464 research outputs found
Quantum lithography by coherent control of classical light pulses
The smallest spot in optical lithography and microscopy is generally limited
by diffraction. Quantum lithography, which utilizes interference between groups
of N entangled photons, was recently proposed to beat the diffraction limit by
a factor N. Here we propose a simple method to obtain N photons interference
with classical pulses that excite a narrow multiphoton transition, thus
shifting the "quantum weight" from the electromagnetic field to the
lithographic material. We show how a practical complete lithographic scheme can
be developed and demonstrate the underlying principles experimentally by
two-photon interference in atomic Rubidium, to obtain focal spots that beat the
diffraction limit by a factor of 2.Comment: 6 pages, 4 figures, Submitted to Opt. Expres
Theory of photospheric emission from relativistic outflows
In this paper we reexamine the optical depth of ultrarelativistic spherically
symmetric outflows and reevaluate the photospheric radius for each model during
both the acceleration and coasting phases. It is shown that for both the wind
and the shell models there are two asymptotic solutions for the optical depth
during the coasting phase of the outflow. In particular we show that quite
counterintuitively a geometrically thin shell may appear as a thick wind for
photons propagating inside it. For this reason we introduce notions of photon
thick and photon thin outflows, which appear more general and better physically
motivated with respect to winds and shells. Photosphere of relativistic outflow
is a dynamic surface. We study its geometry and find that the photosphere of
photon thin outflow has always a convex shape, while in the photon thick one it
is initially convex (there is always a photon thin layer in any outflow) and
then it becomes concave asymptotically approaching the photosphere of an
infinitely long wind. We find that both instantaneous and time integrated
observed spectra are very close to the thermal one for photon thick outflows,
in line with existing studies. It is our main finding that the photospheric
emission from the photon thin outflow produces non thermal time integrated
spectra, which may be described by the Band function well known in the GRB
literature. We find that energetic GRBs should produce photon thin outflows
with photospheric emission lasting less than one second for the total energy
erg and baryonic loading parameter . It means
that only time integrated spectra may be observed from such GRBs.Comment: Revision of the previous version, new effect is discussed.
Conclusions remain unchange
Constraining Sources of Ultra High Energy Cosmic Rays Using High Energy Observations with the Fermi Satellite
We analyze the conditions that enable acceleration of particles to ultra-high
energies, ~10^{20} eV (UHECRs). We show that broad band photon data recently
provided by WMAP, ISOCAM, Swift and Fermi satellites, yield constraints on the
ability of active galactic nuclei (AGN) to produce UHECRs. The high energy (MeV
- GeV) photons are produced by Compton scattering of the emitted low energy
photons and the cosmic microwave background or extra-galactic background light.
The ratio of the luminosities at high and low photon energies can therefore be
used as a probe of the physical conditions in the acceleration site. We find
that existing data excludes core regions of nearby radio-loud AGN as possible
acceleration sites of UHECR protons. However, we show that giant radio lobes
are not excluded. We apply our method to Cen A, and show that acceleration of
protons to ~10^{20} eV can only occur at distances >~ 100 kpc from the core.Comment: Extended discussion on former results; Accepted for publication in
JCA
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