12,195 research outputs found
Stimulated Raman Adiabatic Passage via bright state in Lambda medium of unequal oscillator strengths
We consider the population transfer process in a Lambda-type atomic medium of
unequal oscillator strengths by stimulated Raman adiabatic passage via
bright-state (b-STIRAP) taking into account propagation effects. Using both
analytic and numerical methods we show that the population transfer efficiency
is sensitive to the ratio q_p/q_s of the transition oscillator strengths. We
find that the case q_p>q_s is more detrimental for population transfer process
as compared to the case where . For this case it is possible to
increase medium dimensions while permitting efficient population transfer. A
criterion determining the interaction adiabaticity in the course of propagation
process is found. We also show that the mixing parameter characterizing the
population transfer propagates superluminally
Complete hyperfine Paschen-Back regime at relatively small magnetic fields realized in Potassium nano-cell
A one-dimensional nano-metric-thin cell (NC) filled with potassium metal has
been built and used to study optical atomic transitions in external magnetic
fields. These studies benefit from the remarkable features of the NC allowing
one to use - and -methods for effective investigations of
individual transitions of the K D_1 line. The methods are based on strong
narrowing of the absorption spectrum of the atomic column of thickness L equal
to and to (with \lambda = 770\un{nm} being the resonant
laser radiation wavelength). In particular, for a -polarized radiation
excitation the -method allows us to resolve eight atomic transitions
(in two groups of four atomic transitions) and to reveal two remarkable
transitions that we call Guiding Transitions (GT). The probabilities of all
other transitions inside the group (as well as the frequency slope versus
magnetic field) tend to the probability and to the slope of GT. Note that for
circular polarization there is one group of four transitions and GT do not
exist. Among eight transitions there are also two transitions (forbidden for
= 0) with the probabilities undergoing strong modification under the
influence of magnetic fields. Practically the complete hyperfine Paschen-Back
regime is observed at relatively low (\sim 1\un{kG}) magnetic fields. Note
that for K line GT are absent. Theoretical models describe the experiment
very well.Comment: 6 page
SIMULATING THE IMPACT OF INPUT-PRICE INFLATION ON FARM INCOME
Farm Management,
Scanning Tunneling Spectroscopy of Suspended Single-Wall Carbon Nanotubes
We have performed low-temperature STM measurements on single-wall carbon
nanotubes that are freely suspended over a trench. The nanotubes were grown by
CVD on a Pt substrate with predefined trenches etched into it. Atomic
resolution was obtained on the freestanding portions of the nanotubes.
Spatially resolved spectroscopy on the suspended portion of both metallic and
semiconducting nanotubes was also achieved, showing a Coulomb-staircase
behavior superimposed on the local density of states. The spacing of the
Coulomb blockade peaks changed with tip position reflecting a changing tip-tube
capacitance
Search for magnetic fields in particle-accelerating colliding-wind binaries
Some colliding-wind massive binaries, called particle-accelerating
colliding-wind binaries (PACWB), exhibit synchrotron radio emission, which is
assumed to be generated by a stellar magnetic field. However, no measurement of
magnetic fields in these stars has ever been performed. We aim at quantifying
the possible stellar magnetic fields present in PACWB to provide constraints
for models. We gathered 21 high-resolution spectropolarimetric observations of
9 PACWB available in the ESPaDOnS, Narval and HarpsPol archives. We analysed
these observations with the Least Squares Deconvolution method. We separated
the binary spectral components when possible. No magnetic signature is detected
in any of the 9 PACWB stars and all longitudinal field measurements are
compatible with 0 G. We derived the upper field strength of a possible field
that could have remained hidden in the noise of the data. While the data are
not very constraining for some stars, for several stars we could derive an
upper limit of the polar field strength of the order of 200 G. We can therefore
exclude the presence of strong or moderate stellar magnetic fields in PACWB,
typical of the ones present in magnetic massive stars. Weak magnetic fields
could however be present in these objects. These observational results provide
the first quantitative constraints for future models of PACWB.Comment: Accepted in A&
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