Seminar 21 -S3, Tuesday 28th March 2023, 14:00 (London Time)
Speaker: John Andreas Wyller (Norwegian University of Life Sciences -NMBU)
Title: Homogenization theory and neural field models
Abstract: In the last decades great advances have been made in mapping neural circuitry of the brain. This has been facilitated by novel experimental techniques for studies both at the single-cell and systems levels. It still remains, though, to combine all the pieces in the puzzle to a coherent picture of brain function. While single nerve cells (neurons) are fairly well understood, the signal – processing properties of the nerve-cell networks in cortex are still obscure. The growth of experimental data has led to a revival of so – called rate equation models for cell networks in nervous tissue (neural networks). In these models, the probability for firing action potentials, the key information carriers in the brain, is the main dynamical variable. These models assume the form of coupled integral and integro – differential equations, and they describe non-linearand nonlocal interactions between the population of excitatory and inhibitory neurons.
In the present talk I will discuss the properties of the continuum limit of a 2 population nonlocal Hopfield type of neuronal network model, with spatial periodic microstructure incorporated in the connectivity strength. The modelling framework is derived by means of a homogenization procedure, where the spatial nonlocalities are dealt with by means of Visintins theorem for 2-scale convergence of convolution integrals. I will discuss existence and stability of stationary localized solutions (bumps) and pattern formation though Turing type of instabilities within the framework of this model.
Seminar 22 -S3, Tuesday 4th April 2023, 14:00 (London Time)
Speaker: Arnaud Tourin (Institut Langevin, ESPCI Paris | PSL – CNRS, France)
Seminar 23 -S3, Tuesday 11th April 2023, 14:00 (London Time)
Speaker: Dragomir Neshev (ARC Centre of Excellence for Transformative Meta Optical Systems (TMOS), Australian National University)
Title: Tunable optics with ultra-thin metasurfaces
Abstract: Optical metasurfaces are sub-wavelength patterned surfaces that interact strongly with light. The field has been driven by the key advantages of this technology, including the ultimate miniaturization of optical elements, empowering novel functionalities that process hidden modalities of light, and the opportunity to tune their properties on demand. Several exciting applications have been demonstrated over the past years, including high-efficiency metalenses and holograms. However, many exciting new applications require metasurfaces with dynamically reconfigurable and programable functionalities. Such applications include 3D imaging, holographic displays, and light detection and ranging (LIDAR). This talk will overview the recent advances and challenges in reconfiguring optical metasurfaces. I will discuss metasurface tunability by controlling their surrounding environment and constituent elements. In particular, I will present the development of electrically driven thermo-optical metasurfaces to perform fast amplitude modulation. We demonstrate multi-pixel operation with over 70% transmission modulation. I will also discuss liquid crystal-tunable metasurfaces for full-range phase-only modulation. The presented developments aim to advance the field of tunable optical metasurface for real-world applications of active meta-optics.
Biography: Dragomir Neshev is the Director of the Australian Research Council Centre of Excellence for Transformative Meta-Optical Systems (TMOS) and a Professor of Physics at the Australian National University (ANU). He received a PhD degree from Sofia University, Bulgaria, in 1999. Since then, he has worked in the field of optics at several research centres around the world and joined ANU in 2002. He is the recipient of several awards and honours, including a Highly Cited Researcher (Web of Science, 2022 & 2021), a Queen Elizabeth II Fellowship (ARC, 2010), and a Marie-Curie Individual Fellowship (European Commission, 2001); and the Academic award for the best young scientist (Sofia University, 1999). His activities span several branches of optics, including meta-optics, metasurfaces, periodic photonic structures, singular optics, and plasmonics.
Seminar 24 -S3, Tuesday 18th April 2023, 14:00 (London Time)
Speaker: Federico Capasso (Harvard University, Cambridge, USA)
Seminar 26 -S3, Tuesday 2nd May 2023, 14:00 (London Time)
Speaker: Gautier Lefebvre (Laboratoire Roberval, Université de Technologie de Compiègne, France)
Seminar 28 -S3, Tuesday 16th Mai 2023, 14:00 (London Time)
Speaker: Alexandre Bouhelier (CNRS, Laboratoire Interdisciplinaire Carnot de Bourgogne UMR 6303 Université Bourgogne Franche-Comté, France)
Title: The glowing fate of hot electrons
Abstract: I will describe a new series of nanoscale components based on a reversible transduction between electron and a photon using optical gap antennas. Our concept provides a novel approach where the light source and the detector can be integrated into a single metallic nanostructure. At the core of the device is an atomic-scale tunnel gap whereby optical rectification, inelastic tunneling, and hot carriers can reciprocally mix photons and electrons with ultrafast conversion dynamics. We will discuss the peculiarity of the broadband spectrum emitted from the antenna feed by a decaying population of hot electrons. The source can be readily integrated to plasmonic and photonic waveguides. The co-integration of atomic-scale optical functional devices with an electronic transduction offers a disruptive solution to interface photons and electrons at this ultimate length scale.
Biography: Alexandre Bouhelier has been a CNRS researcher since December 2005. He obtained his doctoral thesis in Physics at the University of Basel (Switzerland) in 2001 where he specialized in near field optics. Following his doctorate, A. Bouhelier went to The Institute of Optics at the University of Rochester (NY, USA) as a postdoc on a grant from the Swiss national research fund (2001-2003). His work has been centered on the enhancements of the electromagnetic field applied to the optical near field. From 2003 to 2005, A. Bouhelier was a researcher at the Center for Nanoscale Materials at the Argonne National Laboratory (Il, USA) where he specialized in plasmonics. He joined the Carnot Interdisciplinary Laboratory in Burgundy and participated in the development of new components for controlling the surface plasmon. He obtained his Habilitation to Direct Research in 2001. He was promoted to Director of Research in 2014.