94 research outputs found
Continuous Lyman-alpha generation by four-wave mixing in mercury for laser-cooling of antihydrogen
Cooling antihydrogen atoms is important for future experiments both to test
the fundamental CPT symmetry by high-resolution laser spectroscopy and also to
measure the gravitational acceleration of antimatter. Laser-cooling of
antihydrogen can be done on the strong 1S-2P transition at the wavelength of
Lyman-alpha (121.6nm). A continuous-wave laser at the Lyman-alpha wavelength
based on solid-state fundamental lasers is described. By using a two-photon and
a near one photon resonance a scan across the whole phasematching curve of the
four-wave mixing process is possible. Furthermore the influence of the beam
profile of one fundamental beam on the four-wave mixing process is studied.Comment: 4 pages, 4 figure
The influence of the Hall force on the vortex dynamics in type II superconductors
The effect of the Hall force on the pinning of vortices in type II
superconductors is considered. A field theoretic formulation of the pinning
problem allows a non-perturbative treatment of the influence of quenched
disorder. A self-consistent theory is constructed using the diagrammatic
functional method for the effective action, and an expression for the pinning
force for independent vortices as well as vortex lattices is obtained. We find
that the pinning force for a single vortex is suppressed by the Hall force at
low temperatures while it is increased at high temperatures. The effect of the
Hall force is more pronounced on a single vortex than on a vortex lattice. The
results of the self-consistent theory are shown to be in good agreement with
numerical simulations.Comment: 9 pages, 4 figures, published in Physical Review
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A semiconductor laser system for the production of antihydrogen
Laser-controlled charge exchange is a promising method for producing cold antihydrogen. Caesium atoms in Rydberg states collide with positrons and create positronium. These positronium atoms then interact with antiprotons, forming antihydrogen. Laser excitation of the caesium atoms is essential to increase the cross section of the charge-exchange collisions. This method was demonstrated in 2004 by the ATRAP collaboration by using an available copper vapour laser. For a second generation of charge-exchange experiments we have designed a new semiconductor laser system that features several improvements compared to the copper vapour laser. We describe this new laser system and show the results from the excitation of caesium atoms to Rydberg states within the strong magnetic fields in the ATRAP apparatus
Mode-locking in driven vortex lattices with transverse ac-drive and random pinning
We find mode-locking steps in simulated current-voltage characteristics of
driven vortex lattices with {\it random} pinning when an applied ac-current is
{\it perpendicular} to the dc-current. For low frequencies there is
mode-locking only above a non-zero threshold ac force amplitude, while for
large frequencies there is mode-locking for any small ac force. This is
consistent with the nature of {\it transverse} temporal order in the different
regimes in the absence of an applied ac-drive. For large frequencies the
magnitude of the fundamental mode-locked step depends linearly with the ac
force amplitude.Comment: 4 pages, 4 figures, .tar.gz fil
Trapped Antihydrogen in Its Ground State
Antihydrogen atoms are confined in an Ioffe trap for 15 to 1000 seconds --
long enough to ensure that they reach their ground state. Though
reproducibility challenges remain in making large numbers of cold antiprotons
and positrons interact, 5 +/- 1 simultaneously-confined ground state atoms are
produced and observed on average, substantially more than previously reported.
Increases in the number of simultaneously trapped antithydrogen atoms are
critical if laser-cooling of trapped antihydrogen is to be demonstrated, and
spectroscopic studies at interesting levels of precision are to be carried out
A semiconductor laser system for the production of antihydrogen
Laser-controlled charge exchange is a promising method for producing cold antihydrogen. Caesium atoms in Rydberg states collide with positrons and create positronium. These positronium atoms then interact with antiprotons, forming antihydrogen. Las er excitation of the caesium atoms is essential to increase the cross section of the charge-exchange collisions. This method was demonstrated in 2004 by the ATRAP collaboration by using an available copper vapour laser. For a second generation of charge-e xchange experiments we have designed a new semiconductor laser system that features several improvements compared to the copper vapour laser. We describe this new laser system and show the results from the excitation of caesium atoms to Rydberg states wit hin the strong magnetic fields in the ATRAP apparatus
Photoproduction of eta mesons from the neutron: cross sections and double polarization observable E
Photoproduction of mesons from neutrons} \abstract{Results from
measurements of the photoproduction of mesons from quasifree protons and
neutrons are summarized. The experiments were performed with the CBELSA/TAPS
detector at the electron accelerator ELSA in Bonn using the
decay. A liquid deuterium target was used for the
measurement of total cross sections and angular distributions. The results
confirm earlier measurements from Bonn and the MAMI facility in Mainz about the
existence of a narrow structure in the excitation function of . The current angular distributions show a forward-backward
asymmetry, which was previously not seen, but was predicted by model
calculations including an additional narrow state. Furthermore, data
obtained with a longitudinally polarized, deuterated butanol target and a
circularly polarized photon beam were analyzed to determine the double
polarization observable . Both data sets together were also used to extract
the helicity dependent cross sections and . The
narrow structure in the excitation function of
appears associated with the helicity-1/2 component of the reaction
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