228,380 research outputs found
Effect of chromatic dispersion induced chirp on the temporal coherence property of individual beam from spontaneous four wave mixing
Temporal coherence of individual signal or idler beam, determined by the
spectral correlation property of photon pairs, is important for realizing
quantum interference among independent sources. To understand the effect of
chirp on the temporal coherence property, two series of experiments are
investigated by introducing different amount of chirp into either the pulsed
pump or individual signal (idler) beam. In the first one, based on spontaneous
four wave mixing in a piece of optical fiber, the intensity correlation
function of the filtered individual signal beam, which characterizes the degree
of temporal coherence, is measured as a function of the chirp of pump. The
results demonstrate that the chirp of pump pulses decreases the degree of
temporal coherence. In the second one, a Hong-Ou-Mandel type two-photon
interference experiment with the signal beams generated in two different fibers
is carried out. The results illustrate that the chirp of individual beam does
not change the temporal coherence degree, but affect the temporal mode
matching. To achieve high visibility, apart from improving the coherence degree
by minimizing the chirp of pump, mode matching should be optimized by managing
the chirps of individual beams.Comment: 17pages, 4figure
Quantum Treatment for Bose-Einstein Condensation in Non-Equilibrium Systems
We develop an approach based on stochastic quantum trajectories for an
incoherently pumped system of interacting bosons relaxing their energy in a
thermal reservoir. Our approach enables the study of the versatile coherence
properties of the system. We apply the model to exciton polaritons in a
semiconductor microcavity. Our results demonstrate the onset of macroscopic
occupation in the lowest-energy mode accompanied by the establishment of both
temporal and spatial coherence. We show that temporal coherence exhibits a
transition from a thermal to coherent statistics and the spatial coherence
reveals off-diagonal long-range order.Comment: 5 Pages, 3 figure
Temporal coherence length of light in semiclassical field theory models
The following work is motivated by the conceptual problems associated with
the wave-particle duality and the notion of the photon. Two simple classical
models for radiation from individual emitters are compared, one based on sines
with random phasejumps, another based on pulse trains. The sum signal is
calculated for a varying number of emitters. The focus lies on the final
signal's statistical features quantified by means of the temporal coherence
function and the temporal coherence length. We show how these features might be
used to experimentally differentiate between the models. We also point to
ambiguities in the definition of the temporal coherence length.Comment: 7 pages, 3 figures. The following article has been submitted to AIP
Conference Proceedings: Advances in Quantum Theory, Vaxjo 201
Loss of coherence in dynamical networks: spatial chaos and chimera states
We discuss the breakdown of spatial coherence in networks of coupled
oscillators with nonlocal interaction. By systematically analyzing the
dependence of the spatio-temporal dynamics on the range and strength of
coupling, we uncover a dynamical bifurcation scenario for the
coherence-incoherence transition which starts with the appearance of narrow
layers of incoherence occupying eventually the whole space. Our findings for
coupled chaotic and periodic maps as well as for time-continuous R\"ossler
systems reveal that intermediate, partially coherent states represent
characteristic spatio-temporal patterns at the transition from coherence to
incoherence.Comment: 4 pages, 4 figure
Coherence properties of the radiation from FLASH
FLASH is the first free electron laser user facility operating in the vacuum
ultraviolet and soft x-ray wavelength range. Many user experiments require
knowledge of the spatial and temporal coherence properties of the radiation. In
this paper we present an analysis of the coherence properties of the radiation
for the fundamental and for the higher odd frequency harmonics. We show that
temporal and spatial coherence reach maximum close to the FEL saturation but
may degrade significantly in the post-saturation regime. We also find that the
pointing stability of short FEL pulses is limited due to the fact that
non-azimuthal FEL eigenmodes are not sufficiently suppressed. We discuss
possible ways for improving the degree of transverse coherence and the pointing
stability.Comment: 17 pages, 19 figure
Semi-supervised Tuning from Temporal Coherence
Recent works demonstrated the usefulness of temporal coherence to regularize
supervised training or to learn invariant features with deep architectures. In
particular, enforcing smooth output changes while presenting temporally-closed
frames from video sequences, proved to be an effective strategy. In this paper
we prove the efficacy of temporal coherence for semi-supervised incremental
tuning. We show that a deep architecture, just mildly trained in a supervised
manner, can progressively improve its classification accuracy, if exposed to
video sequences of unlabeled data. The extent to which, in some cases, a
semi-supervised tuning allows to improve classification accuracy (approaching
the supervised one) is somewhat surprising. A number of control experiments
pointed out the fundamental role of temporal coherence.Comment: Under review as a conference paper at ICLR 201
Temporal Relations: Reference or Discourse Coherence?
The temporal relations that hold between events described by successive
utterances are often left implicit or underspecified. We address the role of
two phenomena with respect to the recovery of these relations: (1) the
referential properties of tense, and (2) the role of temporal constraints
imposed by coherence relations. We account for several facets of the
identification of temporal relations through an integration of these.Comment: To appear in the Proceedings of ACL-94, Student Session. 5 pages,
LaTeX source, requires lingmacros. Comments are welcom
- …