9,101 research outputs found
Sub- and super-luminal light propagation using a Rydberg state
We present a theoretical study to investigate sub- and super-luminal light
propagation in a rubidium atomic system consisting of a Rydberg state by using
density matrix formalism. The analysis is performed in a 4-level vee+ladder
system interacting with a weak probe, and strong control and switching fields.
The dispersion and absorption profiles are shown for stationary atoms as well
as for moving atoms by carrying out Doppler averaging at room temperature. We
also present the group index variation with control Rabi frequency and observe
that a transparent medium can be switched from sub- to super-luminal
propagation in the presence of switching field. Finally, the transient response
of the medium is discussed, which shows that the considered 4-level scheme has
potential applications in absorptive optical switching.Comment: 12 pages, 6 figure
Study of a four-level system in vee + ladder configuration
We present the results of a theoretical study of a four-level atomic system
in vee + ladder configuration using a density matrix analysis. The absorption
and dispersion profiles are derived for a weak probe field and for varying
strengths of the two strong control fields. For specificity, we choose energy
levels of Rb, and present results for both stationary atoms and moving
atoms in room temperature vapor. An electromagnetically induced absorption
(EIA) peak with negative dispersion is observed at zero probe detuning when the
control fields have equal strengths, which switches to electromagnetically
induced transparency (EIT) with positive dispersion (due to splitting of the
EIA peak) when the control fields are unequal. There is significant linewidth
narrowing in thermal vapor.Comment: 6 pages, 4 figure
Can overturning motions in penumbral filaments be detected?
Numerical simulations indicate that the filamentation of sunspot penumbrae
and the associated systematic outflow (the Evershed effect) are due to
convectively driven fluid motions constrained by the inclined magnetic field.
We investigate whether these motions, in particular the upflows in the bright
filaments and the downflows at their edges can be reliably observed with
existing instrumentation. We use a snapshot from a sunspot simulation to
calculate 2D maps of synthetic line profiles for the spectral lines Fe\sci
7090.4 \AA ~ and C\sci 5380.34 \AA. The maps are spatially and spectrally
degraded according to typical instrument properties. Line-of-sight velocities
are determined from line bisector shifts. We find that the detectability of the
convective flows is strongly affected by spatial smearing, particularly so for
the downflows. Furthermore, the line-of-sight velocities are dominated by the
Evershed flow unless the observation is made very near to disk center. These
problems may have compromised recent attempts to detect overturning penumbral
convection. Lines with a low formation height are best suited to detect the
convective flows.Comment: 8 pages, 12 figures, accepted for publication in ApJ on 28th Ju
Carleson Measures and Logvinenko-Sereda sets on compact manifolds
Given a compact Riemannian manifold of dimension , we study the
space of functions of generated by eigenfunctions of eigenvalues less
than associated to the Laplace-Beltrami operator on . On these
spaces we give a characterization of the Carleson measures and the
Logvinenko-Sereda sets
Myrmica elmesi (Hymenoptera, Formicidae) a new species from Himalaya
Myrmica elmesi sp. n. is described from Himalaya. This species belongs to the pachei group of Myrmica speciesand is distinct from the species described in this group hitherto, which is represented by 14 species including three from Indian Himalaya. Myrmica elmesi is the fourth species of the diverse pachei group found in Himalaya; it was collected from the transitional zone and is described with notes on its ecology, this gains significance in the sense that ecology of most of the old world Myrmica is either unknown or poorly known
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