal

ClinicalTrials.gov study NCT02244554. IPD Sharing: Not stated. Countries: 1. Publications: 0.