On the suitability of longitudinal profile measurements using Coherent Smith-Purcell radiation for high current proton beams

The use of Smith-Purcell radiation to measure electrons longitudinal profiles has been demonstrated at several facilities in the picosecond and sub-picosecond range. There is a strong interest for the development of non intercepting longitudinal profile diagnostics for high current proton beams. We present here results of simulations on the expected yield of longitudinal profile monitors using Smith-Purcell radiation for such proton beams.Comment: Presented at IPAC 2014 - THPME08

Stimulated decay and formation of antihydrogen atoms

Antihydrogen atoms are routinely formed at the Antiproton Decelerator at CERN in a wide range of Rydberg states. To perform precision measurements, experiments rely on ground state antimatter atoms which are currently obtained only after spontaneous decay. In order to enhance the number of atoms in ground state, we propose and assess the efficiency of different methods to stimulate their decay. At first, we investigate the use of THz radiation to simultaneously couple all n-manifolds down to a low lying one with sufficiently fast spontaneous emission toward ground state. We further study a deexcitation scheme relying on state-mixing via microwave and/or THz light and a coupled (visible) deexcitation laser. We obtain close to unity ground state fractions within a few tens of microseconds for a population initiated in the n=30 manifold. Finally, we study how the production of antihydrogen atoms via stimulated radiative recombination can favourably change the initial distribution of states and improve the overall number of ground-state atoms when combined with the stimulated deexcitation proposed

Stimulated decay and formation of antihydrogen atoms

Antihydrogen atoms are routinely formed at the Antiproton Decelerator at CERN in a wide range of Rydberg states. To perform precision measurements, experiments rely on ground-state antimatter atoms which are currently obtained only after spontaneous decay. In order to enhance the number of atoms in ground state, we propose and assess the efficiency of different methods to stimulate their decay. First, we investigate the use of THz radiation to simultaneously couple all n-manifolds down to a low-lying one with sufficiently fast spontaneous emission toward ground state. We further study a deexcitation scheme relying on state mixing via microwave and/or THz light and a coupled (visible) deexcitation laser. We obtain close to unity ground-state fractions within a few tens of μs for a population initiated in the n=30 manifold. Finally, we study how the production of antihydrogen atoms via stimulated radiative recombination can favorably change the initial distribution of states and improve the overall number of ground-state atoms when combined with stimulated deexcitation.Antihydrogen atoms are routinely formed at the Antiproton Decelerator at CERN in a wide range of Rydberg states. To perform precision measurements, experiments rely on ground state antimatter atoms which are currently obtained only after spontaneous decay. In order to enhance the number of atoms in ground state, we propose and assess the efficiency of different methods to stimulate their decay. First, we investigate the use of THz radiation to simultaneously couple all n-manifolds down to a low lying one with sufficiently fast spontaneous emission toward ground state. We further study a deexcitation scheme relying on state-mixing via microwave and/or THz light and a coupled (visible) deexcitation laser. We obtain close to unity ground state fractions within a few tens of microseconds for a population initiated in the n=30 manifold. Finally, we study how the production of antihydrogen atoms via stimulated radiative recombination can favourably change the initial distribution of states and improve the overall number of ground-state atoms when combined with the stimulated deexcitation proposed

Engineering of spectral properties of two-photon states, preliminary results

We present an experimental implementation of spectral properties engineering on biphoton light, emitted via ultrafast type II spontaneous parametric down conversion (SPDC), based on the shaping of the pump pulse spectrum and propagation of the emitted correlated photons through dispersive media. Spectral properties ofa biphoton state are fully characterized by the two-photon spectral amplitude (TPSA). Exploiting the group velocity dispersion (GVD) induced by the passage of optical fields through dispersive media, an energy to time two dimensional Fourier transform of the TPSA is operated: this returns a technique to reconstruct TPSA by means of a temporal measurement among the delay between the laser pulse emission (trigger) and the detection times of the two correlated photons. Exploiting this kind of measurement it is possible to deeply resolve the interference pattern in the shape of TPSA. In this research we report on the conditions under which subtle structure on TPSA spectra can be deliberately engineered via modulation of the pump beam spectrum

Les représentations de la (des) science(s) dans l’enseignement : aspects épistémologiques, culturels et sociétaux

Ce numéro porte sur les représentations de la (des) science(s) véhiculées par différents acteurs éducatifs (auteurs de programmes ou de manuels, enseignants, élèves, etc.). Dans le texte introductif, Stéphanie Ruphy présente comment l’épistémologie contemporaine aborde la question de la délimitation/démarcation entre science et non-science. Les sept textes suivants visent à caractériser les représentations de la (des) science(s), à analyser les facteurs culturels et sociétaux qui peuvent les influencer et à en examiner les enjeux en particulier sur le plan éducatif. Ils ont en commun de chercher à dégager des résultats obtenus des pistes qui, non seulement, puissent contribuer à la recherche en didactique des sciences, mais aussi ouvrir plus largement à une réflexion sur le rôle de l’école et de l’enseignement des sciences dans des sociétés démocratiques et pluralistes confrontées à de nombreux défis, tant physiques et économiques (écologiques, climatiques) qu’idéologiques et sociaux (fondamentalismes religieux, crispations identitaires, etc.). Il s’agit aussi de s’interroger sur les conditions d’une culture scientifique émancipatrice. A la fin de ce numéro, deux « grands témoins » livrent leur réflexion sur celui-ci : Sébastien Charbonnier (philosophe) et Sarah Croché (sociologue). This issue focuses on the representations of the science(s)conveyed by different educational actors (authors of programs or textbooks, teachers, pupils, etc.). In the introductory text, Stéphanie Ruphy presents how contemporary epistemology addresses the question of delimitation / demarcation between science and not science. The following seven texts aim to characterize the representations of the science(s), to analyze the factors that can influence them, and to examine the stakes in particular in terms of education. They have in common to seek to derive tracks obtained from the results which, not only, can contribute to the research in science didactics, but also to open more widely to a reflection on the role of the school and the teaching of the science(s) in democratic and pluralistic societies facing many challenges, both physical and economic (ecological, climatic) and ideological and social (religious fundamentalisms, identity crispations, etc.). It is also to question of the conditions of an emancipatory scientific culture. At the end of this issue, two great witnesses give their thoughts on this one: Sébastien Charbonnier (philosopher) and Sarah Croché (sociologist)