7 research outputs found
Exploring plenoptic properties of correlation imaging with chaotic light
In a setup illuminated by chaotic light, we consider different schemes that
enable to perform imaging by measuring second-order intensity correlations. The
most relevant feature of the proposed protocols is the ability to perform
plenoptic imaging, namely to reconstruct the geometrical path of light
propagating in the system, by imaging both the object and the focusing element.
This property allows to encode, in a single data acquisition, both
multi-perspective images of the scene and light distribution in different
planes between the scene and the focusing element. We unveil the plenoptic
property of three different setups, explore their refocusing potentialities and
discuss their practical applications.Comment: 9 pages, 4 figure
Phénomènes exotiques dans le nouveau système d’échelle de spin frustrés Li2Cu2O(SO4)2
The study of frustrated spin-1/2 ladder systems is a fundamental task in condensed matter physics, as they fulfill all the requirements favouring the emergence of new and exotic phenomena. However, despite decades of theoretical work devoted to the study of these spin ladders, real material realizations of such systems still remain limited. In this thesis, we investigate the magnetic properties of a new compound Li2Cu2O(SO4)2. This system appears as a very rare realization of a S=1/2 frustrated two-leg spin ladder in its high-temperature tetragonal structure, where geometrical frustration arises from competing interactions along the legs. Moreover, temperature dependent neutron and X-ray diffraction reveal the presence of a structural phase transition occurring at around 125 K. Combining the experimental and theoretical approaches, we demonstrate that this weak and progressive distortion, while maintaining the global geometry of a ladder, induces the formation of a staggered dimer structure through a large magnetoelastic coupling, removing most of the magnetic frustration. Furthermore, we present the first detailed investigation of the low-temperature magnetic excitations of Li2Cu2O(SO4)2 combining magnetic susceptibility, infrared spectroscopy and inelastic neutron scattering measurements. Experimental observations are qualitatively explained by exact diagonalization and higher-order perturbation calculations carried out on the basis of the dimerized geometry derived from first principle calculations.L’étude des systèmes d’échelles de spin-1/2 frustrés est une tâche fondamentale dans la physique de la matière condensée, car ils répondent aux exigences favorisant l’émergence de phénomènes nouveaux et exotiques. Cependant, malgré des décennies de travaux théoriques consacrés à l’étude de ces systèmes, leurs réalisations restent encore limitées. Dans cette thèse, nous étudions les propriétés magnétiques d’un nouveau composé Li2Cu2O(SO4)2. Ce système apparaît comme une très rare réalisation d’échelle de spin-1/2 frustrée à deux jambes dans sa phase tétragonale à haute température, où la frustration géométrique provient des interactions concurrentes le long des jambes. De plus, la diffraction de neutrons et de rayons X en fonction de la température révèlent la présence d’une transition de phase structurale à environ 125 K, impliquant une très faible distorsion de la structure. En combinant les approches expérimentale et théorique, nous démontrons que cette distorsion faible et progressive, tout en maintenant la géométrie globale d’une échelle, induit la formation d’une structure de dimères alternés à travers un grand couplage magnétoélastique, éliminant la plupart des frustrations magnétiques. En outre, nous présentons la première étude détaillée des excitations magnétiques à basse température de Li2Cu2O(SO4)2 combinant la susceptibilité magnétique, la spectroscopie infrarouge et les mesures de diffusion inélastique de neutrons. Les observations expérimentales sont qualitativement expliquées par des calculs de diagonalisation exacte et perturbations d’ordre élevés effectués sur la base de la géométrie dimérisée dérivée des calculs de premiers principes
Quantum-mechanical force balance between multipolar dispersion and Pauli repulsion in atomic van der Waals dimers
The structure and stability of atomic and molecular systems with van der
Waals (vdW) bonding are often determined by the interplay between attractive
dispersion interactions and repulsive interactions caused by electron
confinement. Arising due to different mechanisms -- electron correlation for
dispersion and the Pauli exclusion principle for exchange-repulsion -- these
interactions do not appear to have a straightforward connection. In this paper,
we use a coarse-grained approach for evaluating the exchange energy for two
coupled quantum Drude oscillators and investigate the mutual compensation of
the attractive and repulsive forces at the equilibrium distance within the
multipole expansion of the Coulomb potential. This compensation yields a
compact formula relating the vdW radius of an atom to its multipole
polarizabilities, , where
is the multipole rank and is a conversion factor. Such a relation is
compelling because it connects an electronic property of an isolated atom
(atomic polarizability) with an equilibrium distance in a dimer composed of two
closed-shell atoms. We assess the accuracy of the revealed formula for
noble-gas, alkaline-earth, and alkali atoms and show that the can be
assumed to be universal constants. Besides a seamless definition of vdW radii,
the proposed relation can also be used for the efficient determination of
atomic multipole polarizabilities solely based on the corresponding dipole
polarizability and the vdW radius. Finally, our work provides a basis for the
construction of efficient and minimally-empirical interatomic potentials by
combining multipolar interatomic exchange and dispersion forces on an equal
footing.Comment: 15 pages, 4 figure
DEVICE AND PROCESS FOR THE CONTEMPORARY CAPTURE OF STANDARD AND PLENOPTIC IMAGES
The object of the present invention is a plenoptic image capturing technique to capture images in the field of photography, cinematography, microscopy and stereoscopy.
In particular, the plenoptic shooting process according to the present invention is named "Correlation Plenoptic Imaging" (CPI), i.e. it refers to a plenoptic capture of images based on the spatio-temporal correlation of light intensities recorded by sensors arranged so as to capture the spatial and angular measures of the image
“Dispositivo e procedimento di acquisizione plenottica di immagini”.
La presente invenzione ha per oggetto una tecnica di acquisizione plenottica di immagini nel campo della fotografia, cinematografia, microscopia e stereoscopia.
In particolare, il procedimento di ripresa plenottica secondo la presente invenzione prende il nome di “Correlation Plenoptic Imaging” (CPI), ovvero fa riferimento ad un’acquisizione plenottica di immagini basata sulla correlazione spazio-temporale delle intensità luminose registrate dai sensori predisposti ad acquisire la misura spaziale ed angolare dell’immagin