10,132 research outputs found
Incoherent Mollow triplet
A counterpart of the Mollow triplet (luminescence lineshape of a two-level
system under coherent excitation) is obtained for the case of incoherent
excitation in a cavity. Its analytical expression, in excellent agreement with
numerical results, pinpoints analogies and differences between the conventional
resonance fluorescence spectrum and its cavity QED analogue under incoherent
excitation.Comment: 4 pages, 3 figure
Non-thermal processes in bowshocks of runaway stars. Application to Zeta Oph
Runaway massive stars are O- and B-type stars with high spatial velocities
with respect to the interstellar medium. These stars can produce bowshocks in
the surrounding gas. Bowshocks develop as arc-shaped structures, with bows
pointing to the same direction as the stellar velocity, while the star moves
supersonically through the interstellar gas. The piled-up shocked matter emits
thermal radiation and a population of locally accelerated relativistic
particles is expected to produce non-thermal emission over a wide range of
energies. We aim to model the non-thermal radiation produced in these sources.
Under some assumptions, we computed the non-thermal emission produced by the
relativistic particles and the thermal radiation caused by free-free
interactions, for O4I and O9I stars. We applied our model to Zeta Oph (HD
149757), an intensively studied massive star seen from the northern hemisphere.
This star has spectral type O9.5V and is a well-known runaway. Spectral energy
distributions of massive runaways are predicted for the whole electromagnetic
spectrum. We conclude that the non-thermal radiation might be detectable at
various energy bands for relatively nearby runaway stars, especially at
high-energy gamma rays. Inverse Compton scattering with photons from the heated
dust gives the most important contribution to the high-energy spectrum. This
emission approaches Fermi sensitivities in the case of Zeta Oph.Comment: 11 pages, 11 figures.- Accepted for publication in A&A
Runaway massive stars as variable gamma-ray sources
Runaway stars are ejected from their formation sites well within molecular
cores in giant dark clouds. Eventually, these stars can travel through the
molecular clouds, which are highly inhomogeneous. The powerful winds of massive
runaway stars interact with the medium forming bowshocks. Recent observations
and theoretical modelling suggest that these bowshocks emit non-thermal
radiation. As the massive stars move through the inhomogeneous ambient gas the
physical properties of the bowshocks are modified, producing changes in the
non-thermal emission. We aim to compute the non-thermal radiation produced in
the bowshocks of runaway massive stars when travelling through a molecular
cloud. We calculate the non-thermal emission and absorption for two types of
massive runaway stars, an O9I and an O4I, as they move through a density
gradient. We present the spectral energy distributions for the runaway stars
modelled. Additionally, we obtain light curves at different energy ranges. We
find significant variations in the emission over timescales of 1 yr. We
conclude that bowshocks of massive runaway stars, under some assumptions, might
be variable gamma-ray sources, with variability timescales that depend on the
medium density profile. These objects might constitute a population of galactic
gamma-ray sources turning on and off within years.Comment: 10 pages, 13 figures, accepted for publication in Astronomy &
Astrophysic
Quantitative Description of Strong-Coupling of Quantum Dots in Microcavities
We have recently developed a self-consistent theory of Strong-Coupling in the
presence of an incoherent pumping [arXiv:0807.3194] and shown how it could
reproduce quantitatively the experimental data [PRL 101, 083601 (2008)]. Here,
we summarize our main results, provide the detailed analysis of the fitting of
the experiment and discuss how the field should now evolve beyond merely
qualitative expectations, that could well be erroneous even when they seem to
be firmly established.Comment: Submitted to the AIP Conference Proceedings Series for the ICPS 2008
(Rio de Janeiro). 2 pages, reduced-quality figur
Computation of the equilibrium composition of reacting gas-solid mixtures with material and energy balance constraints Status report
Equilibrium composition computed for reacting- gas-solid composite materials using material and energy constraint
The Effects of Inlet Flow Modification on Cavitating Inducer Performance
This paper explores the effect of inlet flow modification on the cavitating and noncavitating performance of two cavitating inducers, one of simple helical design and the other a model of the low-pressure LOX pump in the Space Shuttle Main Engine. The modifications were generated by sections of honeycomb, both uniform and nonuniform. Significant improvement in the performance over a wide range of flow coefficients resulted from the use of either honeycomb section. Measurements of the axial and swirl velocity profiles of the flows entering the inducers were made in order to try to understand the nature of the inlet flow and the manner in which it is modified by the honeycomb sections
Lasing in Strong Coupling
An almost ideal thresholdless laser can be realized in the strong-coupling
regime of light-matter interaction, with Poissonian fluctuations of the field
at all pumping powers and all intensities of the field. This ideal scenario is
thwarted by quantum nonlinearities when crossing from the linear to the
stimulated emission regime, resulting in a universal jump in the second order
coherence, which measurement could however be used to establish a standard of
lasing in strong coupling.Comment: 5 pages, 2 figure
Optimization of photon correlations by frequency filtering
Photon correlations are a cornerstone of Quantum Optics. Recent works [NJP 15
025019, 033036 (2013), PRA 90 052111 (2014)] have shown that by keeping track
of the frequency of the photons, rich landscapes of correlations are revealed.
Stronger correlations are usually found where the system emission is weak.
Here, we characterize both the strength and signal of such correlations,
through the introduction of the 'frequency resolved Mandel parameter'. We study
a plethora of nonlinear quantum systems, showing how one can substantially
optimize correlations by combining parameters such as pumping, filtering
windows and time delay.Comment: Small updates to take into account the recent experimental
observation of the physics here analyze
Effective cavity pumping from weakly coupled quantum dots
We derive the effective cavity pumping and decay rates for the master
equation of a quantum dot-microcavity system in presence of weakly coupled
dots. We show that the in-flow of photons is not linked to the out-flow by
thermal equilibrium relationships.Comment: 6 pages, 1 figure, PLMCN10 conference proceeding
A mechanism for fast radio bursts
Fast radio bursts are mysterious transient sources likely located at
cosmological distances. The derived brightness temperatures exceed by many
orders of magnitude the self-absorption limit of incoherent synchrotron
radiation, implying the operation of a coherent emission process. We propose a
radiation mechanism for fast radio bursts where the emission arises from
collisionless Bremsstrahlung in strong plasma turbulence excited by
relativistic electron beams. We discuss possible astrophysical scenarios in
which this process might operate. The emitting region is a turbulent plasma hit
by a relativistic jet, where Langmuir plasma waves produce a concentration of
intense electrostatic soliton-like regions (cavitons). The resulting radiation
is coherent and, under some physical conditions, can be polarised and have a
power-law distribution in energy. We obtain radio luminosities in agreement
with the inferred values for fast radio bursts. The timescale of the radio
flare in some cases can be extremely fast, of the order of s. The
mechanism we present here can explain the main features of fast radio bursts
and is plausible in different astrophysical sources, such as gamma-ray bursts
and some Active Galactic Nuclei.Comment: 6 pages, 1 figure. Accepted for publication in Phys. Rev.
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