Écran à cristaux liquides

Résumé

thumb|right|Dans une Tablet PC. thumb|right|Dans un appareil photographique numérique. L'écran à cristaux liquides ou LCD (de l'anglais liquid crystal display) (ACL au Québec pour affichage à cristaux liquides) permet la création d’écrans plats à faible consommation d'électricité. Ces écrans sont utilisés dans presque tous les affichages électroniques. Histoire Les premiers panneaux d’affichage à cristaux liquides ont été présentés en 1971, mais il faut attendre 1985 pour que Matsushita propose un écran plat d’une taille et d'une résolution suffisante pour être utilisable sur des micro-ordinateurs. Dès 1984, c’est le laboratoire central de Thomson qui a développé le premier LCD en couleurs. Les LCD sont utilisés depuis la fin des années 1990 en noir et blanc, puis en couleur depuis les débuts des années 2000 dans les téléphones portables, les ordinateurs personnels, les téléviseurs, les ordinateurs de bord pour les avions et les voitures. Les premiers écrans plats comme

Source officielle

https://fr.wikipedia.org/wiki/%C3%89cran_%C3%A0_cristaux_liquides

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Optofluidic modulator based on peristaltic nematogen microflows

Julien Cuennet, Luciano De Sio, Demetri Psaltis, Andreas Vasdekis

Nematogens rotate by the application of external fields, thereby enabling optical modulation. This principle has had a profound impact on our daily lives through the plethora of liquid-crystal displays in use around us(1,2). However, the wider use of nematic liquid crystals, particularly in microdisplays(3) and information processing, has been hampered by their slow response times. In nematogens, rotational and translational molecular motions are coupled(4), so flow is inevitably linked with optical modulation(5,6). This linkage motivated us to fuse microfluidics with anisotropic liquids and introduce an optofluidic(7,8) modulator that exhibits a submillisecond (250 mu s) symmetric response and can operate at frequencies up to 1 kHz. The modulator is based on peristaltic nematogen microflows(9) realized in polydimethylsiloxane microfluidics. The latter simultaneously permits peristalsis by means of elastomeric deformation, nematogen alignment and rapid prototyping through cast-moulding. Together with large-scale, vertical integration and piezoelectric nanotechnologies, this optofluidic paradigm can enable high-density and three-dimensional architectures of fast modulators.

2011

Chargement

This thesis describes innovative techniques for reducing speckle noise and improving the intensity profile of the speckle correlation fringes. The methods are based on reducing the range of the modulation intensity values of the speckle interference pattern. After the fringe pattern is corrected adaptively at each pixel, a simple morphological filtering of the fringes is sufficient to obtain smoothed fringes. The concepts are presented both analytically and by simulation by using computer-generated speckle patterns and experimental verifications are performed wherever possible. A new generalized method for designing continuous amplitude-only pupil filters for transverse superresolution using a nonlinear programming method is also presented. The thesis emphasises the principal advantage of amplitude-only filters over their phase-only counterparts, that the side lobe intensities can be highly reduced along with the spot size. A quantitative comparison with continuous phase-only filters as well as the two-zone binary phase filter is shown with respect to spot size and ratio of side lobe to central peak intensity. The work is extended to combine the advantages of amplitude and phase filters in one complex filter that performs better than either phase or amplitude filters designed so far. The performance here refers to having a smaller spot size along with higher peak to side lobe intensity ratio. Using numerical simulation the limitations of phase and amplitude filters are assessed. The experimental verification of the designed combination filter is performed with two LCD spatial light modulators used for displaying separately the phase and amplitude part of the filter. Results obtained from this setup confirm the simulation. Finally, the effect of optical superresolution on speckle correlations is studied. Simulations reveal that using a lateral super-resolution pupil filter more than twice the out of plane correlation length of the clear pupil can be achieved. This means that the measurement range in speckle correlation measurements doubles. To verify the correlation length an experiment is performed using a liquid crystal (LCD) spatial light modulator as a programmable superresolution filter. The results corroborate the simulation.

EPFL2007

Chargement

Long Spin Lifetime in Rare-Earth Single-Atom Magnets at Surfaces

Boris Sorokin

Further miniaturisation of magnetic storage devices requires an advent of new types of magnets, since classical ferromagnetic materials show lack of remanence at nano- and subnanoscale. A single atom can represent the smallest possible bit of information. Even though the isolated single atoms are paramagnetic, the interaction of surface adsorbed atoms with a substrate can result in high magnetic anisotropy energy and long magnetisation lifetime. In this thesis the magnetic properties of surface supported rare-earth single atoms are investigated with X-ray absorption spectroscopy, X-ray magnetic circular dichroism and multiplet simulations. The first goal of the project was to find new adatom/substrate combinations that exhibit a long adatom magnetic lifetime, possibly extending the current limits of the atomic magnetic moment stability to higher temperatures and longer spin relaxation times. The second objective was to implement the external electric field control of the adatom magnetic properties.Firstly, we present the experimental and theoretical research on Dy and Ho single atoms deposited on BaO. A comparison of our results with similar studies sheds light on the impact of the substrate crystal field, in particular Dy-O bond covalency, on the magnetic stability of the rare-earth adatoms. Next, the detailed experimental investigation of Dy single atoms on ZnO is presented. This adatom/substrate pair is used as first attempt to implement the electric field control of the adatom magnetic properties. Lastly, we study the Dy adatoms on graphene layers grown on various metals. The vibrational modes of the metallic substrates are shown to strongly affect the Dy spin lifetime, while addition of a second graphene layer does not allow to significantly improve the adatom magnetic stability.

EPFL2022

Chargement

EPFL2007