Curved mirror | EPFL Graph Search

A curved mirror is a mirror with a curved reflecting surface. The surface may be either convex (bulging outward) or concave (recessed inward). Most curved mirrors have surfaces that are shaped like part of a sphere, but other shapes are sometimes used in optical devices. The most common non-spherical type are parabolic reflectors, found in optical devices such as reflecting telescopes that need to image distant objects, since spherical mirror systems, like spherical lenses, suffer from spherical aberration. Distorting mirrors are used for entertainment. They have convex and concave regions that produce deliberately distorted images. They also provide highly magnified or highly diminished (smaller) images when the object is placed at certain distances. Convex mirrors A convex mirror or diverging mirror is a curved mirror in which the reflective surface bulges towards the light source. Convex mirrors reflect light outwards, therefore they are not used to focus light. Such

Surface-based luminescence measurement substrate

Raphaël Barbey, Nicolas Maxime André Descharmes

Surface-based measurement substrate including: • - at least one optical cavity layer (7); • - a first optical mirror (9) and a second optical mirror (11), the first and second optical mirrors enclosing the optical cavity layer and defining an optical cavity, wherein the first optical mirror and the second optical mirror are attached or fixed to the optical cavity layer to sandwich the optical cavity layer between the first and second mirrors; and • - an interface layer or interface coating (15) provided on the first mirror or the second mirror, the interface layer or coating being configured to receive or hold at least one entity (4) comprising at least one electromagnetic radiation emitting marker (3).

2020

Synthesis and properties of heterostructures in nanowires and 2-D materials

Akshay Balgarkashi

Modern solid-state devices were made possible by the discovery of semiconductor heterostructures. Heterostructures offer the ability to fabricate low-dimensional nanostructures such as quantum dots which can restrain carriers in all three-directions. Quantum dots as single photon sources can be used as building blocks in quantum photonics and information processing applications. In this thesis, we explore heterostructures in nanowires and 2-D materials towards fabrication of quantum dots. In the first part, we show how facet-driven nanostructure self-assembly can be used to grow axial and radial QDs in lattice-mismatched NW heterostructures. We investigate the growth of InAs/GaAs nanowire heterostructure arrays on Si substrates using the Ga-catalyzed method. We show how the nanowire tip morphology affects the formation of axial In(Ga)As clusters. The occurrence of In-rich clusters on the nanowires is elucidated by electron microscopy. We also show how the In(Ga)As cluster formation on the nanowire sidewalls is driven by the convex nature of the {11-2} corner facets. Cathodoluminescence and photoluminescence maps close to the NW tip evidence the presence of optically active emission centers along the NW sidewalls. The second part is dedicated to heterostructures using monolayer 2-D transition-metal dichalcogenides. Firstly, we study the heterojunction between monolayer MoS2 and gold. We provide a detailed understanding of the microscopic origins behind Raman mode splitting in monolayer MoS2 exfoliated on gold substrates. We show that splitting in the Raman modes is a convolution of two effects: structural perturbations in MoS2 due to the Au-S interaction and breaking of symmetry rules by the metallic plasmons. We confirm the proposed hypothesis by using Al as the metal which does not show any peak splitting. In the last part, we successfully combine monolayer MoS2 with a GaAs NW array as a first step towards integrating monolayer 2-D materials with III-V nanowire arrays. Using detailed structural investigation, we show three different configurations of the MoS2 monolayer on NWs. Through confocal Raman and photoluminescence mapping, we show variations in the properties of the monolayer due to nanowires. We show how the vibrational properties are mainly affected by strain and charge transfer due to the nanowires. A blueshift in the luminescence attributing to an enhanced dielectric screening due to GaAs nanowires is observed. We show how III-V nanowires can be used to engineer the properties and enhance light extraction from monolayer 2-D materials.

EPFL2022

Optical Mirror from Laser-Trapped Mesoscopic Particles

Jean-Marc Fournier, Johann Rohner

Trapping of mesoscopic particles by optical forces usually relies on the gradient force, whereby particles are attracted into optical wells formed by landscaping the intensity of an optical field. This is most often achieved by optical Gaussian beams, interference patterns, general phase contrast methods, or other mechanisms. Hence, although the simultaneous trapping of several hundreds of particles can be achieved, these particles remain mostly independent with negligible interaction. Optical matter, however, relies on close packing and binding forces, with fundamentally different electrodynamic properties. In this Letter, we build ensembles of optically bound particles to realize a reflective surface that can be used to image an object or to focus a light beam. To our knowledge, this is the first experimental proof of the creation of a mirror by optical matter, and represents an important step toward the realization of a laser-trapped mirror (LTM) in space. From a theoretical point of view, optically bound close packing requires an exact solver of Maxwell's equations in order to precisely compute the field scattered by the collection of particles. Such rigorous calculations have been developed and are used here to study the focusing and resolving power of an LTM.

Amer Physical Soc2014

Synthesis and properties of heterostructures in nanowires and 2-D materials

Akshay Balgarkashi

EPFL2022