7,487 research outputs found
High-sensitivity imaging with multi-mode twin beams
Twin entangled beams produced by single-pass parametric down-conversion (PDC)
offer the opportunity to detect weak amount of absorption with an improved
sensitivity with respect to standard techniques which make use of classical
light sources. We propose a differential measurement scheme which exploits the
spatial quantum correlation of type II PDC to image a weak amplitude object
with a sensitivity beyond the standard quantum limit imposed by shot-noise.Comment: 13 pages, 8 figure
Quantum Mirrors and Crossing Symmetry as Heart of Ghost Imaging
In this paper it is proved that the key to understanding the ghost imaging
mystery are the crossing symmetric photon reactions in the nonlinear media.
Hence, the laws of the plane quantum mirror (QM) and that of spherical quantum
mirror, observed in the ghost imaging experiments, are obtained as natural
consequences of the energy-momentum conservation laws. So, it is shown that the
ghost imaging laws depend only on the energy-momentum conservation and not on
the photons entanglement. The extension of these results to the ghost imaging
with other kind of light is discussed. Some fundamental experiments for a
decisive tests of the [SPDC-DFG]-quantum mirror are suggested.Comment: 11 pages, 9 figure
Sintered silicon nitrode recuperator fabrication
The preliminary design and a demonstration of the feasibility of fabricating submodules of an automotive Stirling engine recuperator for waste heat recovery at 370 C are described. Sinterable silicon nitride (Sialon) tubing and plates were fabricated by extrusion and hydrostatic pressing, respectively, suitable for demonstrating a potential method of constructing ceramic recuperator-type heat exchangers. These components were fired in nitrogen atmosphere to 1800 C without significant scale formation so that they can be used in the as-fired condition. A refractory glass composition (Al2O3 x 4.5 CaO.MgO x 11SiO2) was used to join and seal component parts by a brazing technique which formed strong recuperator submodules capable of withstanding repeated thermal cycling to 1370 C. The corrosion resistance of these materials to Na2SO4 + NaCl carbon mixtures was also assessed in atmospheres of air, hydrogen and CO2-N2-H2O mixtures at both 870 C and 1370 C for times to 1000 hours. No significant reaction was observed under any of these test conditions
Coherent imaging of a pure phase object with classical incoherent light
By using the ghost imaging technique, we experimentally demonstrate the
reconstruction of the diffraction pattern of a {\em pure phase} object by using
the classical correlation of incoherent thermal light split on a beam splitter.
The results once again underline that entanglement is not a necessary feature
of ghost imaging. The light we use is spatially highly incoherent with respect
to the object (m speckle size) and is produced by a
pseudo-thermal source relying on the principle of near-field scattering. We
show that in these conditions no information on the phase object can be
retrieved by only measuring the light that passed through it, neither in a
direct measurement nor in a Hanbury Brown-Twiss (HBT) scheme. In general, we
show a remarkable complementarity between ghost imaging and the HBT scheme when
dealing with a phase object.Comment: 13 pages, 11 figures. Published in Physical Review A. Replaced
version fixes some problems with Figs. 1, 4 and 1
Detection of the ultranarrow temporal correlation of twin beams via sum-frequency generation
We demonstrate the ultranarrow temporal correlation (6 fs full width half
maximum) of twin beams generated by parametric down-conversion, by using the
inverse process of sum-frequency generation. The result relies on an achromatic
imaging of a huge bandwith of twin beams and on a careful control of their
spatial degrees of freedom. The detrimental effects of spatial filtering and of
imperfect imaging are shown toghether with the theoretical model used to
describe the results
Transforming nonlocality into frequency dependence: a shortcut to spectroscopy
Measurable spectra are theoretically very often derived from complicated
many-body Green's functions. In this way, one calculates much more information
than actually needed. Here we present an in principle exact approach to
construct effective potentials and kernels for the direct calculation of
electronic spectra. In particular, the potential that yields the spectral
function needed to describe photoemission turns out to be dynamical but {\it
local} and {\it real}. As example we illustrate this ``photoemission
potential'' for sodium and aluminium, modelled as homogeneous electron gas, and
discuss in particular its frequency dependence stemming from the nonlocality of
the corresponding self-energy. We also show that our approach leads to a very
short derivation of a kernel that is known to well describe absorption and
energy-loss spectra of a wide range of materials
Backscattering Differential Ghost Imaging in Turbid Media
In this Letter we present experimental results concerning the retrieval of
images of absorbing objects immersed in turbid media via differential ghost
imaging (DGI) in a backscattering configuration. The method has been applied,
for the first time to our knowledge, to the imaging of small thin black objects
located at different depths inside a turbid solution of polystyrene nanospheres
and its performances assessed via comparison with standard imaging techniques.
A simple theoretical model capable of describing the basic optics of DGI in
turbid media is proposed.Comment: 5 pages, 6 figure
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