Advances in multispectral and hyperspectral imaging for archaeology and art conservation

Multispectral imaging has been applied to the field of art conservation and art history since the early 1990s. It is attractive as a noninvasive imaging technique because it is fast and hence capable of imaging large areas of an object giving both spatial and spectral information. This paper gives an overview of the different instrumental designs, image processing techniques and various applications of multispectral and hyperspectral imaging to art conservation, art history and archaeology. Recent advances in the development of remote and versatile multispectral and hyperspectral imaging as well as techniques in pigment identification will be presented. Future prospects including combination of spectral imaging with other noninvasive imaging and analytical techniques will be discussed

Macroscale multimodal imaging reveals ancient painting production technology and the vogue in Greco-Roman Egypt.

Macroscale multimodal chemical imaging combining hyperspectral diffuse reflectance (400-2500 nm), luminescence (400-1000 nm), and X-ray fluorescence (XRF, 2 to 25 keV) data, is uniquely equipped for noninvasive characterization of heterogeneous complex systems such as paintings. Here we present the first application of multimodal chemical imaging to analyze the production technology of an 1,800-year-old painting and one of the oldest surviving encaustic ("burned in") paintings in the world. Co-registration of the data cubes from these three hyperspectral imaging modalities enabled the comparison of reflectance, luminescence, and XRF spectra at each pixel in the image for the entire painting. By comparing the molecular and elemental spectral signatures at each pixel, this fusion of the data allowed for a more thorough identification and mapping of the painting's constituent organic and inorganic materials, revealing key information on the selection of raw materials, production sequence and the fashion aesthetics and chemical arts practiced in Egypt in the second century AD

All-optical radiofrequency modulation of Anderson-localized modes

All-optical modulation of light relies on exploiting intrinsic material nonlinearities. However, this optical control is rather challenging due to the weak dependence of the refractive index and absorption coefficients on the concentration of free carriers in standard semiconductors. To overcome this limitation, resonant structures with high spatial and spectral confinement are carefully designed to enhance the stored electromagnetic energy, thereby requiring lower excitation power to achieve significant nonlinear effects. Small mode-volume and high quality (Q)-factor cavities also offer an efficient coherent control of the light field and the targeted optical properties. Here, we report on optical resonances reaching Q - 10^5 induced by disorder on novel photonic/phononic crystal waveguides. At relatively low excitation powers (below 1 mW), these cavities exhibit nonlinear effects leading to periodic (up to - 35 MHz) oscillations of their resonant wavelength. Our system represents a test-bed to study the interplay between structural complexity and material nonlinearities and their impact on localization phenomena and introduces a novel functionality to the toolset of disordered photonics

Improved photocatalytic properties of doped titanium-based nanometric oxides

Photocatalysis is considered one of the most promising technologies for applications in the environmental field especially in the abatement of water-soluble organic pollutants. In this field, titanium dioxide nanoparticles have drawn much attention recently; however, the use of this oxide presents some limitation since it allows to obtain high photoresponse and degradation efficiency only under UV light irradiation, that represents the 3 to 4% of the solar radiation, so preventing its environmental large-scale applications under diffuse daylight. In this work the photocatalytic efficiencyoftitanium-based oxides systems containing alkaline earth metals such as barium and strontium, prepared by a simple sol-gel method was investigated, evaluating the degradation of methylene blue as model compound under UV and visible light irradiation. The results were compared with those obtained with Degussa P25 titanium dioxide. The achieved degradation percentage of methylene blue are very promising showing that under visible light irradiation it is possible to obtain a maximum dye removal percentage ~ 50 % higher than that obtained with the Degussa P25

Complex Master Slave Interferometry

A general theoretical model is developed to improve the novel Spectral Domain Interferometry method denoted as Master/Slave (MS) Interferometry. In this model, two functions, g and h are introduced to describe the modulation chirp of the channeled spectrum signal due to nonlinearities in the decoding process from wavenumber to time and due to dispersion in the interferometer. The utilization of these two functions brings two major improvements to previous implementations of the MS method. A first improvement consists in reducing the number of channeled spectra necessary to be collected at Master stage. In previous MSI implementation, the number of channeled spectra at the Master stage equated the number of depths where information was selected from at the Slave stage. The paper demonstrates that two experimental channeled spectra only acquired at Master stage suffice to produce A-scans from any number of resolved depths at the Slave stage. A second improvement is the utilization of complex signal processing. Previous MSI implementations discarded the phase. Complex processing of the electrical signal determined by the channeled spectrum allows phase processing that opens several novel avenues. A first consequence of such signal processing is reduction in the random component of the phase without affecting the axial resolution. In previous MSI implementations, phase instabilities were reduced by an average over the wavenumber that led to reduction in the axial resolution