124 research outputs found
New experimental limits on neutron - mirror neutron oscillations in the presence of mirror magnetic field
No full textInternational audiencePresent experimental and astrophysical limits do not exclude that the neutron (n) oscillation into mirror neutron ( ), a sterile state exactly degenerate in mass with the neutron, can be a very fast process, in fact faster than the neutron decay itself, in which case it would have very interesting implications in cosmology and astrophysics. This process is sensitive to the magnetic field. Namely, if the mirror magnetic field exists at the Earth, oscillation probability can be suppressed or resonantly amplified by the applied magnetic field , depending on its strength and on the angle between and . We present the results of ultra-cold neutron storage measurements aiming to check the anomalies observed in previous experiments which could be a signal for oscillation in the presence of mirror magnetic field G. From the analysis of the experimental data new lower limits on oscillation time as a function of were obtained, assuming that the mirror magnetic field is constant in time: s (95 % C.L.) for any between 0.08 and 0.17 G, and s (95 % C.L.) for any in the interval ( ) G
The mathematical modeling of the experiment on the determination of correlation coefficients in neutron beta-decay
No full textAttosecond control of electron localization in one- and two-color dissociative ionization of H2 and D2
No full textWe present one-color (IR) and two-color (single attosecond XUV pulse + IR) experiments where the sub-cycle evolution of the electric field of light is used to control the dissociative ionization of hydrogen and deuterium molecules
Attosecond control of electron localization in one- and two-color dissociative ionization of H2 and D2
No full textWe report experiments where an attosecond pulse launches a wavepacket on the dissociative state of D2 +, and a few-cycle IR pulse localizes the electron on one ionic fragment with attosecond sensitivity to the XUV-IR delay
Femtosecond time-resolved spectroscopy in polyatomic systems investigated by velocity-map imaging and high-order harmonic generation
No full textDans cette thèse, la dynamique de photodissociation de l'azoture de chlore (ClN3) est étudiée dans le domaine temporel par imagerie de vecteur vitesse des photofragments, spécialement du chlore et de N3. Cette imagerie résolue à l'échelle femtoseconde permet d'extraire les temps de dissociation, l'établissement temporel de la balance d'énergie de la réaction ainsi que la conservation des moments. Cette étude a permis de différencier deux domaines d'énergie: l'un menant à la formation d'un fragment N3 linéaire (étude autour de 4.5 eV d'excitation électronique) et le plus intéressant aboutissant à la formation d'un fragment N3 cyclique (autour de 6 eV).
Dans une seconde étude, la dynamique de relaxation électronique du tétrathiafulvalène (C6H4S4-TTF) est étudiée autour de 4 eV par spectroscopie de masse résolue en temps ainsi que par spectroscopie de photoélectron. Les seuils d'ionisation dissociative sont extraits d'une détection en coïncidence entre les photoélectrons de seuil et les fragments ionisés réalisée sur rayonnement synchrotron.
Les deux dernières expériences sont basées sur la génération d'harmoniques d'ordre élevé dans l'XUV d'une impulsion femtoseconde à 800 nm ou à 400 nm. Dans la première expérience, les harmoniques sont couplées à un imageur de vecteur vitesse en tant que rayonnement secondaire VUV. Par imagerie de photoélectron résolue en temps, nous avons révélé ainsi les dynamiques de relaxation des états de Rydberg initiée par une impulsion femtoseconde XUV à 15.5 eV dans l'argon et à 9.3 eV dans l'acétylène. Dans la seconde expérience, couramment nommée spectroscopie attoseconde, les harmoniques constituent le signal pompe sonde. Deux types de spectroscopie attoseconde ont été réalisés pour étudier la dynamique vibrationnelle de SF6: une expérience en réseau transitoire créé par deux impulsions pompe Raman avec une impulsion sonde intense générant les harmoniques à partir du réseau d'excitation et une expérience d'interférence de deux rayonnement XUV en champ lointain créés par deux impulsions sonde intensesRevealing the underlying ultrafast dynamics in molecular reaction spectroscopy demands state-of-the-art imaging techniques to follow a molecular process step by step.
Femtosecond time-resolved velocity-map imaging is used to study the photodissociation dynamics of chlorine azide (ClN3). Here especially the co-fragments chlorine and N3 are studied on the femtosecond timescale in two excitation energy regions around 4.67 eV and 6.12 eV, leading to the formation of a linear N3 fragment and a cyclic N3 fragment, respectively. This work is the first femtosecond spectroscopy study revealing the formation of cyclic N3. Tetrathiafulvalene (TTF, C6H4S4) electronic relaxation is studied, while scanning the electronic excitation around 4 eV, by time resolved mass and photoelectron spectroscopy. As only few is known about the ion continuum about TTF the imaging photoelectron photoion coincidence (iPEPICO) technique is used in order to disentangle the complex ionic dissociation. The second part of the thesis is based on the generation and application of XUV light pulses by high-order harmonic generation with an intense femtosecond laser pulse in a molecular target. Two types of phase sensitive attosecond spectroscopy experiments were conducted to study the vibrational dynamics of SF6: one using strong field transient grating spectroscopy, where high-order harmonic generation takes place in a grating of excitation, and the second experiment using high-order harmonic interferometry using two intense XUV probe pulses. The temporal dependencies in phase and amplitude reveal the vibrational dynamics in SF6 and demonstrate that high-order harmonic generation is sensitive to the internal excitations. Last but not least, the use of high-order harmonics as a XUV photon source for the velocity-map imaging spectrometer is investigated. Using time-resolved photoelectron imaging, the relaxation dynamics initiated with 15.5 eV in argon and 9.3 eV in acetylene are reveale
Comment on the Paper: "Synthesis and Electrochemical Study of Antifluorite-type Phases in the Li-M-N-O (M = Ti, V) Systems"
No full textMolecular Dissociative Ionization and Wave-Packet Dynamics Studied Using Two-Color XUV and IR Pump-Probe Spectroscopy
No full textWe present a combined theoretical and experimental study of ultrafast wave-packet dynamics in the
dissociative ionization of H2 molecules as a result of irradiation with an extreme-ultraviolet (XUV) pulse
followed by an infrared (IR) pulse. In experiments where the duration of both the XUVand IR pulses are
shorter than the vibrational period of H2+, dephasing and rephasing of the vibrational wave packet that is
formed in H2+ upon ionization of the neutral molecule by the XUV pulse is observed. In experiments
where the duration of the IR pulse exceeds the vibrational period of H2+ (15 fs), a pronounced dependence
of the Hþ kinetic energy distribution on XUV-IR delay is observed that can be explained in terms of the
adiabatic propagation of the H2+ wave packet on field-dressed potential energy curves
Probing the high latitude ionosphere from ground-based observations: The state of current knowledge and capabilities during IPY (2007-2009)
No full textDuring the International Polar Year (IPY), one area of great interest is co-coordinated, multi-instrument probing of the ionosphere at high latitudes. This region is important not only for the applications that rely upon our understanding of it, but also because it contains the footprints of processes that have their origin in the interplanetary space. Many different techniques are now available for probing the ionosphere, from radar measurements to the analysis of very low frequency (VLF) wave paths. Combining these methods provides the ability to study the ionosphere from high in the F-region to the bottom of the D-layer. Thus, coupling processes from the magnetosphere and to the neutral atmosphere can be considered. An additional dimension is through comparisons of the response of the two polar ionospheres to similar (or the same) geomagnetic activity. With more instruments available at the South Pole inter-hemispheric, studies have become easier to accomplish such that a fuller picture of the global response to Sun-Earth coupling can be painted. This paper presents a review of the current state of knowledge in ionospheric probing. It cannot provide a comprehensive guide of the work to date due to the scale of the topic. Rather it is intended to give an overview of the techniques and recent results from some of the instruments and facilities that are a part of the IPY cluster 63-Heliosphere Impact on Geospace. In this way it is hoped that the reader will gain a flavor of the recent research performed in this area and the potential for continuing collaboration and capabilities during the IP
Investigation of Ba-Fe-O System near the BaFe<sub>12</sub>O<sub>19</sub>
No full textThis article presents an investigation on phase equilibria of barium hexaferrite and neighboring phases near its melting point and on the characteristics of the compounds in the vicinity of BaFe12O19 phase. Fe3O4, BaFe22+Fe163+O27 (W type), BaFe2+Fe143+O23 (X type), BaFe12O19 (M type), Ba2Fe22+Fe123+O22 (Y type), Ba3Fe22+Fe243+O41 (Z type) and BaFe2O4 (S type) were detected in the molten and solidified stoichiometric BaFe12O19. Literature data are summarized and compared with results of the present work.</jats:p
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