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The complex composition of cultural heritage (CH) items presents significant challenges in assessing their condition and predicting potential risks of material degradation. Typically employed diagnostic optical methods are inevitably limited by light scattering, thus restricting in-depth investigations of objects with complex structural and optical properties. To address this issue, we introduce a novel reflection-mode optoacoustic (OA) diagnostic system for non-contact and non-invasive measurements of CH, placing emphasis on the detection of ageing-related modifications in artistic media such as paints. In this direction, the sensitivity of OA measurements was proven to be up to two orders of magnitude higher than conventional absorption spectroscopy assessments. Furthermore, we have evaluated the in-depth imaging capabilities of the developed OA system, demonstrating that it can offer superior contrast levels of sketches beneath opaque paint layers compared to standard near-infrared diagnostic techniques. The current OA imaging technology may advance state-of-the-art diagnostic capabilities in CH preservation by delivering unprecedented depth-to-resolution ratios combined with exceptional optical absorption sensitivity in a non-invasive manner. These features are crucial for the early detection of material degradation and the comprehensive analysis of CH objects, facilitating the development of optimal conservation strategies to prolong their lifespan and preserve their aesthetic value. [ABSTRACT FROM AUTHOR]

In the context of this work, a prototype hybrid photoacoustic (PA) and optical system for the on-line monitoring of laser cleaning procedures is presented. The developed apparatus has enabled the detection of MHz frequency range acoustic waves generated during the laser ablation process. The intrinsically generated PA signals combined with high resolution optical images provide the opportunity to follow the cleaning process accurately and in real time. Technical mock-ups have been used to demonstrate the potential of this novel technique with emphasis given to applications that refer to the restoration of Cultural Heritage (CH) surfaces. Towards this purpose, the real time monitoring of the laser assisted removal of unwanted encrustation from stonework has been achieved using IR and UV wavelengths. This novel approach has allowed for the precise determination of the critical number of laser pulses required for the elimination of the encrustation layer, while highlighting the dominant ablation mechanisms according to the irradiation wavelength. The promising results obtained using the prototype hybrid PA and optical system can open up new perspectives in the monitoring of laser cleaning interventions, promoting an improved restoration outcome.

The study, preservation and restoration of cultural heritage materials and objects are crucial for obtaining important historical information, maintaining their aesthetic appeal or understanding early technologies. The unique, highly diverse character of cultural heritage items impose the need for rigorous scientific approaches, often incorporating non-invasive, mobile or remote technologies and the valorisation of objects and preservation methodologies. Here, we overview the fundamental aspects in the use of lasers for the analysis and restoration of artworks. For the former purpose, emphasis is placed on the use of Raman and Laser-Induced-Breakdown spectroscopies, both of which have been of increasing importance in the field of Cultural Heritage. The use of lasers for the restoration of artworks, in particular of painted artworks and parchments are described. Studies on model polymeric systems, as well as realistic artefacts, have permitted detailed assessment of the mechanisms and of the effects of the procedure. Finally, we provide an assessment of the potential of new laser-based technologies and techniques for the purpose of conservation/restoration of cultural objects. Keywords: lasers; preservation of cultural heritage

Evidence is provided for the line-narrowing from the ultraviolet (UV) photoexcited open form of the photochromic molecule, indolinospiropyran (1',3'-dihydro-1',3',3'-trimethyl-6-nitrospiro [2H-1-benzopyran-2,2'-(2H)-indole]) in the solid state. The results have paved the way for the realization of hybrid devices based on the coupling between photochromic behavior and stimulated emission from conjugated molecules, such as laser optical memories and lasers gated by optical molecular switches.

Polarization-dependent second harmonic generation (PSHG) microscopy is used as an innovative, high-resolution, non-destructive, and label-free diagnostic imaging tool to elucidate biological issues with high significance. In the present study, information on the structure and directionality of collagen fibers in equine pericardium tissue was collected using PSHG imaging measurements. In an effort to acquire precise results, three different mathematical models (cylindrical, trigonal, and general) were applied to the analysis of the recorded PSHG datasets. A factor called the "ratio parameter" was calculated to provide quantitative information. The implementation of the trigonal symmetry model to the recorded data led to the extraction of improved results compared with the application of the widely used cylindrical symmetry model. The best outcome was achieved through the application of the general model that does not include any kind of symmetry for the data processing. Our findings suggest that the trigonal symmetry model is preferable for the analysis of the PSHG datasets acquired from the collagenous tissues compared with the cylindrical model approach although an increased computational time is required. [ABSTRACT FROM AUTHOR]

The development of label-free non-destructive techniques to be used as diagnostic tools in cancer research is of great importance for improving the quality of life for millions of patients. Previous studies have demonstrated that Third Harmonic Generation (THG) imaging could differentiate malignant from benign unlabeled human breast biopsies and distinguish the different grades of cancer. Towards the application of such technologies to clinic, in the present report, a deep learning technique was applied to THG images recorded from breast cancer tissues of grades 0, I, II, and III. By the implementation of a convolutional neural network (CNN) model, the differentiation of malignant from benign breast tissue samples and the discrimination of the different grades of cancer in a fast and accurate way were achieved. The obtained results provide a step ahead towards the use of optical diagnostic tools in conjunction with the CNN image classifier for the reliable and rapid malignancy diagnosis in clinic. [ABSTRACT FROM AUTHOR]

Diffractive optics fabrication is performed by two complementary processing methods that rely on the photoablation of materials by ultrashort UV laser pulses. The spatially selective ablation of materials permits the direct microetching of high-quality surface-relief patterns. In addition, the direct, spatially selective transfer of the ablated material onto planar and nonplanar receiving substrates provides a complementary microprinting operation. The radiation from the ultrashort pulsed excimer laser results in superior quality at relatively low-energy density levels, owing to the short absorption length and minimal thermal-diffusion effects. Computer-generated holographic structures are produced by both modes of operation. Submicrometer features, including Bragg-type structures, are microprinted onto planar and high-curvature optical-fiber surfaces, demonstrating the unique ability of the schemes for complex microstructure and potentially nanostructure development.

The in‐vivo elucidation of the molecular mechanisms underlying muscles dysfunction due to aging via non‐invasive label free imaging techniques is an important issue with high biological significance. In this study, polarization‐dependent second‐harmonic generation (PSHG) was used to evaluate structural alterations in the striated muscles during Caenorhabditis elegans lifespan. Young and old wild‐type animals were irradiated. The obtained results showed that it was not feasible to detect differences in the structure of myosin that could be correlated with the aging of the worms, via the implementation of the classical, widely used, cylindrical symmetry model and the calculation of the SHG anisotropy values. A trigonal symmetry model improved the extracted results; however, the best outcome was originated from the application of a general model. Myosin structural modifications were monitored via the estimation of the difference in spectral phases derived from discrete Fourier transform analysis. Age classification of the nematodes was achieved by employing both models, proving the usefulness of the usage of PSHG microscopy as a potential diagnostic tool for the investigation of muscle diseases. [ABSTRACT FROM AUTHOR]

Early-arriving photons of 100-fs laser pulses transmitted through highly scattering media have been detected by a streak camera. Because of their partial spatial coherence, they are affected by diffraction from small hidden discontinuities. The experimental data of the patterns are analyzed with Fresnel diffraction theory and then corrected accordingly. Submillimeter hidden objects were scanned and imaged. Diffraction correction resulted in a significantly improved contrast in the hidden object's image. Key words: Ultrafast transillumination, diffraction correction, image-contrast improvement.

Nonlinear optical imaging techniques have been widely used to reveal biological structures for accurate diagnosis at the cellular as well as the tissue level. In the present study, polarization‐dependent second‐harmonic generation (PSHG) was used to determine collagen orientation in breast cancer biopsy tissues (grades 0, I, II and III). The obtained data were processed using fast Fourier transform (FFT) analysis, while second‐harmonic generation (SHG) anisotropy and the "ratio parameter" values were also calculated. Such measurements were shown to be able to distinguish collagen structure modifications in different cancer grades tested. The analysis presented herein suggests that PSHG imaging could provide a quantitative evaluation of the tumor state and the distinction of malignant from benign breast tissues. The obtained results also allowed the development of a biophysical model, which can explain the aforementioned differentiations and is in agreement with the simulations relating the SHG anisotropy values with the mechanical tension applied to the collagen during cancer progression. The current approach could be a step forward for the development of new, nondestructive, label free optical diagnostic tools for cancer reducing the need of recalls and unnecessary biopsies, while potentially improving cancer detection rates. [ABSTRACT FROM AUTHOR]

We report on picosecond UV-laser processing of hexagonal boron nitride (BN) at moderately high pressures above 500 bar. The main effect is specific to the ambient gas and laser pulse duration in the ablation regime: when samples are irradiated by 5 or 0.45 ps laser pulses in nitrogen gas environment, multiple nucleation of a new crystalline product-BN nanorods-takes place. This process is triggered on structural defects, which number density strongly decreases upon recrystallization. Nonlinear photon absorption by adsorbed nitrogen molecules is suggested to mediate the nucleation growth. High pressure is responsible for the confinement and strong backscattering of ablation products. A strong surface structuring also appears at longer 150 ps laser irradiation in similar experimental conditions. However, the transformed product in this case is amorphous strongly contaminated by boron suboxides BxOy. [ABSTRACT FROM AUTHOR]

We performed a comparative study of the plasma generated from AlN targets under sub-ps vs ns UV (λ = 248 nm) excimer laser pulses. Optical emission and time-of-flight spectra recorded in cases of samples irradiated with ns laser pulses showed the presence of Al lines, which became prevalent after the first laser pulse was incident on the target. These observations are congruent with the metallization of AlN targets inside each crater under multipulse ns laser action at laser fluences above the ablation threshold, observed by visual inspection and optical microscopy. Metallization was not observed when working with sub-ps laser pulses. Moreover, our studies confirmed the predominant presence of AlN positive molecular ions in the plasma generated in front of AlN targets submitted to sub-ps multipulse laser irradiation. The optical emission data are in good agreement with time-of-flight mass analysis. We emphasize that all investigations support the experimental evidence reported by György et al. [E. György et al., J. Appl. Phys. 90, 456 (2001)], according to which thin films obtained by pulsed laser deposition with ns laser pulses contain a significant amount of metallic Al, while only AlN is detected in films obtained with sub-ps laser pulses. Measurements of the velocity and kinetic energy distributions of AlN[sup +] indicate that in the case of ns-laser ablation the ions are emitted with thermal energy, while in the case of sub-ps-laser ablation a bimodal distribution exists and has thermal (1 eV) and hyperthermal (10 eV) energy components. This points to different plasma formation mechanisms for the two cases. [ABSTRACT FROM AUTHOR]

We report a comparative study of the ultraviolet laser ablation of graphite, in vacuum, using nanosecond (34 ns), picosecond (5 ps), and femtosecond (450 fs) pulses of 248 nm radiation, focusing on the plume characteristics as revealed by wavelength, time- and spatially resolved optical emission spectroscopy. Nanosecond pulsed ablation gives a distinctively different optical emission spectrum from that observed with the two shorter pulse durations. Emissions attributable to electronically excited C[sup *], C[sup +*] and C[sub 2][sup *] fragments are identified in the former, while the spectra obtained when using the shorter duration, higher intensity pulses contain additional lines attributable to C[sup 2+*] species but none of the C[sup *] emission lines. As before [Claeyssens et al., J. Appl. Phys. 89, 697 (2001)], we consider that each atomic emission is a step in the radiative cascade that follows when an electron recombines with a C[sup n+] species (where n is one charge state higher than that of the observed emitter) formed in the original ablation process. Broadband visible radiation attributable to blackbody emission from larger particulates is also observed following ablation with any of the three laser pulse durations. Time gated imaging studies allow estimation of the velocity distributions of various of these emitting species within the plume, and their variation with incident laser fluence and/or intensity. The deduced multicomponent structure of the plume emission following excitation with short duration laser pulses is rationalized in terms of contributions from both nonthermal and thermal mechanisms for material ejection from the target. Use of longer duration (nanosecond) laser pulses offers the opportunity for additional laser-plume interactions, which we suggest are responsible for much of the observed emission in the nanosecond pulsed laser ablation of graphite. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The modifications induced in haloaromatic, ArX (Ar, Nap, Phen, and An; X = Br and I), dopants dispersed within poly(methyl methacrylate) (PMMA) upon UV irradiation are examined. The results are well accounted for within a thermal model of the laser interaction with PMMA and the factors that controls the reactivity in the UV ablation of polymer substrates are illustrated.

The (2+1) multiphoton ionization (MPI) spectrum of jet-cooled CS2 has been recorded in the range 345–370 nm, corresponding to a two-photon frequency between 54 000 and 58 000 cm-1. The origin bands of the ...2π3g4sσg 1Πg and 3Πg←X 1Σ+g Rydberg transitions have been observed at 351.04 and 355.15 nm (vacuum 56 974 and 56 315 cm-1), respectively. A third, broader and stronger, band is observed at ∼365 nm corresponding to a two-photon transition at ∼54 700 cm-1, which is suggested to belong to the valence 5σu3πu 1Πg state. The position of the two-photon band at 351 nm establishes it as the one-photon electric-dipole forbidden origin of the 800 cm-1 progression observed in the ultraviolet absorption spectrum. The first-photon frequency of this transition falls at a level corresponding to the a 3A2 valence state, so that the (2+1) MPI spectrum is supplemented by numerous transitions associated with the (1+2) MPI spectrum of the 3A2←X 1Σ+g transition. [ABSTRACT FROM AUTHOR]

Positively charged micron sized clusters are efficiently produced following irradiation of thiophenol vapor at 248 nm by a single KrF laser pulse of 30 ns duration. The production mechanism has been studied by examining the effect of N2, Ar, and He as diffusion media in mixtures with thiophenol, and by varying the laser pulse energy and excitation wavelength. A qualitative summary of possible mechanisms that may be responsible for the experimental results is presented providing a framework for understanding the observed cluster growth. The measurements indicate an optimum set of parameters for growth of large clusters and also show that the cluster charge can be controlled by selection of the buffer gas mixture. [ABSTRACT FROM AUTHOR]

This work reports the fabrication of Nb/Pb structures with an application as photocathode devices. The use of relatively low energy densities for the ablation of Nb with ultrashort pulses favors the reduction of droplets during the growth of the film. However, the use of laser fluences in this ablation regime results in a consequent reduction in the average deposition rate. On the other hand, despite the low deposition rate, the films present a superior adherence to the substrate and an excellent coverage of the irregular substrate surface, avoiding the appearance of voids or discontinuities on the film surface. Moreover, the low energy densities used for the ablation favor the growth of nanocrystalline films with a similar crystalline structure to the bulk material. Therefore, the use of low ablation energy densities with ultrashort pulses for the deposition of the Nb thin films allows the growth of very adherent and nanocrystalline films with adequate properties for the fabrication of Nb/Pb structures to be included in superconducting radiofrequency cavities. [ABSTRACT FROM AUTHOR]

The application of multispectral imaging to discriminate myelinated and demyelinated areas of neural tissue is herein presented. The method is applied through a custom-made, multispectral imaging monochromator, coupled to a commercially availablemicroscope. In the present work, a series of spinal cord sections were analysed derived from mice with experimental autoimmune encephalomyelitis (EAE), an experimentalmodel widely used to study multiple sclerosis (MS). The multispectral microscope allows imaging of local areas with loss of myelin without the need of tissue labelling. Imaging with the aforementioned method and system is compared in a parallel way with conventional methods (wide-field and confocal fluorescencemicroscopies). The diagnostic sensitivity of ourmethod is 90.4% relative to the 'gold standard' method of immunofluorescence microscopy. The presented method offers a new platform for the possible future development of an in vivo, real-time, non-invasive, rapid imaging diagnostic tool of spinal cordmyelin loss-derived pathologies. [ABSTRACT FROM AUTHOR]

ABSTRACT The elucidation of the molecular mechanisms that lead to the development of metabolic syndrome, a complex of pathological conditions including type-2 diabetes, hypertension, and cardiovascular diseases, is an important issue with high biological significance and requires accurate methods capable of monitoring lipid storage distribution and dynamics in vivo. In this study, the nonlinear phenomena of second and third harmonic generation (SHG, THG) have been employed simultaneously as label-free, nondestructive diagnostic techniques, for the monitoring and the complementary three-dimensional (3D) imaging and analysis of the muscular areas and the lipid content localization. THG microscopy was used as a quantitative tool in order to record the accumulation of lipids in nonadipose tissues in the pharyngeal muscles of 18 Caenorhabditis elegans (C. elegans) specimens, while the SHG imaging provided the detailed anatomical information about the structure of the muscles. The ectopic accumulation of fat on the pharyngeal muscles increases in wild-type (N2) C. elegans between 1 and 9 days of adulthood. This suggests a correlation of ectopic fat accumulation with the process of aging. Our results can contribute to the unraveling of the link between the deposition of ectopic fat and aging, but mainly to the validation of SHG and THG microscopy modalities as new, noninvasive tools to localize and quantify selectively lipid formation and distribution. Microsc. Res. Tech. 78:523-528, 2015. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Elucidation of the molecular mechanisms regulating lipid storage and metabolism is essential for mitigating excess adiposity and obesity, which has been associated with increased prevalence of severe pathological conditions such as cardiovascular disorders and type II diabetes, worldwide. However, imaging fatty acid distribution and dynamics in vivo, at the cellular or organismal level is challenging. We developed a label-free method for visualizing lipid depositions in vivo, based on third harmonic generation (THG) microscopy. THG imaging requires a single pulsed-laser light source, alleviating the technical challenges of implementing coherent anti-Stokes Raman scattering spectroscopy (CARS) to detect fat stores in living cells. We demonstrate that THG can be used to efficiently and reliably visualize lipid droplets in Caenorhabditis elegans. Thus, THG microscopy offers a versatile alternative to fluorescence and dye-based approaches for lipid biology research. [ABSTRACT FROM AUTHOR]

The first reduction methodology, compatible with flexible, temperature-sensitive substrates, for the production of reduced spin-coated graphene oxide (GO) electrodes is reported. It is based on the use of a laser beam for the in situ, non-thermal, reduction of spin-coated GO films on flexible substrates over a large area. The photoreduction process is one-step, facile, and is rapidly carried out at room temperature in air without affecting the integrity of the graphene lattice or the flexibility of the underlying substrate. Conductive graphene films with a sheet resistance of as low as 700 Ω sq−1 and transmittance of 44% can be obtained, much higher than can be achieved for flexible layers reduced by chemical means. As a proof of concept of our technique, laser-reduced GO (LrGO) films are utilized as transparent electrodes in flexible, bulk heterojunction, organic photovoltaic (OPV) devices, replacing the traditional ITO. The devices displayed a power-conversion efficiency of 1.1%, which is the highest reported so far for OPV device incorporating reduced GO as the transparent electrode. The in situ non-thermal photoreduction of spin-coated GO films creates a new way to produce flexible functional graphene electrodes for a variety of electronic applications in a process that carries substantial promise for industrial implementation. [ABSTRACT FROM AUTHOR]

Engineering artificial scaffolds that enhance cell adhesion and growth in three dimensions is essential to successful bone tissue engineering. However, the fabrication of three-dimensional (3D) tissue scaffolds exhibiting complex micro- and nano-features still remains a challenge. Few materials can be structured in three dimensions, and even those have not been characterized for their mechanical and biological properties. In this study, we investigate the suitability of three novel materials of different chemical compositions in bone tissue regeneration: a hybrid material consisting of methacryloxypropyl trimethoxysilane and zirconium propoxide, a hybrid organic-inorganic material of the above containing 50 mole% 2-(dimethylamino)ethyl methacrylate (DMAEMA) and a pure organic material based on polyDMAEMA. More specifically, we study the mechanical properties of the aforementioned materials and evaluate the biological response of pre-osteoblastic cells on them. We also highlight the use of a 3D scaffolding technology, Direct femtosecond Laser Writing (DLW), to fabricate complex structures. Our results show that, while all three investigated materials could potentially be used as biomaterials in tissue engineering, the 50% DMAEMA composite exhibits the best mechanical properties for structure fabrication with DLW and strong biological response. © 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2013. [ABSTRACT FROM AUTHOR]

This paper is a review of our recent work on electrowetting properties of devices based on silicon (Si) and metal oxide (MO) electrodes. In particular, the electrowetting-on-dielectric (EWOD) properties of three-dimensional (3D) structured Si and MO electrodes are investigated and compared with those of planar ones. It is shown that the EWOD properties of these materials can be advantageously controlled by altering their geometry and/or their surface chemistry. Ultrafast laser irradiation was used in order to produce 3D superhydrophobic Si electrodes exhibiting double-scale roughness, in the micro- and nano-scales. The metal oxide electrodes were fabricated by depositing hydrophobic ZnO or TÍO2 nanostructures onto the laser textured substrates using Pulsed Laser Deposition (PLD). The EWOD induced contact angle changes on the 3D structured surfaces show reversible or non-reversible behaviour depending on the geometry of the surface structures. Reversibility is observed when the double-scale roughness becomes more pronounced. [ABSTRACT FROM AUTHOR]

We present our research into the fabrication of fully three-dimensional metallic nanostructures using diffusion-assisted direct laser writing, a technique which employs quencher diffusion to fabricate structures with resolution beyond the diffraction limit.We have made dielectric 3D nanostructures by multiphoton polymerization using a metal-binding organic-inorganic hybrid material, and we covered them with silver using selective electroless plating. We have used this method to make spirals and woodpiles with 600nm intralayer periodicity. The resulting photonic nanostructures have a smooth metallic surface and exhibit well-defined diffraction spectra, indicating good fabrication quality and internal periodicity. In addition, we have made dielectric woodpile structures decorated with gold nanoparticles. Our results show that diffusion-assisted direct laser writing and selective electroless plating can be combined to form a viable route for the fabrication of 3D dielectric and metallic photonic nanostructures. [ABSTRACT FROM AUTHOR]

The applicability of a femtosecond KrF laser in absorbing filmassisted, laser-induced forward transfer of living cells was studied. The absorbing materials were 50-nm-thick metal films and biomaterials (gelatine, Matrigel, each 50 μm thick, and polyhydroxybutyrate, 2 μm). The used cell types were human neuroblastoma, chronic myeloid leukemia, and osteogenic sarcoma cell lines, and primary astroglial rat cells. Pulses of a 500-fs KrF excimer laser focused onto the absorbing layer in a 250-μm diameter spot with 225 mJ/cm2 fluence were used to transfer the cells to the acceptor plate placed at 0.6 mm distance, which was a glass slide either pure or covered with biomaterials. While the low-absorptivity biomaterial absorbing layers proved to be ineffective in transfer of cells, when applied on the surface of acceptor plate, the wet gelatine and Matrigel layers successfully ameliorated the impact of the cells, which otherwise did not survive the arrival onto a hard surface. The best shortand long-term survival rate was between 65% and 70% for neuroblastoma and astroglial cells. The long-term survival of the transferred osteosarcoma cells was low, while the myeloid leukemia cells did not tolerate the procedure under the applied experimental conditions. [ABSTRACT FROM AUTHOR]