A finite-element approach to dynamical diffraction problems in reflection geometry

A finite-element approach to the numerical solution of the Takagi-Taupin equations expressed in a weak form is presented and applied to simulate the X-ray reflectivity curves, spatial intensity distributions and focusing properties of bent perfect crystals in symmetric reflection geometry. The proposed framework encompasses a new formulation of the Takagi-Taupin equations, which appears to be promising in terms of robustness and stability and supports the Fresnel propagation of the diffracted waves. The presented method is very flexible and has the potential of dealing with dynamical X-ray or neutron diffraction problems related to crystals of arbitrary shape and deformation. The reference implementation based on the commercial COMSOL Multiphysics software package is available to the relevant user community.Peer reviewe

A finite element approach to x-ray optics design

Volume: 10236 Host publication title: SPIE Proceedings Host publication sub-title: Damage to VUV, EUV, and X-ray Optics VI Isbn(print): 9781510609730-Non peer reviewe

XRF Ink Analysis of Selected Fragments from the Herculaneum Collection of the Biblioteca Nazionale di Napoli

The most commonly used ink in antiquity was carbon-based, and the main element of carbonized papyrus is carbon, making conventional computed tomography (CT-scanning) of Herculaneum scrolls difficult. However, Roman and Greek inks containing metals have recently been identified in some papyri from Egypt, changing our understanding of ink technology in antiquity. This raises hope that some rolls can be virtually unrolled by CT-scanning. Here we present the results of a preliminary analysis, aimed at identifying scrolls whose ink contains metals

Frontiers of light manipulation in natural, metallic, and dielectric nanostructures

AbstractThe ability to control light at the nanoscale is at the basis of contemporary photonics and plasmonics. In particular, properly engineered periodic nanostructures not only allow the inhibition of propagation of light at specific spectral ranges or its confinement in nanocavities or waveguides, but make also possible field enhancement effects in vibrational, Raman, infrared and fluorescence spectroscopies, paving the way to the development of novel high-performance optical sensors. All these devices find an impressive analogy in nearly-periodic photonic nanostructures present in several plants, animals and algae, which can represent a source of inspiration in the development and optimization of new artificial nano-optical systems. Here we present the main properties and applications of cutting-edge nanostructures starting from several examples of natural photonic architectures, up to the most recent technologies based on metallic and dielectric metasurfaces

Bound-state in the continuum of a photonic crystal metasurface: a platform for ultrasensitive sensing and near field amplification

Abstract The localization of the electromagnetic field at the nanoscale can play a key role in many applications, such as sensing, spectroscopy and energy conversion. In the last years, great efforts have been performed to study and realize all-dielectric loss-free nanostructures to confine the radiation without the limits imposed by the plasmonic systems. Here we demonstrate that the field enhancement in proximity of a photonic crystal metasurface supporting bound states in the continuum can be explored to boost the light-matter interaction. We design and realize an innovative sensing scheme for bulk and surface measurement with ultra-high figure of merit and apply this new configuration for studying a specific protein-protein interaction. The recognition scheme can be coupled to a fluorescence-based sensing approach, which exploits the capability of the sensor to strongly enhance fluorescence signals. Our results provide new solutions for light manipulation at the nanoscale, especially for sensing and nonlinear optics applications

Negative refraction in Photonic Crystals: thickness dependence and Pendellösung phenomenon

We show that the refracted wave at the exit surface of a Photonic Crystal (PhC) slab is periodically modulated, in positive or in negative direction, changing the slab thickness. In spite of an always increasing literature, the effect of the thickness in negative refraction on PhC's does not seem to be appropriately considered. However such an effect is not surprising if interpreted with the help of Dynamical Diffraction Theory (DDT), which is generally applied in the x-ray diffraction. The thickness dependence is a direct result of the so-called Pendellösung phenomenon. That explains the periodic exchange, inside the crystal, of the energy among direct beam (or positively refracted) and diffracted beam (or negatively refracted). The Pendellösung phenomenon is an outstanding example of the application of the DDT as a powerful and simple tool for the analysis of s electromagnetic interaction in PhC's