סמינר זה יחשב כסמינר שמיעה לתלמידי תואר שני, למי שמתחבר לסמינר דרך הזום.

You are invited to attend a lecture on Wednesday, Apr 22, 2020 14:00

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https://zoom.us/j/255986744

Tuning the Phase and Amplitude Response of Plasmonic Metasurface Etalons

By:

Danielle Ben Haim

M.Sc. student under the supervision of Prof. Tal Ellenbogen

Abstract

The research in the field of metasurfaces over the past years has shown their ability to control and manipulate light and thus form unique and novel electro-optical elements. These surfaces consist of arrays of subwavelength particles that exhibit a collective response which is governed by the particles properties, such as their material, shape and size. Understanding the physical behaviour of the particles in the subwavelength regime is what enables to control the overall effective properties of the element.

In this work we study the optical response of plasmonic metasurface etalons in reflection. The etalons consist of a metallic mirror and a plasmonic metasurface separated by wavelength-scale dielectric spacer. We explore the underlying physical mechanisms involved in their electromagnetic response and show that tuning the localized surface plasmon resonance and spacer thickness can be used to achieve both enhanced reflectivity and perfect absorption, in addition to full range phase control, and tunable regions of normal and anomalous dispersion. We characterize the spectral reflection and phase response of metasurface etalons consisting aluminum nanodisks of different radii separated from an aluminum reflector by a SiO₂ spacer. We use this approach to demonstrate a simple Hermite-Gaussian (HG) wavelength selective beam-shaping reflective mask and discuss the potential of this concept to be further extended by using multilayers to obtain multi-functional elements.

השתתפות בסמינר תיתן קרדיט שמיעה = עפ"י רישום שם מלא + מספר ת.ז.  בצ'אט

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https://zoom.us/j/282415583

Speaker: Tomer Cohen

M.Sc. student under the supervision of Prof. Lior Wolf

Sunday, April 26^th, 2020 at 14:00

     Zoom

Bidirectional One-Shot Unsupervised Domain Mapping

Abstract

We study the problem of mapping between a domain A, in which there is a single training sample and a domain B, for which we have a richer training set. The method we present is able to perform this mapping in both directions. For example, we can transfer all MNIST images to the visual domain captured by a single SVHN image and transform the SVHN image to the domain of the MNIST images. Our method is based on employing one encoder and one decoder for each domain, without utilizing weight sharing. The autoencoder of the single sample domain is trained to match both this sample and the latent space of domain B. Our results demonstrate convincing mapping between domains, where either the source or the target domain are defined by a single sample, far surpassing existing solutions.

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https://proofpoint.zoom.us/j/607284105

Speaker: Hadar Cohen-Duwek

Ph.D. student under the supervision of Hedva Sptizer and Alex Bronstein

ZOOM Seminar

Wednesday, 22^nd April at 12:00

Visual system's mechanisms and computational models for Spatio-temporal visual phenomena

Abstract

The research goal was to offer mechanisms and computational models that predict several visual spatio-temporal phenomena, which are a subgroup of the "visual illusions” phenomena.  (Visual illusions enable us to identify underling neuronal mechanisms of the visual system).

We focused on the “watercolor illusion”, the positive and the negative "aftereffect illusions" and the “reversed phi illusion”. The first group of illusions that we focused on involve the "creation" of surfaces which are triggered by edges, in both spatial and spatiotemporal domains. This type of effects are termed as filling-in processes. The second type of effects is directional motion effects and retinal processes. We suggest that the connection between these two types of effects derives from their common mechanism’s components.

For the filling in effects, we suggest a computational model that is based on a Poisson equation as heat source. Our proposed computational model is able to predict most of the filling-in effects that derive from edges, such as the assimilative and non-assimilative watercolor illusions, and the positive and negative aftereffects.

For the motion effects, we developed a computational model supported by simulations, which for the first time leads to correct predictions of both the behavioral motion effects (phi and reverse-phi), and the relevant electrophysiological and anatomical findings. This has been achieved through the well-known neuronal response: the rebound response (or "Off response"). For testing this hypothesis, we proposed a psychophysical experiment on human subjects, which demonstrated the abolishing of the aftereffect phenomenon through a noise mask. The experimental results confirmed the theoretical predictions regarding the role of the rebound mechanism.  We furthermore suggest that the reverse-phi effect is only an epiphenomenon of the rebound response of the visual system. Our findings, thus, shed new light on the comprehensive role of the rebound response as a parsimonious spatiotemporal detector for motion and additional memory tasks, such as for stabilization and navigation.