147 research outputs found
Test of the isotopic and velocity selectivity of a lithium atom interferometer by magnetic dephasing
A magnetic field gradient applied to an atom interferometer induces a
-dependent phase shift which results in a series of decays and revivals of
the fringe visibility. Using our lithium atom interferometer based on Bragg
laser diffraction, we have measured the fringe visibility as a function of the
applied gradient. We have thus tested the isotopic selectivity of the
interferometer, the velocity selective character of Bragg diffraction for
different diffraction orders as well as the effect of optical pumping of the
incoming atoms. All these observations are qualitatively understood but a
quantitative analysis requires a complete model of the interferometer
Phase noise due to vibrations in Mach-Zehnder atom interferometers
Atom interferometers are very sensitive to accelerations and rotations. This
property, which has some very interesting applications, induces a deleterious
phase noise due to the seismic noise of the laboratory and this phase noise is
sufficiently large to reduce the fringe visibility in many experiments. We
develop a model calculation of this phase noise in the case of Mach-Zehnder
atom interferometers and we apply this model to our thermal lithium
interferometer. We are able to explain the observed phase noise which has been
detected through the rapid dependence of the fringe visibility with the
diffraction order. We think that the dynamical model developed in the present
paper should be very useful to reduce the vibration induced phase noise in atom
interferometers, making many new experiments feasible
Atom interferometry measurement of the electric polarizability of lithium
Using an atom interferometer, we have measured the static electric
polarizability of Li m atomic units with a 0.66% uncertainty. Our experiment, which
is similar to an experiment done on sodium in 1995 by D. Pritchard and
co-workers, consists in applying an electric field on one of the two
interfering beams and measuring the resulting phase-shift. With respect to D.
Pritchard's experiment, we have made several improvements which are described
in detail in this paper: the capacitor design is such that the electric field
can be calculated analytically; the phase sensitivity of our interferometer is
substantially better, near 16 mrad/; finally our interferometer is
species selective it so that impurities present in our atomic beam (other
alkali atoms or lithium dimers) do not perturb our measurement. The extreme
sensitivity of atom interferometry is well illustrated by our experiment: our
measurement amounts to measuring a slight increase of the atom
velocity when it enters the electric field region and our present
sensitivity is sufficient to detect a variation .Comment: 14 page
Parallel Temperatures in Supersonic Beams: Ultra Cooling of Light Atoms seeded in a Heavier Carrier Gas
We have found recently that, in a supersonic expansion of a mixture of two
monoatomic gases, the parallel temperatures of the two gases can be very
different. This effect is large if the seeded gas is highly diluted and if its
atomic mass is considerably smaller than the one of the carrier gas. In the
present paper, we present a complete derivation of our theoretical analysis of
this effect. Our calculation is a natural extension of the existing theory of
supersonic cooling to the case of a gas mixture, in the high dilution limit.
Finally, we describe a set of temperature measurements made on a beam of
lithium seeded in argon. Our experimental results are in very good agreement
with the results of our calculation.Comment: 24 novembre 200
Anomalous cooling of the parallel velocity in seeded beams
We have measured the parallel velocity distribution of a lithium supersonic
beam produced by seeding lithium in argon. The parallel temperature for lithium
is considerably lower than the calculated parallel temperature of the argon
carrier gas. We have extended the theory of supersonic cooling to calculate the
parallel temperature of the seeded gas, in the limit of high dilution. The
theoretical result thus obtained is in good agreement with ourobservations.Comment: 01 june 200
Statistics of counter-streaming solar wind suprathermal electrons at solar minimum : STEREO observations
Previous work has shown that solar wind suprathermal electrons can display a number of features in terms of their anisotropy. Of importance is the occurrence of counter-streaming electron patterns, i.e., with "beams" both parallel and anti-parallel to the local magnetic field, which is believed to shed light on the heliospheric magnetic field topology. In the present study, we use STEREO data to obtain the statistical properties of counter-streaming suprathermal electrons (CSEs) in the vicinity of corotating interaction regions (CIRs) during the period MarchâDecember 2007. Because this period corresponds to a minimum of solar activity, the results are unrelated to the sampling of large-scale coronal mass ejections, which can lead to CSE owing to their closed magnetic field topology. The present study statistically confirms that CSEs are primarily the result of suprathermal electron leakage from the compressed CIR into the upstream regions with the combined occurrence of halo depletion at 90° pitch angle. The occurrence rate of CSE is found to be about 15â20% on average during the period analyzed (depending on the criteria used), but superposed epoch analysis demonstrates that CSEs are preferentially observed both before and after the passage of the stream interface (with peak occurrence rate >35% in the trailing high speed stream), as well as both inside and outside CIRs. The results quantitatively show that CSEs are common in the solar wind during solar minimum, but yet they suggest that such distributions would be much more common if pitch angle scattering were absent. We further argue that (1) the formation of shocks contributes to the occurrence of enhanced counter-streaming sunward-directed fluxes, but does not appear to be a necessary condition, and (2) that the presence of small-scale transients with closed-field topologies likely also contributes to the occurrence of counter-streaming patterns, but only in the slow solar wind prior to CIRs
Lithium atom interferometer using laser diffraction : description and experiments
We have built and operated an atom interferometer of the Mach-Zehnder type.
The atomic wave is a supersonic beam of lithium seeded in argon and the mirrors
and beam-splitters for the atomic wave are based on elastic Bragg diffraction
on laser standing waves at 671 nm. We give here a detailed description of our
experimental setup and of the procedures used to align its components. We then
present experimental signals, exhibiting atomic interference effects with a
very high visibility, up to 84.5 %. We describe a series of experiments testing
the sensitivity of the fringe visibility to the main alignment defects and to
the magnetic field gradient.Comment: 8 avril 200
Statistics of counter-streaming solar wind suprathermal electrons at solar minimum: STEREO observations
Copyright © Author(s) 2010. This work is distributed
under the Creative Commons Attribution 3.0 LicenseOpen Access journalPrevious work has shown that solar wind suprathermal electrons can display a number of features in terms of their anisotropy. Of importance is the occurrence of counter-streaming electron patterns, i.e., with "beams" both parallel and anti-parallel to the local magnetic field, which is believed to shed light on the heliospheric magnetic field topology. In the present study, we use STEREO data to obtain the statistical properties of counter-streaming suprathermal electrons (CSEs) in the vicinity of corotating interaction regions (CIRs) during the period MarchâDecember 2007. Because this period corresponds to a minimum of solar activity, the results are unrelated to the sampling of large-scale coronal mass ejections, which can lead to CSE owing to their closed magnetic field topology. The present study statistically confirms that CSEs are primarily the result of suprathermal electron leakage from the compressed CIR into the upstream regions with the combined occurrence of halo depletion at 90° pitch angle. The occurrence rate of CSE is found to be about 15â20% on average during the period analyzed (depending on the criteria used), but superposed epoch analysis demonstrates that CSEs are preferentially observed both before and after the passage of the stream interface (with peak occurrence rate >35% in the trailing high speed stream), as well as both inside and outside CIRs. The results quantitatively show that CSEs are common in the solar wind during solar minimum, but yet they suggest that such distributions would be much more common if pitch angle scattering were absent. We further argue that (1) the formation of shocks contributes to the occurrence of enhanced counter-streaming sunward-directed fluxes, but does not appear to be a necessary condition, and (2) that the presence of small-scale transients with closed-field topologies likely also contributes to the occurrence of counter-streaming patterns, but only in the slow solar wind prior to CIRs
Studying Sun-Planet Connections Using the Heliophysics Integrated Observatory (HELIO)
The Heliophysics Integrated Observatory (HELIO) is a software infrastructure involving a collection of web services, heliospheric data sources (e.g., solar, planetary, etc.), and event catalogues â all of which are accessible through a unified front end. In this paper we use the HELIO infrastructure to perform three case studies based on solar events that propagate through the heliosphere. These include a coronal mass ejection that intersects both Earth and Mars, a solar energetic particle event that crosses the orbit of Earth, and a high-speed solar wind stream, produced by a coronal hole, that is observed in situ at Earth (L1). A ballistic propagation model is run as one of the HELIO services and used to model these events, predicting if they will interact with a spacecraft or planet and determining the associated time of arrival. The HELIO infrastructure streamlines the method used to perform these kinds of case study by centralising the process of searching for and visualising data, indicating interesting features on the solar disk, and finally connecting remotely observed solar features with those detected by in situ solar wind and energetic particle instruments. HELIO represents an important leap forward in European heliophysics infrastructure by bridging the boundaries of traditional scientific domains
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