Effets résonants et cohérents dans un cristal dopé aux ions erbium (oscillations cohérentes de population et transparence induite électromagnétiquement)

L'excitation optique résonante de systèmes atomiques permet de bénéficier d'une réponse non linéaire exacerbée, qui ouvre la voie au traitement de la lumière par la lumière, même à faible intensité lumineuse. Certaines interactions cohérentes de la lumière avec la matière permettent en outre de s'affranchir de la forte absorption associée à la résonance. Dans cette thèse, deux effets cohérents et résonants ont été explorés dans un cristal d'Y_2SiO_5 (YSO) dopé aux ions erbium 167 : les oscillations cohérentes de populations (OCP) et la transparence induite électromagnétiquement (TIE). Les OCP ont lieu dans un système atomique à deux niveaux d'énergie, excité par un faisceau d'intensité lentement variable. Dans cette thèse, les OCP ont notamment été utilisées pour ralentir la vitesse de propagation de la lumière dans le cristal à 3m/s. Nous avons également démontré le bénéfice que représente l'élargissement inhomogène pour ajuster le ralentissement et la transmission. La TIE est obtenue dans un système atomique à 3 niveaux d'énergie, dit en lambda, en excitant la cohérence Raman entre les 2 niveaux fondamentaux par 2 faisceaux optiques cohérents. Lors de la caractérisation de la structure hyperfine de l'erbium 167 dans le YSO par spectroscopie de résonance paramagnétique électronique et par spectroscopie de creusement spectral nous avons mis en évidence plusieurs systèmes en lambda, utilisables pour la TIE. Un dispositif expérimental basé sur la modulation d'amplitude d'un faisceau laser continu est utilisé pour générer les deux faisceaux cohérents et a permis d'observer la TIE pour la première fois à 1.5 m dans la matière condensée.Resonant optical excitation of atomic systems allows an enhanced non linear reponse where the control of light by light is possible even with low optical powers. Moreover some coherent light-matter interactions can reduce or annihilate the strong absorption associated with the resonant optical beam. In this thesis, two of these coherent and resonant interactions are studied using a Y_2SiO_5 (YSO) cristal lattice doped with erbium 167: coherent population oscillations (CPO) and electromagnetically induced transparency (EIT). CPO occurs in a two-level atomic system excited by an intensity modulated optical beam. In this work, CPO is used to demonstrate ultra-slow light propagation, down to 3m/s, in Er:YSO. Inhomogeneous broadening is specially used to tune both the slowing down and the transmission. EIT is obtained in a 3-level lambda-like atomic system, when excited on each transition by a coherent field. The hyperfine structure of erbium 167 ions in the YSO lattice is studied by electron spin resonance spectroscopy and optical hole-burning spectrocopy in order to identify several lambda-like systems. A dedicated experimental setup, where the intensity of a single laser beam is modulated in order to generate two coherent fields driving the lambda-like systems, is used for the demonstration of EIT at 1.5 m in an erbium-doped solid.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Where Brain, Body and World Collide

The production cross section of electrons from semileptonic decays of beauty hadrons was measured at mid-rapidity (|y| < 0.8) in the transverse momentum range 1 < pt < 8 Gev/c with the ALICE experiment at the CERN LHC in pp collisions at a center of mass energy sqrt{s} = 7 TeV using an integrated luminosity of 2.2 nb^{-1}. Electrons from beauty hadron decays were selected based on the displacement of the decay vertex from the collision vertex. A perturbative QCD calculation agrees with the measurement within uncertainties. The data were extrapolated to the full phase space to determine the total cross section for the production of beauty quark-antiquark pairs

MIRS: an imaging spectrometer for the MMX mission

International audienceThe MMX infrared spectrometer (MIRS) is an imaging spectrometer onboard MMX JAXA mission. MMX (Martian Moon eXploration) is scheduled to be launched in 2024 with sample return to Earth in 2029. MIRS is built at LESIA-Paris Observatory in collaboration with four other French laboratories, collaboration and financial support of CNES and close collaboration with JAXA and MELCO. The instrument is designed to fully accomplish MMX's scientific and measurement objectives. MIRS will remotely provide near-infrared spectral maps of Phobos and Deimos containing compositional diagnostic spectral features that will be used to analyze the surface composition and to support the sampling site selection. MIRS will also study Mars atmosphere, in particular spatial and temporal changes such as clouds, dust and water vapor

Higher harmonic anisotropic flow measurements of charged particles in Pb-Pb collisions at √sNN=2.76TeV

We report on the first measurement of the triangular nu(3), quadrangular nu(4), and pentagonal nu(5) charged particle flow in Pb-Pb collisions at root s(NN) = 2.76 TeV measured with the ALICE detector at the CERN Large Hadron Collider. We show that the triangular flow can be described in terms of the initial spatial anisotropy and its fluctuations, which provides strong constraints on its origin. In the most central events, where the elliptic flow nu(2) and nu(3) have similar magnitude, a double peaked structure in the two-particle azimuthal correlations is observed, which is often interpreted as a Mach cone response to fast partons. We show that this structure can be naturally explained from the measured anisotropic flow Fourier coefficients

Suppression of high transverse momentum D mesons in central Pb-Pb collisions at root s(NN)=2.76 TeV

The production of the prompt charm mesons D-0, D+, D*(+), and their antiparticles, was measured with the ALICE detector in Pb-Pb collisions at the LHC, at a centre-of-mass energy root s(NN) = 2.76 TeV per nucleon-nucleon collision. The p(t)-differential production yields in the range 2 < p(t) < 16 GeV/c at central rapidity, vertical bar y vertical bar < 0.5, were used to calculate the nuclear modification factor R-AA with respect to a proton-proton reference obtained from the cross section measured at root s = 7 TeV and scaled to root s = 2.76 TeV. For the three meson species, R-AA shows a suppression by a factor 3-4, for transverse momenta larger than 5 GeV/c in the 20% most central collisions. The suppression is reduced for peripheral collisions