A DGTD method for the numerical modeling of the interaction of light with nanometer scale metallic structures taking into account non-local dispersion effects

The interaction of light with metallic nanostructures is of increasing interest for various fields of research. When metallic structures have sub-wavelength sizes and the illuminating frequencies are in the regime of metal's plasma frequency, electron interaction with the exciting fields have to be taken into account. Due to these interactions, plasmonic surface waves can be excited and cause extreme local field enhancements (e.g. surface plasmon polariton electromagnetic waves). Exploiting such field enhancements in applications of interest requires a detailed knowledge about the occurring fields which can generally not be obtained analytically. For the latter mentioned reason, numerical tools as well as a deeper understanding of the underlying physics, are absolutely necessary. For the numerical modeling of light/structure interaction on the nanoscale, the choice of an appropriate material model is a crucial point. Approaches that are adopted in a first instance are based on local (i.e. with no interaction between electrons) dispersive models e.g. Drude or Drude-Lorentz models. From the mathematical point of view, when a time-domain modeling is considered, these models lead to an additional system of ordinary differential equation which is coupled to Maxwell's equations. When it comes to very small structures in a regime of 2~nm to 25~nm, non-local effects due to electron collisions have to be taken into account. Non-locality leads to additional, in general non-linear, system of partial differential equations and is significantly more difficult to treat, though. Nevertheless, dealing with a linear non-local dispersion model is already a setting that opens the route to numerous practical applications of plasmonics. In this work, we present a Discontinuous Galerkin Time-Domain (DGTD) method able to solve the system of Maxwell equations coupled to a linearized non-local dispersion model relevant to plasmonics. While the method is presented in the general 3d case, numerical results are given for 2d simulation settings only

Simulating 3D periodic structures at oblique incidences with discontinuous Galerkin time-domain methods: theoretical and practical considerations

International audienceIn this work, we focus on the development of the use of Periodic Boundary Conditions (PBC) with sources at oblique incidence in a Discontinuous Galerkin Time Domain (DGTD) framework. Whereas in the context of the Finite Difference Time Domain (FDTD) methods, an abundant literature can be found, for DGTD, the amount of contributions reporting on such methods is remarkably low. In this paper, we supplement the existing references using the field transform technique with an analysis of the continuous system using the method of characteristics and provide an energy estimate. Furthermore, we also study the discrete stability of the resulting DGTD scheme. Additional details about sources, observables (reflectance, transmittance and diffraction efficiency), and the use of Complex Frequency-Shifted Perfectly-Matched Layers (CFS-PMLs) in this framework are also given. After numerical validations, two realistic test-cases are considered in the context of nanophotonics with the Diogenes DGTD solver (http://diogenes.inria.fr)

Discontinuous Galerkin Time Domain Methods for Nonlocal Dispersion Models and Electron Beam Modeling in the Context of Nanoplasmonics

International audienceThis contribution consists of two main parts: non-local dispersion models and the numerical modeling of single electron beams. Both subjects are discussed in the context of computational nanophotonics for metallic nano-structures. Non-local dispersion models take into account the non-local nature of mutual electron interaction in the electron gas for metallic nano-structures. Contrary to local models (Drude, Drude-Lorentz,...), non-local models allow additional solutions such as electron density waves that can travel inside the metal bulk [1, 2]. However, these effects only appear for structures at the size of 2 nm to 25 nm. Electron beams traveling in the vicinity or inside metallic nano structures excite plasmons. Microscopy techniques like Electron Energy Loss Spectroscopy (EELS) and Cathodoluminescence (CL) are examples of applications. These technologies exploit the electron-plasmon interaction in order to measure plasmonic mode patterns [3]. Both physical aspects are numerically modeled in 3D discontinuous Galerkin time domain (DGTD) framework in order to provide a deeper understanding of the underlying physics

Discontinuous Galerkin Time Domain Methods for Nonlocal Dispersion Models and Electron Beam Modeling in the Context of Nanoplasmonics

International audienceThis contribution consists of two main parts: non-local dispersion models and the numerical modeling of single electron beams. Both subjects are discussed in the context of computational nanophotonics for metallic nano-structures. Non-local dispersion models take into account the non-local nature of mutual electron interaction in the electron gas for metallic nano-structures. Contrary to local models (Drude, Drude-Lorentz,...), non-local models allow additional solutions such as electron density waves that can travel inside the metal bulk [1, 2]. However, these effects only appear for structures at the size of 2 nm to 25 nm. Electron beams traveling in the vicinity or inside metallic nano structures excite plasmons. Microscopy techniques like Electron Energy Loss Spectroscopy (EELS) and Cathodoluminescence (CL) are examples of applications. These technologies exploit the electron-plasmon interaction in order to measure plasmonic mode patterns [3]. Both physical aspects are numerically modeled in 3D discontinuous Galerkin time domain (DGTD) framework in order to provide a deeper understanding of the underlying physics

Amygdala and subcortical vision: recognition of threat and fear

The amygdala (Am) is a relatively voluminous gray substance, located in the depth of the ventromedial temporal lobe. The Am has diverse afferent and efferent connections throughout the neuraxis, and is involved in the modulation of neuroendocrine functions, visceral effector mechanisms, and in complex patterns of behavior: learning and memory, aggression and defense, pain modulation, reproduction, food intake, etc. A recently revealed important function of the Am is that it acts as the brain 'lighthouse' which constantly monitors the environment for stimuli which signal a threat to the organism. The data from patients with extensive lesions of the striate cortex indicate that unseen fearful and fear-conditioned faces elicit increased Am responses. Thus, also extrageniculostriate pathways are involved. A multisynaptic pathway from the retina to the Am via the superior colliculus and several thalamic nuclei was recently suggested. We here present data based on retrograde neuronal labeling that the parabigeminal nucleus emits a substantial bilateral projection to the Am. This small cholinergic nucleus (Ch8 group) in the midbrain tegmentum is a subcortical relay visual center that is reciprocally connected with the superior colliculus. We suggest the existence of a second extrageniculostriate multisynaptic connection to Am: retina - superior colliculus - parabigeminal nucleus - Am. This pathway might be very effective since all tracts listed above are bilateral. The function of the Am by the rapid response to the sources of threat before conscious detection is significantly altered by various neuropsychiatric diseases.Biomedical Reviews 2008; 19: 1-16

Simulation of three-dimensional nanoscale light interaction with spatially dispersive metals using a high order curvilinear DGTD method

In this work, we present and study a flexible and accurate numerical solver in the context of three-dimensional computational nanophotonics. More precisely, we focus on the propagation of electromagnetic waves through metallic media described by a non-local dispersive model. For this model, we propose a discretization based on a high-order Discontinuous Galerkin time-domain method, along with a low-storage Runge-Kutta time scheme of order four. The semi-discrete stability of the scheme is analyzed for classical numerical fluxes, i.e. centered and upwind.Furthermore, the numerical treatment is enriched with an enhanced approximation of the geometry based on isoparametric curvilinear meshes. We finally assess our approach on several test cases, from academic to more physical ones

Discontinuous Galerkin Time Domain Methods for Nonlocal Dispersion Models and Electron Beam Modeling in the Context of Nanoplasmonics

International audienceWe present recent advancements of the development of our DGTD solvers for computational nanophotonics, particularly for metallic nanostructures irradiated by laser pulses or electron beams. By this means, we firstly discuss the numerical treatment of a nonlocal dispersion model for the electron gas which is necessary for structures in the regime of 2 nm to 25 nm. Subsequently, we deal with the modeling of electron beams in 3D simulations for e.g. electron energy loss spectroscopy or cathodoluminescence

Optimization and uncertainty quantification of gradient index metasurfaces

The design of intrinsically flat two-dimensional optical components, i.e., metasurfaces, generally requires an extensive parameter search to target the appropriate scattering properties of their constituting building blocks. Such design methodologies neglect important near-field interaction effects, playing an essential role in limiting the device performance. Optimization of transmission, phase-addressing and broadband performances of metasurfaces require new numerical tools. Additionally, uncertainties and systematic fabrication errors should be analysed. These estimations, of critical importance in the case of large production of metaoptics components, are useful to further project their deployment in industrial applications. Here, we report on a computational methodology to optimize metasurface designs. We complement this computational methodology by quantifying the impact of fabrication uncertainties on the experimentally characterized components. This analysis provides general perspectives on the overall metaoptics performances, giving an idea of the expected average behavior of a large number of devices

The Long-Baseline Neutrino Experiment: Exploring Fundamental Symmetries of the Universe

The preponderance of matter over antimatter in the early Universe, the dynamics of the supernova bursts that produced the heavy elements necessary for life and whether protons eventually decay --- these mysteries at the forefront of particle physics and astrophysics are key to understanding the early evolution of our Universe, its current state and its eventual fate. The Long-Baseline Neutrino Experiment (LBNE) represents an extensively developed plan for a world-class experiment dedicated to addressing these questions. LBNE is conceived around three central components: (1) a new, high-intensity neutrino source generated from a megawatt-class proton accelerator at Fermi National Accelerator Laboratory, (2) a near neutrino detector just downstream of the source, and (3) a massive liquid argon time-projection chamber deployed as a far detector deep underground at the Sanford Underground Research Facility. This facility, located at the site of the former Homestake Mine in Lead, South Dakota, is approximately 1,300 km from the neutrino source at Fermilab -- a distance (baseline) that delivers optimal sensitivity to neutrino charge-parity symmetry violation and mass ordering effects. This ambitious yet cost-effective design incorporates scalability and flexibility and can accommodate a variety of upgrades and contributions. With its exceptional combination of experimental configuration, technical capabilities, and potential for transformative discoveries, LBNE promises to be a vital facility for the field of particle physics worldwide, providing physicists from around the globe with opportunities to collaborate in a twenty to thirty year program of exciting science. In this document we provide a comprehensive overview of LBNE's scientific objectives, its place in the landscape of neutrino physics worldwide, the technologies it will incorporate and the capabilities it will possess.Comment: Major update of previous version. This is the reference document for LBNE science program and current status. Chapters 1, 3, and 9 provide a comprehensive overview of LBNE's scientific objectives, its place in the landscape of neutrino physics worldwide, the technologies it will incorporate and the capabilities it will possess. 288 pages, 116 figure