608 research outputs found
Enhanced four-wave mixing via elimination of inhomogeneous broadening by coherent driving of quantum transition with control fields
We show that atoms from wide velocity interval can be concurrently involved
in Doppler-free two-photon resonant far from frequency degenerate four-wave
mixing with the aid of auxiliary electromagnetic field. This gives rise to
substantial enhancement of the output radiation generated in optically thick
medium. Numerical illustrations addressed to typical experimental conditions
are given.Comment: LaTeX2e, hyperref, 7 pages, 5 figures, to appear in PRA 1 august 200
Resonant nonlinear optics of backward waves in negative-index metamaterials
The extraordinary properties of resonant four-wave mixing of backward waves
in doped negative-index materials are investigated. The feasibility of
independent engineering of negative refractive index and nonlinear optical
response as well as quantum control of the nonlinear propagation process in
such composites is shown due to the coherent energy transfer from the control
to the signal field. Laser-induced transparency, quantum switching,
frequency-tunable narrow-band filtering, amplification, and realizing a
miniature mirrorless optical parametric generator of the entangled backward and
ordinary waves are among the possible applications of the investigated
processes.Comment: 10 pages, 9 figure
Nonlinear-optical Negative-index Metamaterials: Extraordinary Properties and Applications
The principles of nanoengineering of metamaterials which support optical electromagnetic and elastic
waves with negative group velocity are described. Extraordinary properties of nonlinear-optical energy
transfer between contra-propagating short pulses of electromagnetic and elastic waves are investigated
and prospective unique photonic devices are discussed.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3538
Negative-Index Metamaterials: Second-Harmonic Generation, Manley-Rowe Relations and Parametric Amplification
Second harmonic generation and optical parametric amplification in
negative-index metamaterials (NIMs) are studied. The opposite directions of the
wave vector and the Poynting vector in NIMs results in a "backward"
phase-matching condition, causing significant changes in the Manley-Rowe
relations and spatial distributions of the coupled field intensities. It is
shown that absorption in NIMs can be compensated by backward optical parametric
amplification. The possibility of distributed-feedback parametric oscillation
with no cavity has been demonstrated. The feasibility of the generation of
entangled pairs of left- and right-handed counter-propagating photons is
discussed.Comment: 7 pages, 6 figure
Structural and doping effects in the half-metallic double perovskite CrWO
he structural, transport, magnetic and optical properties of the double
perovskite CrWO with have been studied. By
varying the alkaline earth ion on the site, the influence of steric effects
on the Curie temperature and the saturation magnetization has been
determined. A maximum K was found for SrCrWO having an almost
undistorted perovskite structure with a tolerance factor . For
CaCrWO and BaCrWO structural changes result in a strong
reduction of . Our study strongly suggests that for the double perovskites
in general an optimum is achieved only for , that is, for an
undistorted perovskite structure. Electron doping in SrCrWO by a
partial substitution of Sr by La was found to reduce both
and the saturation magnetization . The reduction of could be
attributed both to band structure effects and the Cr/W antisites induced by
doping. Band structure calculations for SrCrWO predict an energy gap in
the spin-up band, but a finite density of states for the spin-down band. The
predictions of the band structure calculation are consistent with our optical
measurements. Our experimental results support the presence of a kinetic energy
driven mechanism in CrWO, where ferromagnetism is stabilized by a
hybridization of states of the nonmagnetic W-site positioned in between the
high spin Cr-sites.Comment: 14 pages, 10 figure
Quantum theory of resonantly enhanced four-wave mixing: mean-field and exact numerical solutions
We present a full quantum analysis of resonant forward four-wave mixing based
on electromagnetically induced transparency (EIT). In particular, we study the
regime of efficient nonlinear conversion with low-intensity fields that has
been predicted from a semiclassical analysis. We derive an effective nonlinear
interaction Hamiltonian in the adiabatic limit. In contrast to conventional
nonlinear optics this Hamiltonian does not have a power expansion in the fields
and the conversion length increases with the input power. We analyze the
stationary wave-mixing process in the forward scattering configuration using an
exact numerical analysis for up to input photons and compare the results
with a mean-field approach. Due to quantum effects, complete conversion from
the two pump fields into the signal and idler modes is achieved only
asymptotically for large coherent pump intensities or for pump fields in
few-photon Fock states. The signal and idler fields are perfectly quantum
correlated which has potential applications in quantum communication schemes.
We also discuss the implementation of a single-photon phase gate for continuous
quantum computation.Comment: 10 pages, 11 figure
Full quantum solutions to the resonant four-wave mixing of two single-photon wave packets
We analyze both analytically and numerically the resonant four-wave mixing of
two co-propagating single-photon wave packets. We present analytic expressions
for the two-photon wave function and show that soliton-type quantum solutions
exist which display a shape-preserving oscillatory exchange of excitations
between the modes. Potential applications including quantum information
processing are discussed.Comment: 7 pages, 3 figure
Magnetoelectric ordering of BiFeO3 from the perspective of crystal chemistry
In this paper we examine the role of crystal chemistry factors in creating
conditions for formation of magnetoelectric ordering in BiFeO3. It is generally
accepted that the main reason of the ferroelectric distortion in BiFeO3 is
concerned with a stereochemical activity of the Bi lone pair. However, the lone
pair is stereochemically active in the paraelectric orthorhombic beta-phase as
well. We demonstrate that a crucial role in emerging of phase transitions of
the metal-insulator, paraelectric-ferroelectric and magnetic disorder-order
types belongs to the change of the degree of the lone pair stereochemical
activity - its consecutive increase with the temperature decrease. Using the
structural data, we calculated the sign and strength of magnetic couplings in
BiFeO3 in the range from 945 C down to 25 C and found the couplings, which
undergo the antiferromagnetic-ferromagnetic transition with the temperature
decrease and give rise to the antiferromagnetic ordering and its delay in
regard to temperature, as compared to the ferroelectric ordering. We discuss
the reasons of emerging of the spatially modulated spin structure and its
suppression by doping with La3+.Comment: 18 pages, 5 figures, 3 table
Pion emission from the T2K replica target: method, results and application
The T2K long-baseline neutrino oscillation experiment in Japan needs precise
predictions of the initial neutrino flux. The highest precision can be reached
based on detailed measurements of hadron emission from the same target as used
by T2K exposed to a proton beam of the same kinetic energy of 30 GeV. The
corresponding data were recorded in 2007-2010 by the NA61/SHINE experiment at
the CERN SPS using a replica of the T2K graphite target. In this paper details
of the experiment, data taking, data analysis method and results from the 2007
pilot run are presented. Furthermore, the application of the NA61/SHINE
measurements to the predictions of the T2K initial neutrino flux is described
and discussed.Comment: updated version as published by NIM
Gluon polarization in the nucleon from quasi-real photoproduction of high-pT hadron pairs
We present a determination of the gluon polarization Delta G/G in the
nucleon, based on the helicity asymmetry of quasi-real photoproduction events,
Q^2<1(GeV/c)^2, with a pair of large transverse-momentum hadrons in the final
state. The data were obtained by the COMPASS experiment at CERN using a 160 GeV
polarized muon beam scattered on a polarized 6-LiD target. The helicity
asymmetry for the selected events is = 0.002 +- 0.019(stat.) +-
0.003(syst.). From this value, we obtain in a leading-order QCD analysis Delta
G/G=0.024 +- 0.089(stat.) +- 0.057(syst.) at x_g = 0.095 and mu^2 =~ 3
(GeV}/c)^2.Comment: 10 pages, 3 figure
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