724 research outputs found
All-optical reconstruction of atomic ground-state population
The population distribution within the ground-state of an atomic ensemble is
of large significance in a variety of quantum optics processes. We present a
method to reconstruct the detailed population distribution from a set of
absorption measurements with various frequencies and polarizations, by
utilizing the differences between the dipole matrix elements of the probed
transitions. The technique is experimentally implemented on a thermal rubidium
vapor, demonstrating a population-based analysis in two optical pumping
examples. The results are used to verify and calibrate an elaborated numerical
model, and the limitations of the reconstruction scheme which result from the
symmetry properties of the dipole matrix elements are discussed.Comment: 6 pages, 4 figure
Storing images in warm atomic vapor
Reversible and coherent storage of light in atomic medium is a key-stone of
future quantum information applications. In this work, arbitrary
two-dimensional images are slowed and stored in warm atomic vapor for up to 30
s, utilizing electromagnetically induced transparency. Both the intensity
and the phase patterns of the optical field are maintained. The main limitation
on the storage resolution and duration is found to be the diffusion of atoms. A
techniqueanalogous to phase-shift lithography is employed to diminish the
effect of diffusion on the visibility of the reconstructed image
Measurement of Dicke Narrowing in Electromagnetically Induced Transparency
Dicke narrowing is a phenomena that dramatically reduces the Doppler width of
spectral lines, due to frequent velocity-changing collisions. A similar
phenomena occurs for electromagnetically induced transparency (EIT) resonances,
and facilitates ultra-narrow spectral features in room-temperature vapor. We
directly measure the Dicke-like narrowing by studying EIT line-shapes as a
function of the angle between the pump and the probe beams. The measurements
are in good agreement with an analytic theory with no fit parameters. The
results show that Dicke narrowing can increase substantially the tolerance of
hot-vapor EIT to angular deviations. We demonstrate the importance of this
effect for applications such as imaging and spatial solitons using a
single-shot imaging experiment, and discuss the implications on the feasibility
of storing images in atomic vapor.Comment: Introduction revise
Biogeomorphological response to river restoration of a suburban river with large wood: creating a restoration vision and cost-effectively monitoring the response trajectory using the citizen science MoRPh survey
Biogeomorphological responses to river restoration are rarely reported. Despite a transition in the emphasis and priorities of river management over the last 40 years from controlling river channel forms and processes to restoring and supporting natural processes, forms and functions, remarkably little information is available on project outcomes. Here, using the example of Beverley Brook within Wimbledon Common, Greater London, UK, we illustrate how standardised detailed monitoring information can be assembled at a very low cost using the citizen science MoRPh survey and we demonstrate the importance of having a pre-project vision of likely outcomes that can be tracked by the monitoring programme. We show how a pre-project and five post-project surveys undertaken over 4 years according to a before-after-control-impact (BACI) design provides scientifically robust data. Analysis of the survey data quantifies the nature, abundance and spatial distribution of restoration interventions, the immediate responses to those interventions, and the ensuing trajectory of biogeomorphological adjustments. Changes in the persistence, size, position, abundance and evolution of habitats reveal the degree to which the restoration achieved the pre-project biogeomorphological vision and why the recovery trajectory progressed at the observed rate and to the observed end point over 4 years. Our approach has enormous potential for monitoring the outcomes of river interventions. Whilst our project was limited in its spatial scale and focus on physical habitats, we suggest how these limitations could be overcome whilst still containing costs
Topological stability of stored optical vortices
We report an experiment in which an optical vortex is stored in a vapor of Rb
atoms. Due to its 2\pi phase twist, this mode, also known as the Laguerre-Gauss
mode, is topologically stable and cannot unwind even under conditions of strong
diffusion. To supplement our finding, we stored a flat phase Gaussian beam with
a dark center. Contrary to the optical vortex, which stays stable for over 100
microseconds, the dark center in the retrieved flat-phased image was filled
with light at storage times as small as 10 microseconds. This experiment proves
that higher electromagnetic modes can be converted into atomic coherences, and
that modes with phase singularities are robust to decoherence effects such as
diffusion. This opens the possibility to more elaborate schemes for two
dimensional information storage in atomic vapors.Comment: 4 pages, 4 figures v2: minor grammatical corrections v3: problem with
references fixed v4: minor clarifications added to the tex
The effects of the pre-pulse on capillary discharge extreme ultraviolet laser
In the past few years collisionally pumped extreme ultraviolet (XUV) lasers
utilizing a capillary discharge were demonstrated. An intense current pulse is
applied to a gas filled capillary, inducing magnetic collapse (Z-pinch) and
formation of a highly ionized plasma column. Usually, a small current pulse
(pre-pulse) is applied to the gas in order to pre-ionize it prior to the onset
of the main current pulse. In this paper we investigate the effects of the
pre-pulse on a capillary discharge Ne-like Ar XUV laser (46.9nm). The
importance of the pre-pulse in achieving suitable initial conditions of the gas
column and preventing instabilities during the collapse is demonstrated.
Furthermore, measurements of the amplified spontaneous emission (ASE)
properties (intensity, duration) in different pre-pulse currents revealed
unexpected sensitivity. Increasing the pre-pulse current by a factor of two
caused the ASE intensity to decrease by an order of magnitude - and to nearly
disappear. This effect is accompanied by a slight increase in the lasing
duration. We attribute this effect to axial flow in the gas during the
pre-pulse.Comment: 4 pages, 4 figure
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