Matter wave | EPFL Graph Search

Matter waves are a central part of the theory of quantum mechanics, being half of wave–particle duality. All matter exhibits wave-like behavior. For example, a beam of electrons can be diffracted just like a beam of light or a water wave. The concept that matter behaves like a wave was proposed by French physicist Louis de Broglie (dəˈbrɔɪ) in 1924, and so matter waves are also known as de Broglie waves. The de Broglie wavelength is the wavelength, λ, associated with a particle with momentum p through the Planck constant, h: \lambda = \frac{h}{p}. Wave-like behavior of matter was first experimentally demonstrated by George Paget Thomson and Alexander Reid's transmission diffraction experiment, and independently in the Davisson–Germer experiment, both using electrons; and it has also been confirmed for other elementary particles, neutral atoms and molecules. Introduction Background At the end of the 19th century, lig

Fast and ultrafast electron microscopies for skyrmions and plasmonics

Gabriele Berruto

In recent years, topology gained a central role in physics. We learnt that energetics could be often explained better by classes of objects defined by having qualitative differences. In today's jargon, we say they are topologically distinct. The process of creation and annihilation of physical objects with topological charge has peculiar aspects, because it cannot proceed by continuous deformations. The consequent protection of these physical states against internal and external perturbations can therefore be striking. In condensed matter, topologically-protected states are found in electronic systems in solids, spin textures, and particle or quasiparticle wave functions. Because of their general reluctance to change topological state,methods to manipulate their topological charge should be thoroughly designed. In this dissertation, I illustrate dynamical manipulation of a topological charge in two distinct -yet connected- research areas: nanoscopic spin textures and free electrons. In both cases, the manipulation is performed via the interaction of ultrashort light packets with the system under investigation. In the first, topologically nontrivial spin vortices, called skyrmions, are injected and controlled by the laser pulses. In FeGe, Bloch-type skyrmions are investigated via static, in-situ, and time-resolved Lorentz electronmicroscopy. Spin supercooling has been found responsible for the creation and stabilization of skyrmions in large regions of the phase diagram, controlling the amount of topological charge in the material. The cooling rate ensuing from the excitation of thematerial with strong laser pulses can reach tremendous values. This work enabled an estimate of the speed limit for laser-induced writing and erasing of such skyrmionic states. In the second case, circularly-polarized light is used to convert an electron plane wave into an electron vortex with nonzero topological charge. A chiral plasmon photoinduced at the edges of a nanohole in a metal transfers the vortex phase structure to the electron beam via stimulated plasmon absorption and emission. In a wider picture, the precise tailoring of the free electron wave function can be obtained by electron-photon inelastic scattering in proximity of a physical object, as extensively discussed in this thesis. The new awareness of our tools to control matter waves led to the implementation of an innovative type of time-domain holography, which can be used to image nanoscopic, propagating electromagnetic fields. Besides the single results exemplified in the different chapters, such as the topological-charge manipulation studies, this thesis contributes to the refinement of time-resolved microscopy with ultrafast electrons for the investigation of magnetic, electronic, and structural degrees of freedom. Ideas for further original experiments that could push the discussed physics to new boundaries are debated throughout the chapters.

EPFL2019

Complex index refraction tomography with sub ?/6-resolution

Yann Jérôme Michel Pascal Cotte, Christian Depeursinge, Nicolas Pavillon

The present invention discloses a method to improve the image resolution of a microscope. This improvement is based on the mathematical processing of the complex field computed from the measurements with a microscope of the wave emitted or scattered by the specimen. This wave is, in a preferred embodiment, electromagnetic or optical for an optical microscope, but can be also of different kind like acoustical or matter waves. The disclosed invention makes use of the quantitative phase microscopy techniques known in the sate of the art or to be invented. In a preferred embodiment, the complex field provided by Digital Holographic Microscopy (DHM), but any kind of microscopy derived from quantitative phase microscopy: modified DIC, Shack- Hartmann wavefront analyzer or any analyzer derived from a similar principle, such as multi-level lateral shearing interferometers or common-path interferometers, or devices that convert stacks of intensity images (transport if intensity techniques: TIT) into quantitative phase image can be used, provided that they deliver a comprehensive measure of the complex scattered wavefield. The hereby-disclosed method delivers superresolution microscopic images of the specimen, i.e. images with a resolution beyond the Rayleigh limit of the microscope. It is shown that the limit of resolution with coherent illumination can be improved by a factor of 6 at least. It is taught that the gain in resolution arises from the mathematical digital processing of the phase as well as of the amplitude of the complex field scattered by the observed specimen. In a first embodiment, the invention teaches how the experimental observation of systematically occurring phase singularities in phase imaging of sub-Rayleigh distanced objects can be exploited to relate the locus of the phase singularities to the sub-Rayleigh distance of point sources, not resolved in usual diffraction limited microscopy. In a second, preferred imbodiment, the disclosed method teaches how the image resolution is improved by complex deconvolution. Accessing the object's scattered complex field - containing the information coded in the phase - and deconvolving it with the reconstructed complex transfer function (CTF) is at the basis of the disclosed method. In a third, preferred imbodiment, it is taught how the concept of "Synthetic Coherent Transfer Function" (SCTF), based on Debye scalar or Vector model includes experimental parameters of MO and how the experimental Amplitude Point Spread Functions (APSF) are used for the SCTF determination. It is also taught how to derive APSF from the measurement of the complex field scattered by a nanohole in a metallic film. In a fourth imbodiment, the invention teaches how the limit of resolution can be extended to a limit of ?/6 or smaller based angular scanning. In a fifth imbodiment, the invention teaches how the presented method can generalized to a tomographic approach that ultimately results in super-resolved 3D refractive index reconstruction.

2011

Complex index refraction tomography with sub ?/6-resolution

Yann Jérôme Michel Pascal Cotte, Christian Depeursinge, Nicolas Pavillon

2011

Fast and ultrafast electron microscopies for skyrmions and plasmonics

Gabriele Berruto

EPFL2019