Les fibres optiques sont communément utilisées en astronomie pour lier les télescopes aux spectrographes. Cet exposé propose un résumé des points suivants :
- Avantages et inconvénients
- Propriétés des fibres: transmission, dégradation d'ouverture, bruit modal, et mélange photométrique
- Couplage au télescope - fibre et couplage fibre - collimateur
- Découpeur d'image et pouvoir de résolution
Un exemple concret d'un spectrographe échelle fermera l'exposé

Contact angle hysteresis (CAH), where the motion of a contact line between a liquid interface and a solid substrate is pinned by the physical roughness and/or chemical inhomogeneity on the solid surface, is an outstanding problem in interfacial dynamics and has been with us for many years. Despite of numerous efforts, one still has a poor understanding of CAH on many ambient solid surfaces of interest. The study of CAH is of fundamental interest for our general understanding of a common class of problems involving elastic dynamics in random force fields and also has immense practical applications in tertiary oil recovery, drag reduction, advanced materials and microfluidics. In this talk I will present our recent experimental efforts in developing an atomic force microscope (AFM) based hanging fiber probe for the study of contact line dissipation and pinning-depinning dynamics [1-3]. With this new technique, AFM is used as a force sensor to measure the speed-dependent capillary force hysteresis and relaxation of a moving contact line formed on a long vertical glass fiber of a few microns in diameter with one end glued onto a AFM cantilever and the other end in contact with a liquid-air interface. Applications of this technique to the study of contact line dissipation and wetting dynamics will be discussed.

*Work done in collaboration with Dongshi Guan, Yongjian Wang, Elisabeth Charlaix and was supported by the Research Grants Council of Hong Kong SAR.

[1] “Asymmetric and speed-dependent capillary force hysteresis and relaxation of a suddenly stopped moving contact line,” D.-S. Guan, Y.-J. Wang, E. Charlaix and P. Tong, Phys. Rev. Lett. 116, 066102 (2016).

[2] “Understanding of Contact Angle Hysteresis on an Ambient Solid Surface,” Y. J. Wang, S. Guo, H.-Y. Chen, and P. Tong, Phys. Rev. E 93, 052802 (2016).

[3] “Simultaneous observation of asymmetric speed-dependent contact force hysteresis and slow relaxation of a suddenly stopped moving contact line,” D.-S. Guan, Y.-J. Wang, E. Charlaix and P. Tong, Phys. Rev. E 94, 042802 (2016).

L’analyse présentée est basée sur les mesures des propriétés électriques de GaN en fonction de température.

Le prix Nobel de physique 2014 a été décerné pour l’invention de la diode électroluminescente (LED) bleue. La clé de la réussite de ce composant est la maitrise du dopage type p du GaN. Jusqu’à présent, le magnésium (Mg) reste la seule source de dopage de type p dans ce matériau. Or pour qu’il soit électriquement actif un procédé d’activation est nécessaire : soit par activation thermique, soit par irradiation avec des électrons.
Il est admis que l’activation du Mg passe par à une décomposition des complexes Mg-H. Pourtant, de nombreuses questions restent encore ouvertes concernant le mécanisme de dopage :
- rôle de l’hydrogène dans le mécanisme de croissance des matériaux de type p
- rôle de la direction de croissance sur le niveau de dopage
- rôle de l’oxygène dans le mécanisme d’activation.
Deux techniques de croissance de GaN dopé Mg sous haute pression d’azote conduisent à différents résultats :
- croissance spontanée (direction latérale) conduisant aux matériaux de type p activés dans les même conditions que les couches MOCVD
- croissance forcée (suivant l’axe C) conduisant aux matériaux fortement résistifs de type p ou type n.
Le modèle proposé d’états localisés de magnésium dans GaN stipule que l’activation du dopant conduit à l’apparition de trois niveaux distincts :
- un donneur peu profond (30 meV)
- un accepteur peu profond (150 meV)
- un accepteur profond (1 eV)

Un ensemble atomique en régime de blocage Rydberg dipolaire présente des non-linéarités optiques si fortes qu’elles deviennent potentiellement décelables sur des champs quantiques très faibles. Ces effets sont encore augmentés par la mise en cavité de l’échantillon atomique. Un tel milieu ouvre ainsi la voie à la réalisation d’interactions effectives déterministes entre photons, prérequis essentiel au traitement optique de l’information quantique. L’étude théorique de la dynamique d’un ensemble atomique en forte interaction est délicate, en tant qu’elle constitue un problème à N corps fortement corrélés. En utilisant différentes approches, phénoménologiques et perturbatives, qui seront brièvement décrites, nous analysons l’action de l’ensemble atomique sur la lumière quantique incidente – notamment sur la statistique quantique [1,2] et le spectre [3] du faisceau transmis. Ce travail théorique s’appuie sur les développements expérimentaux réalisés au sein de l’équipe Optique Quantique du laboratoire Charles Fabry de l’Institut d’Optique (Palaiseau).

[1] A Grankin et al., Quantum statistics of light transmitted through an intracavity Rydberg medium, New Journal of Physics 16, 043020 (2014).
[2] A. Grankin et al, Quantum-optical nonlinearities induced by Rydberg-Rydberg interactions: A perturbative approach, Phys. Rev. A 92, 043841 (2015).
[3] A Grankin et al, Inelastic photon scattering via the intracavity Rydberg blockade, Phys. Rev. Lett. 117, 253602 (2016).

There will be 2 talks in the topic:
1. Alexandre Douplik: Holographic Interferometry Imaging Monitoring of Photodynamic (PDT) Reactions in Biophantoms,
Exploration of photochemical and photothermal reaction due to interaction of light, molecular oxygen and human hemoglobin at presence of a photosensitizer has been carried out by Holographic Interferometry Imaging. PDT recently implied as a photochemical reaction involving light, photosensitive molecules absorbing light or photosensitizer (PS) and ambient molecular oxygen (O2) to generate reactive oxygen species (ROS) which in turn destroy biotissue as a surgical/therapeutic tool.
2. Aditya Pandya: 3D Tissue Mimicking Phantoms with Patterned Oxygenation States of Hemoglobin for Photoacoustic Applications:
Aluminium sulphonated phthalocyanine (AlPs) photosensitiser mixed with Hemoglobin (Hb) was used to create patterned oxygenation states of Hb in tissue mimicking gelatin phantoms. Spectrophotometric measurements of a temporal study of Hb conversion and an oxygenation patterned phantom monitored the photodynamic reaction.

Elementary excitations in dense media are renormalized by their mutual interaction, giving rise to quasiparticles with new collective properties. This renormalization has been observed in highly doped semiconductor quantum wells: Coulomb interaction ties together all the electronic excitations between confined states into a unique bright collective mode, a confined plasmon [1]. We have shown that confined plasmons have a superradiant nature: their spontaneous emission rate is proportional to the number of particles taking part in the collective excitation. This property has been experimentally demonstrated by performing emission spectra under electrical excitation, showing that spontaneous emission can be the dominant relaxation mechanism of plasmons [2].
In this talk I will discuss the possibility of exploiting the superradiant nature of confined plasmons to tailor the light-matter interaction in a doped quantum well [3] and realize novel quantum optoelectronic devices, such as directional and quasi-monochromatic incandescent sources [4]. I will also present devices based on spatially separated plasmons interacting through the electromagnetic field, resulting in Dicke superradiance and cooperative Lamb shift [5].

[1] A. Delteil et al., Phys. Rev. Lett. 109, 246808 (2012).
[2] T. Laurent et al., Phys. Rev. Lett. 115, 187402 (2015).
[3] S. Huppert et al., Phys. Rev. B 94, 155418 (2016).
[4] S. Huppert et al., ACS Photonics 2, 1663 (2015).
[6] G. Frucci et al., New Journal of Physics 19, 043006 (2017).

The readout of negatively charged nitrogen-vacancy (NV) centre electron spins is essential for applications in quantum computation, metrology and sensing. Conventional readout protocols are based on the detection of photons emitted from NV centres, a process limited by the efficiency of photon collection. Recently, we have introduced the photoelectrically detected magnetic resonance (PDMR) technique [1] that overcomes some of the drawbacks of optical methods [2]. We demonstrate pulsed photoelectric coherent manipulation and detection of NV centers [3] as a critical step towards using our technique for room temperature quantum computation devices. We develop novel pulse coherent operation schemes, specific for photocurrent, using high frequency laser and MW pulses encoded in low frequency envelope. Allowing thus to eliminate the photocurrent due to ionization of residual defects and downscale the detection from previous ~ 106 NVs to just 5 NVs centres. The pulsed envelope PDMR technique is demonstrated on Rabi and Ramsey sequences that are eminent tools for magnetometry and quantum protocols.

[1] E. Bourgeois, M. Gulka et al., Nature Comm. (2015)
[2] E. Bourgeois, M. Gulka et al., Phys. Rev. B (2017)
[3] M. Gulka et al., Phys. Rev. Applied (2017)

Imposing boundary conditions on the quantum vacuum can have interesting consequences. An example is the Casimir effect where fluctuations of the electromagnetic field lead to a force between metallic or dielectric objects. Accounting not only for quantum fluctuations but also for thermal fluctuations of the electromagnetic field, thermodynamic aspects of the Casimir effect can be studied. Interestingly, it was found that the entropy can become negative under appropriate circumstances. In particular, the dissipative nature of the objects involved as well as their geometrical shape are of relevance. We will explain the meaning of a negative Casimir entropy and its dissipative and
geometric origins.