106 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
Effects of thermal motion on electromagnetically induced absorption
We describe the effect of thermal motion and buffer-gas collisions on a
four-level closed N system interacting with strong pump(s) and a weak probe.
This is the simplest system that experiences electromagnetically induced
absorption (EIA) due to transfer of coherence via spontaneous emission from the
excited to ground state. We investigate the influence of Doppler broadening,
velocity-changing collisions (VCC), and phase-changing collisions (PCC) with a
buffer gas on the EIA spectrum of optically active atoms. In addition to exact
expressions, we present an approximate solution for the probe absorption
spectrum, which provides physical insight into the behavior of the EIA peak due
to VCC, PCC, and wave-vector difference between the pump and probe beams. VCC
are shown to produce a wide pedestal at the base of the EIA peak, which is
scarcely affected by the pump-probe angular deviation, whereas the sharp
central EIA peak becomes weaker and broader due to the residual Doppler-Dicke
effect. Using diffusion-like equations for the atomic coherences and
populations, we construct a spatial-frequency filter for a spatially structured
probe beam and show that Ramsey narrowing of the EIA peak is obtained for beams
of finite width
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
Theory of Dicke narrowing in coherent population trapping
The Doppler effect is one of the dominant broadening mechanisms in thermal
vapor spectroscopy. For two-photon transitions one would naively expect the
Doppler effect to cause a residual broadening, proportional to the wave-vector
difference. In coherent population trapping (CPT), which is a narrow-band
phenomenon, such broadening was not observed experimentally. This has been
commonly attributed to frequent velocity-changing collisions, known to narrow
Doppler-broadened one-photon absorption lines (Dicke narrowing). Here we show
theoretically that such a narrowing mechanism indeed exists for CPT resonances.
The narrowing factor is the ratio between the atom's mean free path and the
wavelength associated with the wave-vector difference of the two radiation
fields. A possible experiment to verify the theory is suggested.Comment: 6 pages, 2 figures; Introduction revise
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