Second and Third Harmonic Generation in Metal-Based Nanostructures

We present a new theoretical approach to the study of second and third harmonic generation from metallic nanostructures and nanocavities filled with a nonlinear material, in the ultrashort pulse regime. We model the metal as a two-component medium, using the hydrodynamic model to describe free electrons, and Lorentz oscillators to account for core electron contributions to both the linear dielectric constant and to harmonic generation. The active nonlinear medium that may fill a metallic nanocavity, or be positioned between metallic layers in a stack, is also modeled using Lorentz oscillators and surface phenomena due to symmetry breaking are taken into account. We study the effects of incident TE- and TM-polarized fields and show that a simple re-examination of the basic equations reveals additional exploitable dynamical features of nonlinear frequency conversion in plasmonic nanostructures.Comment: 33 pages, including 11 figures and 74 references; corrected affiliations and some typo

Singularity-driven Second and Third Harmonic Generation in a {\epsilon}-near-zero nanolayer

We show a new path to {\epsilon}~0 materials without resorting to metal-based metamaterial composites. A medium that can be modeled using Lorentz oscillators usually displays {\epsilon}=0 crossing points, e.g. {\epsilon}=0 at {\lambda}~7{\mu}m and 20{\mu}m for SiO2 and CaF2, respectively. We show that a Lorentz medium yields a singularity-driven enhancement of the electric field followed by dramatic lowering of thresholds for a plethora of nonlinear optical phenomena. We illustrate the remarkable enhancement of second and third harmonic generation in a layer of {\epsilon}~0 material 20nm thick, and discuss the role of nonlinear surface sources

Thermal neutron detection by means of Timepix3

Thermal neutron detection plays a crucial role in numerous scientific and technical applications such as nuclear reactor physics, particle accelerators, radiotherapy,materials analysis and space exploration. There are several challenges associated with the accurate identification and quantification of thermal neutrons. The present work proposes a detailed characterization of a Timepix3 (TPX3) detector equipped with a Lithium Fluoride (6LiF) converter in order to study its response to thermal neutrons that are identified through the 6Li(n,α)3H reaction. The TPX3-based test system has been installed at the HOTNES facility in ENEA and the analysis highlighted its excellent performance showing high effectiveness in the identification of neutrons through morphological analysis of tracks produced by alpha and triton particles, after accurate discrimination from the gamma background. With the use of Monte Carlo simulations, it has been demonstrated that the main contribution is due to tritons and its signal can be used effectively in the identification of thermal neutrons obtaining an efficiency of 0.9 % for 25 meV neutrons. This allows the TPX3 to have important applications as an environmental monitor for thermal neutrons. This monitoring system can be simply realized and is easy to manage because of its compact size and its digital acquisition that allows a real-time analysis

Enhanced third harmonic generation from the epsilon-near-zero modes of ultrathin films

We experimentally demonstrate efficient third harmonic generation from an indium tin oxide (ITO) nanofilm (lambda/42 thick) on a glass substrate for a pump wavelength of 1.4 um. A conversion efficiency of 3.3x10^-6 is achieved by exploiting the field enhancement properties of the epsilon-near-zero (ENZ) mode with an enhancement factor of 200. This nanoscale frequency conversion method is applicable to other plasmonic materials and reststrahlen materials in proximity of the longitudinal optical phonon frequencies.Comment: 13 pages, 5 figure

Enhancement and Suppression of Transmission in 3-D Nanoslits Arrays with 1-and 2-D Periodicities

ABSTRACT We investigate the transmission properties of arrays of three-dimensional (3-D) gold patches having one-and twodimensional (1-and 2-D) periodicities, and describe the interaction of cavity and surface plasmon modes. We vary the main geometrical parameters to assess similarities and emphasize differences between 1-D and 2-D periodic patterns. We analyze the spectral response as a function of incident angle and polarization to corroborate our findings. We will also consider form and air filling factors of the grating to assess our ability to control the transmission spectrum. In particular, we observe strong inhibition of the transmission when the impinging wave-vector parallel to the surface of the metal matches the surface plasmon wave-vector of the unperturbed air-gold interface when added to the grating lattice wave-vector. This phenomenon favors the opening of a plasmonic band gap, featuring the suppression of transmission and simultaneous coupling to back-radiation (reflections) of the unperturbed surface plasmon. High-Q, resonating modes occur at the edges of the forbidden band, boosting the energy transfer across the grating thus providing enhanced transmission and broadside directivity at the exit side of the grating

Gender-dependent differences in plasma matrix metalloproteinase-8 elevated in pulmonary tuberculosis.

Tuberculosis (TB) remains a global health pandemic and greater understanding of underlying pathogenesis is required to develop novel therapeutic and diagnostic approaches. Matrix metalloproteinases (MMPs) are emerging as key effectors of tissue destruction in TB but have not been comprehensively studied in plasma, nor have gender differences been investigated. We measured the plasma concentrations of MMPs in a carefully characterised, prospectively recruited clinical cohort of 380 individuals. The collagenases, MMP-1 and MMP-8, were elevated in plasma of patients with pulmonary TB relative to healthy controls, and MMP-7 (matrilysin) and MMP-9 (gelatinase B) were also increased. MMP-8 was TB-specific (p<0.001), not being elevated in symptomatic controls (symptoms suspicious of TB but active disease excluded). Plasma MMP-8 concentrations inversely correlated with body mass index. Plasma MMP-8 concentration was 1.51-fold higher in males than females with TB (p<0.05) and this difference was not due to greater disease severity in men. Gender-specific analysis of MMPs demonstrated consistent increase in MMP-1 and -8 in TB, but MMP-8 was a better discriminator for TB in men. Plasma collagenases are elevated in pulmonary TB and differ between men and women. Gender must be considered in investigation of TB immunopathology and development of novel diagnostic markers

Optical Properties of Ordered Plasmonic Nanostructures in Linear and Nonlinear Regimes

ABSTRACT In this paper we review our recent advances in subwavelength plasmonic structures in linear and nonlinear regimes. We show several examples of subwavelength plasmonic devices in different configurations and schemes. We emphasize how these devices can be exploited for many applications, such as sensing, spectroscopy, photovoltaics and optical communications. Finally we will illustrate some challenges that are still open and need to be fulfilled. Keywords: plasmonics, plasmonic resonance, scattering, field enhancement, thin film, nonlinear harmonic generation. INTRODUCTION The propagation of Surface Plasmon Polaritons (SPPs) has gained great interest in the last decades since it has been demonstrated that their excitation on metal gratings or metal nanostructures can be usefully exploited to solve several problems relative to many applications, such as Raman spectroscopy, sensing, data storage, light emission and amplification as well as absorption enhancement for energy harvesting purpose