2,028 research outputs found
Cold atom confinement in an all-optical dark ring trap
We demonstrate confinement of Rb atoms in a dark, toroidal optical
trap. We use a spatial light modulator to convert a single blue-detuned
Gaussian laser beam to a superposition of Laguerre-Gaussian modes that forms a
ring-shaped intensity null bounded harmonically in all directions. We measure a
1/e spin-relaxation lifetime of ~1.5 seconds for a trap detuning of 4.0 nm. For
smaller detunings, a time-dependent relaxation rate is observed. We use these
relaxation rate measurements and imaging diagnostics to optimize trap alignment
in a programmable manner with the modulator. The results are compared with
numerical simulations.Comment: 5 pages, 4 figure
Analysis of Residue Probability Density Function and Comparator Offset Error in Pipelined ADCs
This paper presents a new approach to analyze the convergence of residue probability density function (pdf) in pipelined ADCs. Compared to the previous approaches, in the proposed approach, in addition to the analysis of residue pdfs for different input densities, the analysis of the sub-ADC comparator offsets impact on output pdf is possible. Using Fourier analysis, it will be shown that the residue density converges to uniformity. In the half-bit redundant structure, residue pdf concentrates in the center half of the stage full-scale range and 6 dB of extra resolution can be gained. Also, the share of each stage in this resolution improvement is investigated. Examining the sub-ADC threshold offsets impact on residue pdfs, it is observed that with respect to the impact on converter additional resolution, the final stages offset errors are more significant than the first stages offsets
A low-loss photonic silica nanofiber for higher-order modes
Optical nanofibers confine light to subwavelength scales, and are of interest
for the design, integration, and interconnection of nanophotonic devices. Here
we demonstrate high transmission (> 97%) of the first family of excited modes
through a 350 nm radius fiber, by appropriate choice of the fiber and precise
control of the taper geometry. We can design the nanofibers so that these modes
propagate with most of their energy outside the waist region. We also present
an optical setup for selectively launching these modes with less than 1%
fundamental mode contamination. Our experimental results are in good agreement
with simulations of the propagation. Multimode optical nanofibers expand the
photonic toolbox, and may aid in the realization of a fully integrated
nanoscale device for communication science, laser science or other sensing
applications.Comment: 12 pages, 5 figures, movies available onlin
Magnetically-controlled velocity selection in a cold atom sample using stimulated Raman transitions
We observe velocity-selective two-photon resonances in a cold atom cloud in
the presence of a magnetic field. We use these resonances to demonstrate a
simple magnetometer with sub-mG resolution. The technique is particularly
useful for zeroing the magnetic field and does not require any additional laser
frequencies than are already used for standard magneto-optical traps. We verify
the effects using Faraday rotation spectroscopy.Comment: 5 pages, 6 figure
Photoassociation of sodium in a Bose-Einstein condensate
We report on the formation of ultra-cold Na molecules using single-photon
photoassociation of a Bose-Einstein condensate. The photoassociation rate,
linewidth and light shift of the J=1, vibrational level of the
\mterm{A}{1}{+}{u} molecular bound state have been measured. We find that the
photoassociation rate constant increases linearly with intensity, even where it
is predicted that many-body effects might limit the rate. Our observations are
everywhere in good agreement with a two-body theory having no free parameters.Comment: Fixes to the figures and references. Just the normal human stupidity
type stuff, nothing Earth-shatterin
Experimental determination of the evolution of the Bjorken integral at low Q^2
We extract the Bjorken integral Gamma^{p-n}_1 in the range 0.17 < Q^2 < 1.10
GeV^2 from inclusive scattering of polarized electrons by polarized protons,
deuterons and 3He, for the region in which the integral is dominated by nucleon
resonances. These data bridge the domains of the hadronic and partonic
descriptions of the nucleon. In combination with earlier measurements at higher
Q^2, we extract the non-singlet twist-4 matrix element f_2.Comment: Quoted world data updated. Minor change in some results, Minor
rephrasin
The Jlab Upgrade - Studies of the Nucleon with CLAS12
An overview is presented on the program to study the nucleon structure at the
12 GeV JLab upgrade using the CLAS12 detector. The focus is on deeply virtual
exclusive processes to access the generalized parton distributions,
semni-inclusive processes to study transverse momentum dependent distribution
functions, and inclusive spin structure functions and resonance transition form
factors at high Q^2 and with high precision.Comment: 7 pages, 12 figures, NSTAR 2007 conference, Bonn, September 5-8, 200
The Charge Form Factor of the Neutron at Low Momentum Transfer from the Reaction
We report new measurements of the neutron charge form factor at low momentum
transfer using quasielastic electrodisintegration of the deuteron.
Longitudinally polarized electrons at an energy of 850 MeV were scattered from
an isotopically pure, highly polarized deuterium gas target. The scattered
electrons and coincident neutrons were measured by the Bates Large Acceptance
Spectrometer Toroid (BLAST) detector. The neutron form factor ratio
was extracted from the beam-target vector asymmetry
at four-momentum transfers , 0.20, 0.29 and 0.42
(GeV/c).Comment: 5 pages, 3 figures, submitted to Phys. Rev. Let
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