Safe limits for the application of nonlinear optical microscopies to cultural heritage: A new method for in-situ assessment

Fovo, Alice Dal; Sanz, Mikel; Mattana, Sara; Oujja, M.; Marchetti, M. A.; Pavone, Francesco S.; Cicchi, Riccardo; Fontana, Raffaella; Castillejo, Marta

doi:10.1016/j.microc.2019.104568

Cited by 14 publications

(17 citation statements)

References 28 publications

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“…There are recent MPEF studies performed on a series of commercial acrylic paints that highlighted the dependence of the emitted fluorescence intensity on material composition and illumination conditions. This work evaluates the damage of near-infrared femtosecond pulsed lasers and establishes safe laser thresholds on a variety of painted artworks [121]. However, further studies employing different excitation wavelengths, pulse durations, and repetition rates are necessary to evaluate and determine the optimum parameters for the safe implementation of NLM on CH objects.…”

Section: Synergy Of Non-linear Techniques With Other Imaging Modalitiesmentioning

confidence: 99%

Non-Linear Microscopy: A Well-Established Technique for Biological Applications towards Serving as a Diagnostic Tool for in situ Cultural Heritage Studies

Mari

Filippidis

2020

Sustainability

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A range of sophisticated imaging techniques have been developed in recent years that can reveal the surface structure of cultural heritage objects with varying precision. In combination with various spectroscopic methods, they allow the study of the chemical composition of the object; thus, conclusions can be drawn about the origin of the object or its initial components, method, or time of creation, authenticity, mechanisms of degradation, and ways of further conservation. At present, different techniques can be applied to a wide range of cultural heritage objects, such as varnishes, paintings, archaeological objects, binding media, paper-based documents, parchments, marbles, frescoes, as well as various objects made of leather, fabric, stone, ceramics and glass, wood, or metal. One of the main needs in the study of cultural heritage (CH) is the transportability/portability of the research equipment, since many pieces under investigation cannot be moved to the laboratory, either because of their size, inseparability (for example, frescoes on walls, mural paintings in caves), or the threat of damage. In this work, we briefly overview the main optical- and laser-based methods used for the study of cultural heritage objects indicating the scope of their application, and we focus on the applications of non-linear microscopic methods for the investigation of a series of artifacts. We also discuss all the requirements for the construction of a prototype transportable non-linear optical system that will be used as a novel diagnostic tool for in situ studies of CH assets. The availability of such a transportable workstation will significantly improve the study and characterization of various types of CH objects and will constitute an extremely useful diagnostic tool for heritage scientists dealing with a variety of investigations.

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Section: Synergy Of Non-linear Techniques With Other Imaging Modalitiesmentioning

confidence: 99%

Non-Linear Microscopy: A Well-Established Technique for Biological Applications towards Serving as a Diagnostic Tool for in situ Cultural Heritage Studies

Mari

Filippidis

2020

Sustainability

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“…The second device used was a nonlinear optical microscope developed at IQFR, which allows for the point-wise collection of MPEF signals in epi-detection mode. A detailed description of this device can be found in [19,27]. Briefly, the excitation light source is a mode-locked Ti:Sapphire femtosecond laser emitting at 800 nm, releasing 70 fs pulses at a repetition rate of 80 MHz.…”

Section: Nonlinear Optical Microscopy Via Multi-photon Excitation Flumentioning

confidence: 99%

“…Briefly, the excitation light source is a mode-locked Ti:Sapphire femtosecond laser emitting at 800 nm, releasing 70 fs pulses at a repetition rate of 80 MHz. The laser beam passes through a set of two continuously variable metallic neutral density filters arranged in a serial mode (Thorlabs, NDC-50C-2M) in order to get average powers below 5 mW (which is below the damage threshold of the paints [19]). The laser beam was focused on the sample by a microscope objective lens (M Plan Apo HL 50X, Mitutoyo, NA 0.42).…”

Section: Nonlinear Optical Microscopy Via Multi-photon Excitation Flumentioning

confidence: 99%

“…The third system, a custom-made laser-scanning nonlinear optical microscope developed at INO, is described in detail elsewhere [19,35,36]. The source is an optical parametric oscillator OPO pumped by a doubled Yb-based pulsed laser with 80 MHz repetition rate (Chameleon Discovery, Coherent).…”

Section: Nonlinear Optical Microscopy Via Multi-photon Excitation Flumentioning

confidence: 99%

“…As regards nonlinear absorption processes (MPEF), safe measurement conditions can be achieved by keeping the laser power within specific limits that are related to the optical properties and chemical composition of each material. More specifically, by monitoring the photo-damage induced by MPEF upon repetitive irradiation on a series of modern acrylic painted samples, it was highlighted that the photon dose used for irradiation is a crucial parameter for preventing damage [19]. The power threshold-i.e., the laser power at which the fluorescence intensity starts to decrease after consecutive irradiations-sets the limit for safe cross-sectional imaging of paint layers by MPEF, while still gathering enough nonlinear optical signals at a suitable signal-to-noise ratio.…”

Section: Introductionmentioning

confidence: 99%

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In-Depth Analysis of Egg-Tempera Paint Layers by Multiphoton Excitation Fluorescence Microscopy

et al. 2020

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The non-invasive depth-resolved imaging of pictorial layers in paintings by means of linear optical techniques represents a challenge in the field of Cultural Heritage (CH). The presence of opaque and/or highly-scattering materials may obstruct the penetration of the radiation probe, thus impeding the visualization of the stratigraphy of paintings. Nonlinear Optical Microscopy (NLOM), which makes use of tightly-focused femtosecond pulsed lasers as illumination sources, is an emerging technique for the analysis of painted objects enabling micrometric three-dimensional (3D) resolution with good penetration capability in semi-transparent materials. In this work, we evaluated the potential of NLOM, specifically in the modality of Multi-Photon Excitation Fluorescence (MPEF), to probe the stratigraphy of egg-tempera mock-up paintings. A multi-analytical non-invasive approach, involving ultraviolet-visible-near infrared (UV-Vis-NIR) Fiber Optics Reflectance Spectroscopy, Vis-NIR photoluminescence, and Laser Induced Fluorescence, yielded key-information for the characterization of the constituting materials and for the interpretation of the nonlinear results. Furthermore, the use of three nonlinear optical systems allowed evaluation of the response of the analyzed paints to different excitation wavelengths and photon doses, which proved useful for the definition of the most suitable measurement conditions. The micrometric thickness of the paint layers, which was not measurable by means of Optical Coherence Tomography (OCT), was instead assessed by MPEF, thus demonstrating the effectiveness of this nonlinear modality in probing highly-scattering media, while ensuring the minimal photochemical disturbance to the examined materials.

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Emerging photonic technologies for cultural heritage studies: the examples of non-linear optical microscopy and photoacoustic imaging

et al. 2022

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The availability of non-invasive technologies, which can be used separately or in combination for obtaining chemical composition data and structural information of Cultural Heritage (CH) materials, is of prime importance for improving the understanding the environmental or ageing impact on monuments and artefacts and defining optimal strategies for their conservation. This paper overviews and assesses the potential of two emerging photonic technologies, the Non-linear Optical Microscopy (NLOM) and Photoacoustic (PA) imaging modalities, for a variety of diagnostic applications in preservation science. These techniques, which are well-established in biomedical research, during the last few years have been also investigated as non-invasive tools for the in-depth, high-resolution analysis of various CH objects, including paintings, documents and murals. We discuss on the applicability of these diagnostic optical methods to obtain precise stratigraphic information in artefacts, evaluating additionally the presence and the extent of potential morphological or chemical changes in several CH materials due to ageing. Furthermore, we demonstrate that the contrast complementarity of NLOM and PA imaging provides invaluable insights into the structural integrity of an artwork, which can be subsequently utilized for the early and accurate detection of depth degradation effects.

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Safe limits for the application of nonlinear optical microscopies to cultural heritage: A new method for in-situ assessment

Cited by 14 publications

References 28 publications

Non-Linear Microscopy: A Well-Established Technique for Biological Applications towards Serving as a Diagnostic Tool for in situ Cultural Heritage Studies

Non-Linear Microscopy: A Well-Established Technique for Biological Applications towards Serving as a Diagnostic Tool for in situ Cultural Heritage Studies

In-Depth Analysis of Egg-Tempera Paint Layers by Multiphoton Excitation Fluorescence Microscopy

Emerging photonic technologies for cultural heritage studies: the examples of non-linear optical microscopy and photoacoustic imaging

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