2,815 research outputs found
Optical pattern formation with a 2-level nonlinearity
We present an experimental and theoretical investigation of spontaneous
pattern formation in the transverse section of a single retro-reflected laser
beam passing through a cloud of cold Rubidium atoms. In contrast to previously
investigated systems, the nonlinearity at work here is that of a 2-level atom,
which realizes the paradigmatic situation considered in many theoretical
studies of optical pattern formation. In particular, we are able to observe the
disappearance of the patterns at high intensity due to the intrinsic saturable
character of 2-level atomic transitions.Comment: 5 pages, 4 figure
Spatial correlations in hexagons generated via a Kerr nonlinearity
We consider the hexagonal pattern forming in the cross-section of an optical
beam produced by a Kerr cavity, and we study the quantum correlations
characterizing this structure. By using arguments related to the symmetry
broken by the pattern formation, we identify a complete scenario of six-mode
entanglement. Five independent phase quadratures combinations, connecting the
hexagonal modes, are shown to exhibit sub-shot-noise fluctuations. By means of
a non-linear quantum calculation technique, quantum correlations among the mode
photon numbers are demonstrated and calculated.Comment: ReVTeX file, 20 pages, 7 eps figure
Thick-medium model of transverse pattern formation in optically excited cold two-level atoms with a feedback mirror
We study a pattern-forming instability in a laser-driven optically thick cloud of cold two-level atoms with a planar feedback mirror. We develop a theoretical model, enabling a full analysis of transverse patterns in a medium with saturable nonlinearity, taking into account diffraction within the medium, and both the transmission and reflection gratings. The focus of the analysis is on the combined treatment of nonlinear propagation in a diffractively and optically thick medium and the boundary condition given by feedback. We demonstrate explicitly how diffraction within the medium breaks the degeneracy of Talbot modes inherent in thin-slice models. We predict the existence of envelope curves bounding all possible pattern-formation thresholds and illustrate their interaction with threshold curves by experimental observation of a sudden transition between length scales as mirror displacement is varied
Ingested foreign bodies and societal wealth: three year observational study of swallowed coins
Objective To examine the relation between coins ingested by children and the Dow Jones Industrial Average
Fluctuations and correlations in hexagonal optical patterns
We analyze the influence of noise in transverse hexagonal patterns in
nonlinear Kerr cavities. The near field fluctuations are determined by the
neutrally stable Goldstone modes associated to translational invariance and by
the weakly damped soft modes. However these modes do not contribute to the far
field intensity fluctuations which are dominated by damped perturbations with
the same wave vectors than the pattern. We find strong correlations between the
intensity fluctuations of any arbitrary pair of wave vectors of the pattern.
Correlation between pairs forming 120 degrees is larger than between pairs
forming 180 degrees, contrary to what a naive interpretation of emission in
terms of twin photons would suggest.Comment: 10 pages, 13 figure
Steps towards a map of the nearby universe
We present a new analysis of the Sloan Digital Sky Survey data aimed at
producing a detailed map of the nearby (z < 0.5) universe. Using neural
networks trained on the available spectroscopic base of knowledge we derived
distance estimates for about 30 million galaxies distributed over ca. 8,000 sq.
deg. We also used unsupervised clustering tools developed in the framework of
the VO-Tech project, to investigate the possibility to understand the nature of
each object present in the field and, in particular, to produce a list of
candidate AGNs and QSOs.Comment: 3 pages, 1 figure. To appear in Nucl Phys. B, in the proceedings of
the NOW-2006 (Neutrino Oscillation Workshop - 2006), R. Fogli et al. ed
All-optical delay line using semiconductor cavity solitons (vol 92, 011101, 2008)
Correction of Pedaci, F. and Barland, S. and Caboche, E. and Firth, W.J. and Oppo, G.L. and Tredicce, J.R. and Ackemann, T. and Scroggie, A.J. (2008) All-optical delay line using semiconductor cavity solitons. Applied Physics Letters, 92 (1). ISSN 0003-695
Frequency selection by soliton excitation in nondegenerate intracavity downconversion
We show that soliton excitation in intracavity downconversion naturally
selects a strictly defined frequency difference between the signal and idler
fields. In particular, this phenomenon implies that if the signal has smaller
losses than the idler then its frequency is pulled away from the cavity
resonance and the idler frequency is pulled towards the resonance and {\em vice
versa}. The frequency selection is shown to be closely linked with the relative
energy balance between the idler and signal fields.Comment: 5 pages, 3 figures. To appear in Phys Rev Let
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