To improve the laser cleaning surface quality of rust layers in Q390 steel, a method of determining the optimal cleaning parameters is proposed that is based on response surface methodology and the second-generation non-dominated sorting genetic algorithm (NSGA-II). It involves constructing a mathematical model of the input variables (laser power, cleaning speed, scanning speed, and repetition frequency) and the objective values (surface oxygen content, rust layer removal rate, and surface roughness). The effects of the laser cleaning process parameters on the cleaning surface quality were analyzed in our study, and accordingly, NSGA-II was used to determine the optimal process parameters. The results indicate that the optimal process parameters are as follows: a laser power of 44.99 W, cleaning speed of 174.01 mm/min, scanning speed of 3852.03 mm/s, and repetition frequency of 116 kHz. With these parameters, the surface corrosion is effectively removed, revealing a distinct metal luster and meeting the standard for surface treatment before welding.

In this study, a pulsed laser operating at a wavelength of 1064 nm and with a pulse width of 100 ns was utilized for the removal of paint from the surface of a 2024 aluminum alloy. The experimental investigation was conducted to analyze the influence of laser parameters on the efficacy of paint layer removal from the aircraft skin\'s surface and the subsequent evolution in the microstructure of the laser-treated aluminum alloy substrate. The mechanism underlying laser cleaning was explored through simulation. The findings revealed that power density and scanning speed significantly affected the quality of cleaning. Notably, there were discernible damage thresholds and optimal cleaning parameters in repetitive frequency, with a power density of 178.25 MW/cm2, scanning speed of 500 mm/s, and repetitive frequency of 40 kHz identified as the primary optimal settings for achieving the desired cleaning effect. Thermal ablation and thermal vibration were identified as the principal mechanisms of cleaning. Moreover, laser processing induced surface dislocations and concentrated stress, accompanied by grain refinement, on the aluminum substrate.

Black silicon, which is an attractive material due to its optical properties, is prepared mainly by laser inducing in an SF6 atmosphere. Considering the effect of SF6 gas on the environment and human health, here we propose an efficient, economical, and green approach to process large-scale black silicon. In the wavelength range of 0.3-2.5 µm, the role of air could replace SF6 gas to texture black silicon by laser inducing with appropriate processing parameters. Then, to extend the working window of its excellent light-trapping status, laser-plasma shockwave cleaning was introduced to eliminate the deposition and improve the structures and morphology. The results revealed that the micro-nano structures became higher, denser, and more uniform with increasing cleaning times and deteriorating cleaning velocity, which compensated for the role of S atoms from the ambient SF6. Moreover, absorptance above 85% in the wavelength range of 0.3-15 µm was realized using our method. The effect of scanning pitch between adjacent rows on large-scale black silicon was also discussed. Our method realized the ultrahigh absorptance of large-scale black silicon fabricated in air from visible to mid-infrared, which is of significance in the field of optoelectronic devices.

The obvious advantages of laser paint removal technology make it a viable alternative to traditional paint removal methods. Infrared nanosecond laser was used to remove paint from car body. The microstructure, composition, surface roughness, hardness and ablative products of the samples were analyzed. The effect of the process combination of laser defocus distance and ambient atmosphere (ambient air, compressed air and inert atmosphere) on the substrate damage and the paint removal effectiveness was explored, and the related mechanism was discussed. Defocus not only changed the fluence of laser spot but also increased the spot diameter. The effect of defocused laser paint removal on the paint and substrate was caused by the superposition of these two factors. The results show that the laser with defocus distance of +4 mm effectively removed the paint in inert atmosphere and has the least adverse effect on the substrate. The content of C element and organic components on the substrate surface was the lowest, and its surface roughness and hardness was very close to the uncoated substrate. Focused laser paint removal in ambient air caused the most serious damage to the substrate. Its surface microhardness increased by 11 HV, and the influence depth reached 37 µm. The mechanism of laser paint removal without auxiliary gas is the superposition of laser plasma effect, laser gasification effect and thermal stress effect. In open atmosphere (compressed air and inert atmosphere), the mechanism of laser paint removal is laser gasification effect and thermal stress effect. This research can provide practical references and theoretical basis for the large-scale industrial application of low/non-damage laser paint removal technology.

The assessment of five different laser treatments in the conservation of wall paintings was devised on the basis of the surface temperature monitoring by infrared thermography (IRT), ultraviolet-induced fluorescence-visible (UV-VIS) imaging, and optical coherence tomography (OCT). A series of yttrium-aluminum-garnet (YAG) lasers were tested for removal of shellac layers from wall painting mock-ups. The mock-ups were realized as buon fresco with different mineral based pigments (earths and iron oxide) on a lime- and sand-based mortar. After the carbonatation process, all the samples were treated with shellac (5% in ethanol). The effects of neodymium (Nd):YAG, holmium (Ho):YAG, and erbium (Er):YAG laser sources, in different operative modes, on average temperature of the surface, color, and morphology were inspected with complementary sensors. The results show the necessity to adopt a combined approach in establishing safe laser operating conditions to avoid any undesired effects induced on the artefacts by the laser treatments. We demonstrate, for the first time, the performance of the Ho:YAG laser in the removal of a conservation treatment.

The microbial deterioration of cultural heritage includes physical and chemical damage as well as aesthetic alteration. With the technological advancement, a plethora of techniques for removing unwanted microorganisms have opened up new opportunities for microbiologists and conservators. This article reviews the most applied, up-to-date, and sustainable techniques developed for the control of cultural heritage microbial deterioration presenting noteworthy case studies. These techniques include chemical methods, i.e., traditional biocides and nanoparticles; physical methods, such as mechanical removal, UV irradiation, gamma radiation, laser cleaning, heat shocking, microwaves, and dry ice treatment; and biological methods, such as natural molecules with biocidal activity, enzymes, and microorganisms. The application of control systems requires the comprehension of their behavior toward the unwanted microorganisms and possible interactions with the heritage materials. This overview shows also the control methods drawbacks for the purpose of creating awareness in selecting the most suitable technique or combination of techniques.

In the present work, genetic algorithms and fuzzy logic were combined to model and optimise the shear strength of hybrid composite-polymer joints obtained by two step laser joining process. The first step of the process consists of a surface treatment (cleaning) of the carbon fibre-reinforced polymer (CFRP) laminate, by way of a 30 W nanosecond laser. This phase allows removing the first matrix layer from the CFRP and was performed under fixed process parameters condition. In the second step, a diode laser was adopted to join the CFRP to polycarbonate (PC) sheet by laser-assisted direct joining (LADJ). The experimentation was performed adopting an experimental plan developed according to the design of experiment (DOE) methodology, changing the laser power and the laser energy. In order to verify the cleaning effect, untreated laminated were also joined and tested adopting the same process conditions. Analysis of variance (ANOVA) was adopted to detect the statistical influence of the process parameters. Results showed that both the laser treatment and the process parameters strongly influence the joint performances. Then, an uncertain model based on the combination of fuzzy logic and genetic algorithms was developed and adopted to find the best process parameters\' set able to give the maximum joint strength against the lowest uncertainty level. This type of approach is especially useful to provide information about how much the precision of the model and the process varies by changing the process parameters.

Laser ablation is an accepted cleaning technology for cultural heritage stonework. Optimized laser ablation may, however, have different side effects depending on the mineralogical composition of the stone. In the case of granitic rocks, observed side effects - colour changes, fracturing or/and mineral melting - have been attributed to laser parameter interactions with the patina to be cleaned from this complex rock with a grained texture and polymineral composition. We describe the influence of the weathering degree of a granite on its response to laser irradiation, confirming that the existence of secondary minerals in the rock influences the intensity and typology of side effects. Knowledge of this influence is of special relevance to the conservation of heritage built with Western European Variscan granites, which are already slightly weathered in quarry. Two specimens of the same Variscan granite taken from the same quarry but with different colours (suggesting different weathering rates) were subjected to nanosecond (ns) Nd:YVO4 laser irradiation, working at 355 nm (UV irradiation) under different fluences. The specimens responded very differently to laser irradiation in terms of colour changes and resistance of the main minerals to laser radiation. The existence on one of the specimens of kaolinite deposits covering feldspar grains and Fe oxyhydroxides filling fissures seemed to be the reason for the different response to laser radiation. Our findings would suggest the need, during laser interventions, to take into account - in addition to texture and porosity - the degree of weathering of this particular kind of granite, widely used in the architectural and archaeological heritage of Western Europe.

A sub-aerial biofilm (SAB) developed on a granite commonly found in the built cultural heritage of the NW Iberian Peninsula was extracted with 2 different IR irradiations using an Nd:YAG laser at 1064 nm and an Er:YAG laser at 2940 nm. The methodology was based on the application of only one scan in order to evaluate the effect of the laser cleaning operated by applying different consecutive laser scanning and the suitability of these lasers as quick tools. The aim of this comparative study was twofold. The first goal was to find the most satisfactory level of extraction by comparing the results obtained by the different laser sources (IR wavelengths). The other aim was to investigate the by-effects induced by both lasers on each granite-forming mineral. Evaluations were made using stereomicroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy and scanning electron microscopy with energy-dispersive x-ray spectroscopy. The results were interpreted in terms of SAB extraction and damage induced on the granite. The results showed that the Nd:YAG laser achieved the most successful level of cleaning, because it extracted the most SAB, while causing the least amount of damage to the surfaces. Regardless of the fluence applied, the Er:YAG laser did not completely extract the SAB in only one scan; in addition, a more intense melting of biotite grains was found, producing amorphous fusion crusts and losing the distinction of the cleavage planes.

Ancient DNA from historical and subfossil wood has a great potential to provide new insights into the history of tree populations. However, its extraction and analysis have not become routine, mainly because contamination of the wood with modern plant material can complicate the verification of genetic information. Here, we used sapwood tissue from 22 subfossil pines that were growing c. 13 000 yr bp in Zurich, Switzerland. We developed and evaluated protocols to eliminate surface contamination, and we tested ancient DNA authenticity based on plastid DNA metabarcoding and the assessment of post-mortem DNA damage. A novel approach using laser irradiation coupled with bleaching and surface removal was most efficient in eliminating contaminating DNA. DNA metabarcoding confirmed which ancient DNA samples repeatedly amplified pine DNA and were free of exogenous plant taxa. Pine DNA sequences of these samples showed a high degree of cytosine to thymine mismatches, typical of post-mortem damage. Stringent decontamination of wood surfaces combined with DNA metabarcoding and assessment of post-mortem DNA damage allowed us to authenticate ancient DNA retrieved from the oldest Late Glacial pine forest. These techniques can be applied to any subfossil wood and are likely to improve the accessibility of relict wood for genome-scale ancient DNA studies.