On the formation and decay of a molecular ultracold plasma

Double-resonant photoexcitation of nitric oxide in a molecular beam creates a dense ensemble of $50f(2)$ Rydberg states, which evolves to form a plasma of free electrons trapped in the potential well of an NO$^+$ spacecharge. The plasma travels at the velocity of the molecular beam, and, on passing through a grounded grid, yields an electron time-of-flight signal that gauges the plasma size and quantity of trapped electrons. This plasma expands at a rate that fits with an electron temperature as low as 5 K, colder that typically observed for atomic ultracold plasmas. The recombination of molecular NO$^+$ cations with electrons forms neutral molecules excited by more than twice the energy of the NO chemical bond, and the question arises whether neutral fragmentation plays a role in shaping the redistribution of energy and particle density that directs the short-time evolution from Rydberg gas to plasma. To explore this question, we adapt a coupled rate-equations model established for atomic ultracold plasmas to describe the energy-grained avalanche of electron-Rydberg and electron-ion collisions in our system. Adding channels of Rydberg predissociation and two-body, electron- cation dissociative recombination to the atomic formalism, we investigate the kinetics by which this relaxation distributes particle density and energy over Rydberg states, free electrons and neutral fragments. The results of this investigation suggest some mechanisms by which molecular fragmentation channels can affect the state of the plasma

Plasma Oscillations and Expansion of an Ultracold Neutral Plasma

We report the observation of plasma oscillations in an ultracold neutral plasma. With this collective mode we probe the electron density distribution and study the expansion of the plasma as a function of time. For classical plasma conditions, i.e. weak Coulomb coupling, the expansion is dominated by the pressure of the electron gas and is described by a hydrodynamic model. Discrepancies between the model and observations at low temperature and high density may be due to strong coupling of the electrons.Comment: 4 pages, 4 figures. Accepted Phys. Rev. Let

Search for weakly interacting sub-eV particles with the OSQAR laser-based experiment: results and perspectives

Recent theoretical and experimental studies highlight the possibility of new fundamental particle physics beyond the Standard Model that can be probed by sub-eV energy experiments. The OSQAR photon regeneration experiment looks for "Light Shining through a Wall" (LSW) from the quantum oscillation of optical photons into "Weakly Interacting Sub-eV Particles" (WISPs), like axion or axion-like particles (ALPs), in a 9 T transverse magnetic field over the unprecedented length of $2 \times 14.3$ m. No excess of events has been detected over the background. The di-photon couplings of possible new light scalar and pseudo-scalar particles can be constrained in the massless limit to be less than $8.0\times10^{-8}$ GeV$^{-1}$. These results are very close to the most stringent laboratory constraints obtained for the coupling of ALPs to two photons. Plans for further improving the sensitivity of the OSQAR experiment are presented.Comment: 7 pages, 7 figure

Latest Results of the OSQAR Photon Regeneration Experiment for Axion-Like Particle Search

The OSQAR photon regeneration experiment searches for pseudoscalar and scalar axion-like particles by the method of "Light Shining Through a Wall", based on the assumption that these weakly interacting sub-eV particles couple to two photons to give rise to quantum oscillations with optical photons in strong magnetic field. No excess of events has been observed, which constrains the di-photon coupling strength of both pseudoscalar and scalar particles down to $5.7 \cdot 10^{-8}$ GeV$^{-1}$ in the massless limit. This result is the most stringent constraint on the di-photon coupling strength ever achieved in laboratory experiments.Comment: 6 pages, 5 figures. appears in Proceedings of the 10th PATRAS Workshop on Axions, WIMPs and WISPs (2014

Effets non linéaires en optique guidée

Les non-linéarités sont largement présentes dans le monde qui nous entoure et font l'objet d'études de plus en plus approfondies. Malgré des non-linéarités très faibles, l'optique n'est pas en reste et a permis de mettre en évidence et d'exploiter des manifestations spectaculaires, mélanges de fréquences, effets paramétriques, etc. C'est l'avènement des lasers qui a permis la découverte des nonlinéarités optiques de volume, grâce à une augmentation des puissances optiques disponibles. Quant à elle, l'optique guidée a récemment permis d'ouvrir de nouveaux horizons à l'optique non linéaire, cette fois-ci en permettant de réaliser un rêve, celui de propager la lumière sur de grandes longueurs en s'affranchissant de la diffraction et de renforcer les effets non linéaires par accumulation. Toutefois ce domaine des effets non linéaires en optique guidée n'est sans doute encore qu'émergent, ainsi qu'en atteste la proportion élevée d'articles théoriques. De nombreuses réalisations expérimentales attractives demeurent irréalisables à cause d'exigences technologiques difficiles à atteindre. Le but du cours est de donner au lecteur un aperçu des résultats marquants des quinze dernières années et des tendances actuelles, en se limitant aux non-linéarités cubiques. Le choix a été fait d'aborder la plupart des aspects en privilégiant une description qualitative des phénomènes et une analyse intuitive des concepts, nécessairement incomplète, et de renvoyer le lecteur à des références pour plus de détails. La propagation en régime soliton, les non-linéarités dans les fibres, les dispositifs pour le traitement tout optique du signal, les effets spatiaux et dynamiques dans les coupleurs distribués, la spectroscopic des lignes noires figurent parmi les thèmes abordés