915,981 research outputs found
Spontaneous emission rates of dipoles in photonic crystal membranes
We show theoretically that finite two-dimensional (2D) photonic crystals in
thin semiconductor membranes strongly modify the spontaneous emission rate of
embedded dipole emitters. Three-dimensional Finite-Difference Time-Domain
calculations show over 7 times inhibition and 15 times enhancement of the
emission rate compared to the vacuum emission rate for judiciously oriented and
positioned dipoles. The vertical index confinement in membranes strongly
enhances modifications of the emission rate as compared to vertically
unconfined 2D photonic crystals. The emission rate modifications inside the
membrane mimic the local electric field mode density in a simple 2D model. The
inhibition of emission saturates exponentially as the crystal size around the
source is increased, with a length that is inversely proportional to the
bandwidth of the emission gap. We obtain inhibition of emission only close to
the slab center. However, enhancement of emission persists even outside the
membrane, with a distance dependence which dependence can be understood by
analyzing the contributions to the spontaneous emission rate of the different
vertically guided modes of the membrane. Finally we show that the emission
changes can even be observed in experiments with ensembles of randomly oriented
dipoles, despite the contribution of dipoles for which no gap exists
Star Formation Rate from Dust Infrared Emission
We examine what types of galaxies the conversion formula from dust infrared
(IR) luminosity into the star formation rate (SFR) derived by
Kennicutt (1998) is applicable to. The ratio of the observed IR luminosity,
, to the intrinsic bolometric luminosity of the newly (\la 10
Myr) formed stars,
, of a galaxy can be determined by a mean dust opacity in the
interstellar medium and the activity of the current star formation. We find
that these parameters area being is very large, and many nearby normal and active star-forming
galaxies really fall in this area. It results from offsetting two effects of a
small dust opacity and a large cirrus contribution of normal galaxies relative
to starburst galaxies on the conversion of the stellar emission into the dust
IR emission. In conclusion, the SFR determined from the IR luminosity under the
assumption of like Kennicutt (1998) is reliable within
a factor of 2 for all galaxies except for dust rich but quiescent galaxies and
extremely dust poor galaxies.Comment: Accepted by ApJL: 6 pages (emulateapj5), 2 figures (one is an extra
figure not appeared in ApJL
Frequency-dependent spontaneous emission rate from CdSe and CdTe nanocrystals: influence of dark states
We studied the rate of spontaneous emission from colloidal CdSe and CdTe
nanocrystals at room temperature. The decay rate, obtained from luminescence
decay curves, increases with the emission frequency in a supra-linear way. This
dependence is explained by the thermal occupation of dark exciton states at
room temperature, giving rise to a strong attenuation of the rate of emission.
The supra-linear dependence is in agreement with the results of tight-binding
calculations.Comment: 11 page
Photo-emission rate of sQGP at finite density
We calculate the thermal spectral function of SYM plasma with finite density
using holographic technique. We take the RN-AdS black hole as the dual gravity
theory. In the presence of charge, vector modes of gravitational and
electromagnetic perturbation are coupled with each other. By introducing master
variables for these modes, we solve the coupled system and calculate spectral
function. We also calculated photoemission rate of SYM plasma from spectral
function for light like momentum, AC conductivity and their density dependence.
The suppression of the conductivity in high density is noticed, which might be
yet another mechanism for the Jet quenching phenomena in RHIC experiment.Comment: 27 pages, 10 figure
Graviton Emission in the Bulk from a Higher-Dimensional Schwarzschild Black Hole
We consider the evaporation of (4+n)-dimensional non-rotating black holes
into gravitons. We calculate the energy emission rate for gravitons in the bulk
obtaining analytical solutions of the master equation satisfied by all three
types (S,V,T) of gravitational perturbations. Our results, valid in the
low-energy regime, show a vector radiation dominance for every value of n,
while the relative magnitude of the energy emission rate of the subdominant
scalar and tensor radiation depends on n. The low-energy emission rate in the
bulk for gravitons is well below that for a scalar field, due to the absence of
the dominant l=0,1 modes from the gravitational spectrum. Higher partial waves
though may modify this behaviour at higher energies. The calculated low-energy
emission rate, for all types of degrees of freedom decreases with n, although
the full energy emission rate, integrated over all frequencies, is expected to
increase with n, as in the previously studied case of a bulk scalar field.Comment: 17 pages, 2 figures, minor corrections, accepted by Phys. Lett.
Photon Emission Rate Engineering using Graphene Nanodisc Cavities
In this work, we present a systematic study of the plasmon modes in a system
of vertically stacked pair of graphene discs. Quasistatic approximation is used
to model the eigenmodes of the system. Eigen-response theory is employed to
explain the spatial dependence of the coupling between the plasmon modes and a
quantum emitter. These results show a good match between the semi-analytical
calculation and full-wave simulations. Secondly, we have shown that it is
possible to engineer the decay rates of a quantum emitter placed inside and
near this cavity, using Fermi level tuning, via gate voltages and variation of
emitter location and polarization. We highlighted that by coupling to the
bright plasmon mode, the radiative efficiency of the emitter can be enhanced
compared to the single graphene disc case, whereas the dark plasmon mode
suppresses the radiative efficiency
Damped Bloch oscillations of cold atoms in optical lattices
The paper studies Bloch oscillations of cold neutral atoms in the optical
lattice. The effect of spontaneous emission on the dynamics of the system is
analyzed both analytically and numerically. The spontaneous emission is shown
to cause (i) the decay of Bloch oscillations with the decrement given by the
rate of spontaneous emission and (ii) the diffusive spreading of the atoms with
a diffusion coefficient depending on {\em both} the rate of spontaneous
emission and the Bloch frequency.Comment: 10 pages, 8 figure
Photon Emission from Ultrarelativistic Plasmas
The emission rate of photons from a hot, weakly coupled ultrarelativistic
plasma is analyzed. Leading-log results, reflecting the sensitivity of the
emission rate to scattering events with momentum transfers from to ,
have previously been obtained. But a complete leading-order treatment requires
including collinearly enhanced, inelastic processes such as bremsstrahlung.
These inelastic processes receive O(1) modifications from multiple scattering
during the photon emission process, which limits the coherence length of the
emitted radiation (the Landau-Pomeranchuk-Migdal effect). We perform a
diagrammatic analysis to identify, and sum, all leading-order contributions. We
find that the leading-order photon emission rate is not sensitive to
non-perturbative scale dynamics. We derive an integral equation for the
photon emission rate which is very similar to the result of Migdal in his
original discussion of the LPM effect. The accurate solution of this integral
equation for specific theories of interest will be reported in a companion
paper.Comment: 50 pages, 20 figures. Added references and minor rewordings:
published versio
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