Use of near- and mid-IR hyperspectral imaging for paint identification, as an aid for artwork authentication

In recent years various scientific practices have been adapted to the artwork analysis process and a set of techniques was found advantageous for conservation and restoration works. Apart of these applications, art market also benefits from scientific testing of artwork. Although these services are already available to support determination of the authenticity of traded pieces, they are very expensive and time consuming and therefore serve only very limited range of transactions. As a response for requirements of growing market there is a need for rapid and non-destructive methods empowering art authentication

Use of hyperspectral imaging for artwork authentication

In recent years various scientific practices have been adapted to the artwork analysis process and a set of techniques was found advantageous for conservation and restoration works. Apart of these applications, art market also benefits from scientific testing of artwork. Although these services are available to determine authenticity of traded pieces, they are very expensive and time consuming and therefore serve only very limited range of transactions. As a response for requirements of growing market there is a need for rapid and non-destructive methods empowering art authentication. Hyperspectral imaging combined with signal processing and classification techniques are proposed as a tool to enhance the identification of art forgeries. Using bespoke paintings designed for this work, a spectral library of selected pigments was established and the viability of training and the application of classification techniques based on this data was demonstrated. Developed techniques were used for the analysis of actual forged paintings held by the Berlin police, which comprised known and suspected forgeries from the infamous Beltracchi case. The analysis resulted in the identification of anachronistic paint, confirming the falsity of the artwork. Figure 1 illustrates one of analysed paintings and result of the classification, indicating Titanium White – a pigment known as anachronistic for this case

Optical parametric oscillator-based trace detection of gases in the mid-infrared region using phase-fluctuation optical heterodyne spectroscopy

Laser absorption spectroscopy utilizes a tunable infrared source, providing the necessary selectivity, to detect the characteristic fingerprint spectral absorption of an abundant gas. In a simple embodiment such as single-pass absorption, sensitivity is limited as attenuation becomes minuscule for trace level concentrations; a problem exacerbated in the midinfrared region due to significant detector noise. Sensitivity can be improved by increasing interaction between the optical field and molecular ensemble with methods such as a multiple-pass Herriot cell or resonant cavity ring-down spectroscopy but these techniques have a substantial overhead in instrumentation. An alternative approach to this problem is Phase Fluctuation Optical Heterodyne (PFLOH) spectroscopy. Here, interferometric effects are used to detect the minute heating of the sample gas when incident laser light of the appropriate wavelength is absorbed. More specifically, by placing the absorption chamber within one arm of a Mach-Zehnder interferometer, heat-induced changes in the optical path length can be detected with great sensitivity through the resulting fringe modulation. A secondary benefit is that although excitation occurs in the infrared, its effects can be detected using visible lasers and silicon detectors, thereby obviating the need for cooled, infrared detectors. We will present our results used to detect ethane using absorption in the 3.33-3.37 μm region. The Mach-Zehnder interferometer used a Helium Neon laser for the probe laser, and a broadly tunable Optical Parametric Oscillator (OPO) for spectroscopic excitation. We have demonstrated detection levels at parts per billion with further sensitivity possible by implementing several identified improvements

Use of infrared hyperspectral imaging as an aid for paint identification

Art authentication is a complicated process that often requires the extensive study of high value objects. Although a series of nondestructive techniques is already available for art scientists, new techniques, extending current possibilities, are still required. In this paper, the use of a novel mid-infrared tunable imager is proposed as an active hyperspectral imaging system for art work analysis. The system provides access to a range of wavelengths in the electromagnetic spectrum (2500–3750 nm) which are otherwise difficult to access using conventional hyperspectral imaging (HSI) equipment. The use of such a tool could be beneficial if applied to the paint classification problem and could help analysts map the diversity of pigments within a given painting. The performance of this tool is demonstrated and compared with a conventional, off-the-shelf HSI system operating in the near infrared spectral region (900–1700 nm). Various challenges associated with laser-based imaging are demonstrated and solutions to these challenges as well as the results of applying classification algorithms to datasets captured using both HSI systems are presented. While the conventional HSI system provides data in which more pigments can be accurately classified, the result of applying the proposed laser-based imaging system demonstrates the validity of this technique for application in art authentication tasks

Current challenges for high-power semiconductor disk lasers

Here we review of high-power semiconductor disk lasers including thermal management issues and new results

SOI mid-infrared silicon photonics for the 3-4 µm wavelength range

We report on the design, fabrication and characterisation of mid-infrared silicon-on-insulator strip and photonic crystal waveguides, and multi-mode interference splitters and racetrack resonators based on strip waveguides

Automatically tunable continuous-wave optical parametric oscillator for high-resolution spectroscopy and sensitive trace-gas detection

Contains fulltext : 36062pub.pdf (publisher's version ) (Closed access)We present a high-power (2.75 W), broadly tunable (2.75-3.83 mu m) continuous-wave optical parametric oscillator based on MgO-doped periodically poled lithium niobate. Automated tuning of the pump laser, etalon and crystal temperature results in a continuous wavelength coverage up to 450 cm(-1) per poling period at < 5x10(-4) cm(-1)upercript stop resolution. The versatility of the optical parametric oscillator as a coherent light source in trace-gas detection is demonstrated with photoacoustic and cavity ring-down spectroscopy. A 17-cm(-1)-wide CO2 spectrum at 2.8 mu m and multi-component gas mixtures of methane, ethane and water in human breath were measured using photoacoustics. Methane (at 3.2 mu m) and ethane (at 3.3 mu m) were detected using cavity ring-down spectroscopy with detection limits of 0.16 and 0.07 parts per billion by volume, respectively. A recording of (CH4)-C-12 and (CH4)-C-13 isotopes of methane shows the ability to detect both species simultaneously at similar sensitivities

Thermal effects in singly resonant continuous-wave optical parametric oscillators

Contains fulltext : 75693.pdf (publisher's version ) (Closed access)17 p